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Artist's conception of GPS Block II-F satellite in orbit
Civilian GPS receiver ("GPS navigation device") in a marine application.
GPS receivers are now integrated in many mobile phones.
.The Global Positioning System (GPS) is a U.S. space-based global navigation satellite system.^ GALILEO - European satellite navigation system.

^ The goal was development of a space-based, highly accurate navigation system.
  • Contributions of the Global Positioning System 27 January 2010 23:56 UTC www.airpower.maxwell.af.mil [Source type: FILTERED WITH BAYES]

^ Who needs a handheld Global Positioning System (GPS) device?
  • Global Positioning Systems: News & Videos about Global Positioning Systems - CNN.com 9 October 2009 7:11 UTC topics.edition.cnn.com [Source type: News]

.It provides reliable positioning, navigation, and timing services to worldwide users on a continuous basis in all weather, day and night, anywhere on or near the Earth which has an unobstructed view of four or more GPS satellites.^ The radio navigation is satellite based and provides a three dimensional position through out the day and night.
  • What Is GPS? - Blurtit 16 January 2010 16:26 UTC www.blurtit.com [Source type: General]

^ At least four of the space beacons are in view from any spot on Earth at any time.
  • Space Today Online - Satellites - NAVSTAR global positioning system GPS satellites 22 September 2009 23:43 UTC www.spacetoday.org [Source type: FILTERED WITH BAYES]

^ GPS and satellite navigation system .
  • Combining GPS with TOA/TDOA of ... - Google Patent Search 27 January 2010 23:56 UTC www.google.com [Source type: Reference]

.GPS is made up of three segments: Space, Control and User.^ GPS is built around three segments.
  • Search Results ((keywords_en:GLOBAL POSITIONING SYSTEM)) - ETH E-Collection 27 January 2010 23:56 UTC e-collection.ethbib.ethz.ch [Source type: Academic]

^ This organization includes three different segments namely the control segment, the user segment and the space segment.
  • GPS Greatest - Home 13 January 2010 11:56 UTC gpsgreatest.com [Source type: FILTERED WITH BAYES]

^ GPS consists of three segments: space, control, and user.
  • GPS Frequently Asked Questions - USCG Navigation Center 13 January 2010 11:56 UTC www.navcen.uscg.gov [Source type: Reference]

.The Space Segment is composed of 24 to 32 satellites in Medium Earth Orbit and also includes the boosters required to launch them into orbit.^ The space segment includes the GPS satellite constellation.
  • global positioning system « beehivepress.org 27 January 2010 23:56 UTC www.beehivepress.org [Source type: FILTERED WITH BAYES]

^ The space segment is based on the constellation of 24 active and 3 spare satellites orbiting the Earth.
  • Precision Farming Tools: Global Positioning System (GPS) - Virginia Cooperative Extension 27 January 2010 23:56 UTC www.ext.vt.edu [Source type: Reference]

^ The 24 satellites orbit the earth transmitting their time and position.
  • Global Positioning System - GPS Definition and Diagram 27 January 2010 23:56 UTC www.wirelessdictionary.com [Source type: Reference]

.The Control Segment is composed of a Master Control Station, an Alternate Master Control Station, and a host of dedicated and shared Ground Antennas and Monitor Stations.^ The Control Segment consists of a master control station in Colorado Springs, with five monitor stations and three ground antennas located throughout the world.
  • GPS Frequently Asked Questions - USCG Navigation Center 13 January 2010 11:56 UTC www.navcen.uscg.gov [Source type: Reference]

^ The Master Control and Monitor stations Control the satellite system.
  • GPS - THE REMARKABLE GLOBAL POSITIONING SYSTEM 27 January 2010 23:56 UTC www.ultralighthomepage.com [Source type: FILTERED WITH BAYES]

^ Satellites paths are monitored by ground stations.
  • The Global Positioning System (GPS) 27 January 2010 23:56 UTC physics.syr.edu [Source type: Academic]

.The User Segment is composed of hundreds of thousands of U.S. and allied military users of the secure GPS Precise Positioning Service, and tens of millions of civil, commercial and scientific users of the Standard Positioning Service (see GPS navigation devices).^ Global Positioning System (GPS) was developed for navigation and precise-positioning.
  • Cell Phone GPS Technology | Cell Phone Reviews, New Cell Phones, Cell Phone How To 13 January 2010 11:56 UTC www.611connect.com [Source type: FILTERED WITH BAYES]

^ See Standard Positioning Service The GPS positioning service available to all users.
  • Micro Modular Technologies - GPS and Wireless Modules - Support 27 January 2010 23:56 UTC www.micro-modular.com [Source type: Reference]

^ Standard Positioning Service (SPS) - The GPS positioning service available to all users.
  • Micro Modular Technologies - GPS and Wireless Modules - Support 27 January 2010 23:56 UTC www.micro-modular.com [Source type: Reference]

.GPS satellites broadcast signals from space that GPS receivers use to provide three-dimensional location (latitude, longitude, and altitude) plus precise time.^ A three-dimensional GPS position with attached features and attributes is provided.
  • GPS Basic Information for Educators 13 January 2010 11:56 UTC www.gps4educators.com [Source type: Reference]

^ The GPS receiver can use these signals to determine its distance from each of the satellites.
  • Global Positioning System - GPS Definition and Diagram 27 January 2010 23:56 UTC www.wirelessdictionary.com [Source type: Reference]
  • Global Positioning System (GPS), 2nd edition 27 January 2010 23:56 UTC www.althosbooks.com [Source type: Reference]

^ To "triangulate," a GPS receiver measures distance using the travel time of radio signals.
  • Tamil Nadu Forest Department 27 January 2010 23:56 UTC www.forests.tn.nic.in [Source type: FILTERED WITH BAYES]

.GPS has become a widely used aid to navigation worldwide, and a useful tool for map-making, land surveying, commerce, scientific uses, tracking and surveillance, and hobbies such as geocaching and waymarking.^ It is now a key tool for aiding navigation globally and an essential tool for activities such as land surveying, mapping, tele-coomunications and commerce.
  • GPS Systems For Sale - New & Used GPS Navigation Systems, Units, Accessories, Software at Just GPS Systems 13 January 2010 11:56 UTC www.justgpssystems.com [Source type: Academic]

^ Using a GPS tracking device on a car .
  • GPS Tracking : Tracking The World 13 January 2010 11:56 UTC trackingtheworld.com [Source type: General]

^ Since the first experimental satellite was launched in 1978, GPS has become an indispensable aid to navigation around the world, and an important tool for map-making and land surveying.
  • Reviews of GPS Systems and Software 13 January 2010 11:56 UTC www.gps-reviews.us [Source type: Reference]

.Also, the precise time reference is used in many applications including the scientific study of earthquakes and as a time synchronization source for cellular network protocols.^ GPS is also largely used in scientific study of earthquakes and in synchronization of telecommunication networks.
  • GPS Powers - Home 13 January 2010 11:56 UTC www.gpspowers.com [Source type: General]

^ Precise time reference .
  • GPS GLOBAL POSITIONING SYSTEM 27 January 2010 23:56 UTC www.speedace.info [Source type: FILTERED WITH BAYES]

^ GPS also provides a precise time reference used in many applications including scientific study of earthquakes, and synchronization of telecommunications networks.
  • Global Positioning System! 27 January 2010 23:56 UTC www.kipaddotta.com [Source type: FILTERED WITH BAYES]
  • Reviews of GPS Systems and Software 13 January 2010 11:56 UTC www.gps-reviews.us [Source type: Reference]

.GPS has become a mainstay of transportation systems worldwide, providing navigation for aviation, ground, and maritime operations.^ GPS and satellite navigation system .
  • Combining GPS with TOA/TDOA of ... - Google Patent Search 27 January 2010 23:56 UTC www.google.com [Source type: Reference]

^ GPS system for navigating a vehicle .
  • Global positioning system - Google Patent Search 27 January 2010 23:56 UTC www.google.com [Source type: Reference]

^ GPS car navigation systems (889) .
  • GPS Global Positioning System Manufacturers & Suppliers | Global Sources 27 January 2010 23:56 UTC www.globalsources.com [Source type: FILTERED WITH BAYES]

.Disaster relief and emergency services depend upon GPS for location and timing capabilities in their life-saving missions.^ GPS helps rescuers locate ships lost at sea and enables emergency crews on land to quickly find their way to the site of an accident or disaster.
  • GLOBAL POSITIONING SYSTEM (GPS), 27 January 2010 23:56 UTC www.history.com [Source type: FILTERED WITH BAYES]

^ The data supplied by the GPS is helpful in performing several techniques, procedures, and missions that require soldiers to know their exact location.
  • Reading Topographic Maps - How the Global Positioning System - GPS - Works 27 January 2010 23:56 UTC www.map-reading.com [Source type: FILTERED WITH BAYES]
  • SurvivalIQ Handbook: Land Navigation - Global positioning system 27 January 2010 23:56 UTC www.survivaliq.com [Source type: Reference]

^ The satellites which supply the navigation message and precise time , the basis of the GPS concept, are located 11,000 nautical mile s above the earth in a widely dispersed constellation.
  • Global Positioning System@Everything2.com 27 January 2010 23:56 UTC www.everything2.com [Source type: FILTERED WITH BAYES]

.The accurate timing that GPS provides facilitates everyday activities such as banking, mobile phone operations, and even the control of power grids.^ But you can't get such precise timing from a mobile GPS receiver.
  • Exploring GPS - 2003-09-22 00:00:00 | Design News 16 January 2010 16:26 UTC www.designnews.com [Source type: FILTERED WITH BAYES]

^ Below are mobile phones that offer A-GPS: .
  • Cell Phone GPS Technology | Cell Phone Reviews, New Cell Phones, Cell Phone How To 13 January 2010 11:56 UTC www.611connect.com [Source type: FILTERED WITH BAYES]

^ The GPS System operates on its own time system.
  • GPS - THE REMARKABLE GLOBAL POSITIONING SYSTEM 27 January 2010 23:56 UTC www.ultralighthomepage.com [Source type: FILTERED WITH BAYES]

.Farmers, surveyors, geologists and countless others perform their work more efficiently, safely, economically, and accurately using the free and open GPS signals.^ See other GPS uses here .
  • ForestPal.com 13 January 2010 11:56 UTC www.forestpal.com [Source type: FILTERED WITH BAYES]

^ Isn’t the GPS much more efficient and accurate?!
  • Portable GPS Navigator Store | The Best Independent Portable GPS Site 13 January 2010 11:56 UTC portablegpsnavigatorstore.com [Source type: General]

^ Then I got this gps, and it works perfectly for what I'm using it for.
  • Garmin eTrex H Handheld GPS Navigator 16 January 2010 16:26 UTC garmingpsnavigator.net [Source type: General]

Contents

History

.The design of GPS is based partly on similar ground-based radio navigation systems, such as LORAN and the Decca Navigator developed in the early 1940s, and used during World War II.^ GPS is often used by civilians as a navigation system.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]
  • GPS (Global Positioning System) - Mobile terms glossary - GSMArena.com 27 January 2010 23:56 UTC www1.gsmarena.com [Source type: General]

^ The goal was development of a space-based, highly accurate navigation system.
  • Contributions of the Global Positioning System 27 January 2010 23:56 UTC www.airpower.maxwell.af.mil [Source type: FILTERED WITH BAYES]

^ GPS and satellite navigation system .
  • Combining GPS with TOA/TDOA of ... - Google Patent Search 27 January 2010 23:56 UTC www.google.com [Source type: Reference]

.In 1956 Friedwardt Winterberg[1] proposed a test of General Relativity using accurate atomic clocks placed in orbit in artificial satellites.^ In addition, each satellite has an atomic clock inside of it.
  • Global Positioning System@Everything2.com 27 January 2010 23:56 UTC www.everything2.com [Source type: FILTERED WITH BAYES]

^ The general relativistic equations correcting signals of atomic clocks in satellites were first published in 1956 by Friedwardt Winterberg.

^ Most artificial satellites are orbiting the Earth.
  • The Global Positioning System 27 January 2010 23:56 UTC www.cfa.harvard.edu [Source type: FILTERED WITH BAYES]

.To achieve accuracy requirements, GPS uses principles of general relativity to correct the satellites' atomic clocks.^ Accuracy of GPS and DGPS and relative costs.
  • Precision Farming Tools: Global Positioning System (GPS) - Virginia Cooperative Extension 27 January 2010 23:56 UTC www.ext.vt.edu [Source type: Reference]

^ Correcting a GPS receiver's clock .
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ The receiver uses a fourth satellite to solve for x , y , z , and t which is used to correct the receiver's clock.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

Additional inspiration for the GPS came when the Soviet Union launched the first man-made satellite, Sputnik in 1957. A team of U.S. scientists led by Dr. Richard B. Kershner were monitoring Sputnik's radio transmissions. .They discovered that, because of the Doppler effect, the frequency of the signal being transmitted by Sputnik was higher as the satellite approached, and lower as it continued away from them.^ The Doppler effect ( define ) of the signal grew stronger as the satellite approached and grew weaker as it flew away.
  • What is a Global Positioning System (GPS)? 27 January 2010 23:56 UTC www.geeks.com [Source type: FILTERED WITH BAYES]

^ They discovered that, because of the Doppler effect , the frequency of the signal being transmitted by Sputnik was higher as the satellite approached, and lower as it continued away from them.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ They discovered that, because of the Doppler effect, the frequency of the signal being transmitted by Sputnik was higher as the satellite approached, and lower as it continued away from them.
  • Global Positioning System! 27 January 2010 23:56 UTC www.kipaddotta.com [Source type: FILTERED WITH BAYES]
  • Global Positioning System (GPS) - History, Facts and Pictures 27 January 2010 23:56 UTC www.aviationexplorer.com [Source type: Reference]
  • Ideal GPS Systems 16 January 2010 16:26 UTC www.idealgpssystems.com [Source type: General]

.They realized that since they knew their exact location on the globe, they could pinpoint where the satellite was along its orbit by measuring the Doppler distortion (see Transit (satellite)).^ Each satellite transmits its exact location along with a timed reference signal.
  • Global Positioning System - GPS Definition and Diagram 27 January 2010 23:56 UTC www.wirelessdictionary.com [Source type: Reference]
  • Global Positioning System (GPS), 2nd edition 27 January 2010 23:56 UTC www.althosbooks.com [Source type: Reference]

^ They realized that since they knew their exact location on the globe, they could pinpoint where the satellite was along its orbit by measuring the Doppler distortion.
  • GPS GLOBAL POSITIONING SYSTEM 27 January 2010 23:56 UTC www.speedace.info [Source type: FILTERED WITH BAYES]
  • Global Positioning System! 27 January 2010 23:56 UTC www.kipaddotta.com [Source type: FILTERED WITH BAYES]
  • Global Positioning System (GPS) - History, Facts and Pictures 27 January 2010 23:56 UTC www.aviationexplorer.com [Source type: Reference]
  • Ideal GPS Systems 16 January 2010 16:26 UTC www.idealgpssystems.com [Source type: General]

^ By knowing the precise locations of the satellites at any given moment, the receiver uses trilateration, the navigation technique of ship captains for centuries, to pinpoint its own location.
  • EETimes Encyclopedia 13 January 2010 11:56 UTC www.eetimes.com [Source type: FILTERED WITH BAYES]
  • TechOnline | TechOnline - Encyclopedia 13 January 2010 11:56 UTC www.techonline.com [Source type: FILTERED WITH BAYES]

.The first satellite navigation system, Transit, used by the United States Navy, was first successfully tested in 1960. It used a constellation of five satellites and could provide a navigational fix approximately once per hour.^ GALILEO - European satellite navigation system.

^ GPS and satellite navigation system .
  • Combining GPS with TOA/TDOA of ... - Google Patent Search 27 January 2010 23:56 UTC www.google.com [Source type: Reference]

^ Navman S200 satellite navigation system .
  • Global Positioning Systems (GPS) in Electronics - Compare prices at BizRate UK! 9 October 2009 7:11 UTC www.bizrate.co.uk [Source type: General]

.In 1967, the U.S. Navy developed the Timation satellite which proved the ability to place accurate clocks in space, a technology that GPS relies upon.^ In space, satellites and spacecraft rely on GPS to determine their position and orientation.
  • GLOBAL POSITIONING SYSTEM (GPS), 27 January 2010 23:56 UTC www.history.com [Source type: FILTERED WITH BAYES]

^ In 1967, the U.S. Navy developed the Timation satellite which proved the ability to place accurate clocks in space, a technology that GPS relies upon.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ In 1967, the U.S. Navy developed the Timation satellite which proved the ability to place accurate clocks in space, a technology the GPS system relies upon.
  • Global Positioning System! 27 January 2010 23:56 UTC www.kipaddotta.com [Source type: FILTERED WITH BAYES]

.In the 1970s, the ground-based Omega Navigation System, based on phase comparison of signal transmission from pairs of stations,[2] became the first worldwide radio navigation system.^ In the 1970s, the ground-based Omega Navigation System, based on signal phase comparison, became the first world-wide radio navigation system.
  • GPS GLOBAL POSITIONING SYSTEM 27 January 2010 23:56 UTC www.speedace.info [Source type: FILTERED WITH BAYES]
  • Global Positioning System! 27 January 2010 23:56 UTC www.kipaddotta.com [Source type: FILTERED WITH BAYES]

^ The GPS is a satellite-based, radio navigational system.
  • Reading Topographic Maps - How the Global Positioning System - GPS - Works 27 January 2010 23:56 UTC www.map-reading.com [Source type: FILTERED WITH BAYES]
  • SurvivalIQ Handbook: Land Navigation - Global positioning system 27 January 2010 23:56 UTC www.survivaliq.com [Source type: Reference]

^ In the 1970s, the ground-based Omega Navigation System, based on signal phase comparison, became the first worldwide radio navigation system.

.However, limitations of these systems drove the need for a more universal navigation solution with greater accuracy.^ If you are interested in learning more about the GPS Navigation Systems , you can refer to an excellent resource available on Wikipedia here.
  • GPS Systems For Sale - New & Used GPS Navigation Systems, Units, Accessories, Software at Just GPS Systems 13 January 2010 11:56 UTC www.justgpssystems.com [Source type: Academic]

^ He continued with, "In the U.S. there are more than 300M vehicles and only 9% of them currently have a navigation system in place.
  • NavStar Technologies, Inc. Completes Reverse Merger with European Diversified Holdings Company. | Company Activities & Management > Company Structures & Ownership from AllBusiness.com 22 September 2009 23:43 UTC www.allbusiness.com [Source type: News]

^ For example, such a global positioning system may be a Global Positioning System, a Global Navigation Satellite System, a Galileo system, a Glonas system, any other navigation system that relies on the resolution of time as part of a position solution, or a combination of the above systems.
  • METHOD AND APPARATUS FOR CALIBRATING A GLOBAL POSITIONING SYSTEM OSCILLATOR - Patent application 27 January 2010 23:56 UTC www.faqs.org [Source type: Reference]

.While there were wide needs for accurate navigation in military and civilian sectors, almost none of those were seen as justification for the billions of dollars it would cost in research, development, deployment and operation for a complex constellation of navigation satellites.^ It is the only operational satellite navigation system.
  • global positioning system « beehivepress.org 27 January 2010 23:56 UTC www.beehivepress.org [Source type: FILTERED WITH BAYES]

^ It is a satellite-based navigation system developed and introduced by the U.S. military in the 1990s.
  • What Is GPS? - Blurtit 16 January 2010 16:26 UTC www.blurtit.com [Source type: General]

^ Payload: Two L-Band navigation signals at 1575.42 MHz (L1) and 1227.60 MHz (L2) Financial/Operational: Block I satellite cost was $ 20 million each.

.However during the Cold War arms race, the nuclear threat to the very existence of the United States was the one need that did justify this cost in the view of the US Congress.^ I mean, the Soviets, despite being the alleged evil empire, did prompt us to shift into gear on more than one occasion.
  • gps Articles, Posts, Blogs, Videos - Technorati 13 January 2010 11:56 UTC technorati.com [Source type: General]

^ When I spent $2200 on this useless hunk of junk, I thought I was getting the state of the art, all-in-one head unit.
  • Discount GPS Navigation - Global Positioning Systems from Garmin & Magellan 9 October 2009 7:11 UTC www.smarter.com [Source type: General]

^ In practice, in view of the hazards and costs this would induce for US and foreign shipping, it is unlikely to be reintroduced, and various government agencies, including the FAA, have stated that it is not intended to be reintroduced.
  • Global Positioning System! 27 January 2010 23:56 UTC www.kipaddotta.com [Source type: FILTERED WITH BAYES]

And this deterrent effect is why GPS was funded. .The nuclear triad consisted of the US Navy's Submarine Launched Ballistic Missiles (SLBMs) along with the US Air Force's strategic bombers and Intercontinental Ballistic Missiles (ICBMs).^ They knew target coordinates, ballistics, and missile trajectory but the essential element in the fire control solution was current submarine coordinates.
  • GPS Basic Information for Educators 13 January 2010 11:56 UTC www.gps4educators.com [Source type: Reference]

^ To the contrary, the ‘U.S. Strategic Command and Air Force Space Command’ (AFSPC) along with STRATCOM have announced improvements “that benefits not only military operations, but also all GPS users by taking advantage of the largest on-orbit GPS constellation in its history” .
  • GPS Review : GPS Reviews 13 January 2010 11:56 UTC www.gpsreview.net [Source type: General]

^ The flight paths of the satellites are tracked by US Air Force monitoring stations in Hawaii, Kwajalein, Ascension Island, Diego Garcia, and Colorado Springs, Colorado, along with monitor stations operated by the National Geospatial-Intelligence Agency (NGA).
  • Global Positioning System! 27 January 2010 23:56 UTC www.kipaddotta.com [Source type: FILTERED WITH BAYES]

.Considered vital to the nuclear deterrence posture, accurate determination of the SLBM launch position was a force multiplier.^ It was originally designed jointly by the U.S. Navy and the U.S. Air Force to permit the determination of position and time for military troops and guided missiles.
  • The Global Positioning System: a detailed lookedat the miracle of modern navigation; by Robert A. Nelson 27 January 2010 23:56 UTC www.aticourses.com [Source type: FILTERED WITH BAYES]

^ The Global Positioning System can be used for determining someone else’s definite location that provides a highly accurate time reference almost anywhere on Earth.
  • global positioning system « beehivepress.org 27 January 2010 23:56 UTC www.beehivepress.org [Source type: FILTERED WITH BAYES]

^ The ability to accurately determine position location has always been a major problem for soldiers.
  • Reading Topographic Maps - How the Global Positioning System - GPS - Works 27 January 2010 23:56 UTC www.map-reading.com [Source type: FILTERED WITH BAYES]

.Precise navigation would enable US submarines to get an accurate fix of their positions prior to launching their SLBMs.^ It is a navigation and precise-positioning tool.
  • Nextar - Support 13 January 2010 11:56 UTC www.nextar.com [Source type: FILTERED WITH BAYES]

^ This enables the GPS receivers to compute their time, location and velocity precisely, aiding in their navigation.
  • GPS Systems For Sale - New & Used GPS Navigation Systems, Units, Accessories, Software at Just GPS Systems 13 January 2010 11:56 UTC www.justgpssystems.com [Source type: Academic]

^ GPS Development In the late 1950s, scientists at John Hopkins University developed a way to use radio signals originating from a satellite in space to provide accurate position updates to navigation equipment located on the US Navys ships and submarines.

[3] .The US Air Force with two-thirds of the nuclear triad also had requirements for a more accurate and reliable navigation system.^ The US Air Force is designated as the executive service for system management.

^ If you are interested in learning more about the GPS Navigation Systems , you can refer to an excellent resource available on Wikipedia here.
  • GPS Systems For Sale - New & Used GPS Navigation Systems, Units, Accessories, Software at Just GPS Systems 13 January 2010 11:56 UTC www.justgpssystems.com [Source type: Academic]

^ Bradford Parkinson, professor of aeronautics and astronautics at Stanford University, conceived the present satellite-based system in the early 1960s and developed it in conjunction with the U.S. Air Force.
  • Global Positioning System! 27 January 2010 23:56 UTC www.kipaddotta.com [Source type: FILTERED WITH BAYES]

.The Navy and Air Force were developing their own technologies in parallel to solve what was essentially the same problem.^ Bradford Parkinson, professor of aeronautics and astronautics at Stanford University, conceived the present satellite-based system in the early 1960s and developed it in conjunction with the U.S. Air Force.
  • Global Positioning System! 27 January 2010 23:56 UTC www.kipaddotta.com [Source type: FILTERED WITH BAYES]

^ As Easton said in his acceptance speech for the Magellanic Premium, “On the Labor Day weekend, 1973, the Air Force accepted the Navy technology for satellite positioning, and here I salute Dr. Parkinson for knowing a good technology when he sees it.” .
  • The Space Review: Who invented the Global Positioning System? 27 January 2010 23:56 UTC www.thespacereview.com [Source type: FILTERED WITH BAYES]

^ Bradford Parkinson , professor of aeronautics and astronautics at Stanford University , conceived the present satellite-based system in the early 1960s and developed it in conjunction with the U.S. Air Force.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

.To increase the survivability of ICBMs, there was a proposal to use mobile launch platforms so the need to fix the launch position had similarity to the SLBM situation.^ Other similar systems are the Russian GLONASS (incomplete as of 2008), the upcoming European Galileo positioning system, the proposed COMPASS navigation system of China, and IRNSS of India.
  • Global Positioning System (GPS) - History, Facts and Pictures 27 January 2010 23:56 UTC www.aviationexplorer.com [Source type: Reference]

^ Remember how the first gen iPhone (and similar non-GPS devices) use Wi-Fi nodes to guesstimate the user's position?
  • GPS - Gizmodo 16 January 2010 16:26 UTC tags.gizmodo.com [Source type: General]

^ You can use these features for a security purpose and other purpose which needs remote positioning such as asset protection and tracking.
  • miniHomer GPS Position Finder, BackTrack, Guider 16 January 2010 16:26 UTC www.berlinkauf.com [Source type: FILTERED WITH BAYES]

.In 1960, the Air Force proposed a radio-navigation system called MOSAIC (Mobile System for Accurate ICBM Control) that was essentially a 3-D LORAN.^ MOSAIC (Mobile System for Accurate ICBM Control) was first proposed to the Air Force by Getting and his colleague Shep Arkin on May 11, 1960.
  • Charting a Course Toward Global Navigation 22 September 2009 23:43 UTC www.aero.org [Source type: Academic]

^ Radio frequency control system .
  • Vehicle global positioning system (US5971552) 27 January 2010 23:56 UTC www.delphion.com [Source type: Academic]

^ Bradford Parkinson, professor of aeronautics and astronautics at Stanford University, conceived the present satellite-based system in the early 1960s and developed it in conjunction with the U.S. Air Force.
  • Global Positioning System! 27 January 2010 23:56 UTC www.kipaddotta.com [Source type: FILTERED WITH BAYES]

.A follow-on study called Project 57 was worked in 1963 and it was "in this study that the GPS concept was born."^ To describe the basic concept of how a GPS receiver works, the errors are at first ignored.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ In 1963, the Space Division of the Air Force began supporting this study, known as Project 621B, and requested that Aerospace continue its work on determining navigation coordinates from satellite signals.
  • Charting a Course Toward Global Navigation 22 September 2009 23:43 UTC www.aero.org [Source type: Academic]

^ The Project 57 study was directed by Phillip Diamond of the Systems Planning Division, and, as Getting noted, it was "in this study that the GPS concept was born."
  • Charting a Course Toward Global Navigation 22 September 2009 23:43 UTC www.aero.org [Source type: Academic]

.That same year the concept was pursued as Project 621B, which had "many of the attributes that you now see in GPS"[4] and promised increased accuracy for Air Force bombers as well as ICBMs.^ How do we increase GPS accuracy?
  • Precision Farming Tools: Global Positioning System (GPS) - Virginia Cooperative Extension 27 January 2010 23:56 UTC www.ext.vt.edu [Source type: Reference]

^ According to Parkinson, Project 621B had "many of the attributes that you now see in GPS. It has probably never been given its due credit."
  • Charting a Course Toward Global Navigation 22 September 2009 23:43 UTC www.aero.org [Source type: Academic]

^ If you are wondering Where to buy GPS Systems , buyagpssystem.com is an excellent source.The GPS system was first conceived by the U.S. Department of Defense and was first invented to assist the operations of the United States Air Force.

.Updates from the Navy Transit system were too slow for the high speeds that the Air Force operated at.^ Bradford Parkinson, professor of aeronautics and astronautics at Stanford University, conceived the present satellite-based system in the early 1960s and developed it in conjunction with the U.S. Air Force.
  • Global Positioning System! 27 January 2010 23:56 UTC www.kipaddotta.com [Source type: FILTERED WITH BAYES]

^ If you are wondering Where to buy GPS Systems , buyagpssystem.com is an excellent source.The GPS system was first conceived by the U.S. Department of Defense and was first invented to assist the operations of the United States Air Force.

^ The Transit system was too slow and too intermittent to keep up with the high speeds of airplanes, and the Air Force hoped to obtain an accuracy of 15 meters—much better than what Transit was providing for ships.
  • Charting a Course Toward Global Navigation 22 September 2009 23:43 UTC www.aero.org [Source type: Academic]

.The Navy Research Laboratory continued advancements with their Timation (Time Navigation) satellites, first launched in 1967, and with the third one in 1974 carrying the first atomic clock put into orbit.^ First GPS satellite was launched in 1978.
  • Precision Farming Tools: Global Positioning System (GPS) - Virginia Cooperative Extension 27 January 2010 23:56 UTC www.ext.vt.edu [Source type: Reference]

^ Only one clock is in use on each satellite at a time.

^ The first IIR satellite to reach orbit was also launched in 1997.
  • The Global Positioning System: a detailed lookedat the miracle of modern navigation; by Robert A. Nelson 27 January 2010 23:56 UTC www.aticourses.com [Source type: FILTERED WITH BAYES]

[5]
.
With these parallel developments out of the 1960s, it was realized that a superior system could be developed by synthesizing the best technologies from 621B, Transit, Timation and SECOR in a multi-service program.
^ Bradford Parkinson, professor of aeronautics and astronautics at Stanford University, conceived the present satellite-based system in the early 1960s and developed it in conjunction with the U.S. Air Force.
  • Global Positioning System! 27 January 2010 23:56 UTC www.kipaddotta.com [Source type: FILTERED WITH BAYES]

^ Bradford Parkinson , professor of aeronautics and astronautics at Stanford University , conceived the present satellite-based system in the early 1960s and developed it in conjunction with the U.S. Air Force.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ In 1967, the U.S. Navy developed the Timation satellite which proved the ability to place accurate clocks in space, a technology the GPS relies upon.
  • Global Positioning System (GPS) - History, Facts and Pictures 27 January 2010 23:56 UTC www.aviationexplorer.com [Source type: Reference]

.Over the Labor Day weekend in 1973, a meeting of about 12 military officers at the Pentagon discussed the creation of a Defense Navigation Satellite System (DNSS).^ GALILEO - European satellite navigation system.

^ GPS and satellite navigation system .
  • Combining GPS with TOA/TDOA of ... - Google Patent Search 27 January 2010 23:56 UTC www.google.com [Source type: Reference]

^ The Global Positioning System is a satellite navigation system.
  • The Social Effects of the Global Positioning System - a knol by Anonymous 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

.It was at this meeting that "the real synthesis that became GPS was created."^ It was at this meeting, he said, that "the real synthesis that became GPS was created."
  • Charting a Course Toward Global Navigation 22 September 2009 23:43 UTC www.aero.org [Source type: Academic]

^ The ability to create the synthesis that became GPS and build the system remains Parkinson's outstanding achievement as program manager.
  • Charting a Course Toward Global Navigation 22 September 2009 23:43 UTC www.aero.org [Source type: Academic]

^ You've always been able to edit the HTML source of Google Maps created by GPS Visualizer to make them meet your specifications, but it's much easier now.

.Later that year, the DNSS program was named Navstar.^ More NAVSTARs have been launched in later years.
  • Space Today Online - Satellites - NAVSTAR global positioning system GPS satellites 22 September 2009 23:43 UTC www.spacetoday.org [Source type: FILTERED WITH BAYES]

^ There will be considerable more information provided on coordinate datums in the later years of the geomatics program.

.With the individual satellites being associated with the name Navstar (as with the predecessors Transit and Timation), a more fully encompassing name was used to identify the constellation of Navstar satellites.^ Navstar The name give to GPS satellites.
  • GPS Basic Information for Educators 13 January 2010 11:56 UTC www.gps4educators.com [Source type: Reference]

^ Using a constellation of five satellites, it could provide a navigational fix approximately once per hour.
  • GPS GLOBAL POSITIONING SYSTEM 27 January 2010 23:56 UTC www.speedace.info [Source type: FILTERED WITH BAYES]
  • Global Positioning System! 27 January 2010 23:56 UTC www.kipaddotta.com [Source type: FILTERED WITH BAYES]
  • Global Positioning System (GPS) - History, Facts and Pictures 27 January 2010 23:56 UTC www.aviationexplorer.com [Source type: Reference]
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]
  • Ideal GPS Systems 16 January 2010 16:26 UTC www.idealgpssystems.com [Source type: General]

^ Just as America's earlier satellite navigation system known as Transit gave more-precise location fixes than the Loran non-satellite navigation system on the ground, NAVSTAR gives more-precise location fixes more frequently than Transit.
  • Space Today Online - Satellites - NAVSTAR global positioning system GPS satellites 22 September 2009 23:43 UTC www.spacetoday.org [Source type: FILTERED WITH BAYES]

This more complete name was Navstar-GPS which was later shortened simply to GPS.[6]
.After Korean Air Lines Flight 007 was shot down in 1983 after straying into the USSR's prohibited airspace,[7] President Ronald Reagan issued a directive making GPS freely available for civilian use, once it was sufficiently developed, as a common good.^ In 1983, after Soviet interceptor aircraft shot down the civilian airliner KAL 007 that strayed into prohibited airspace due to navigational errors, killing all 269 people on board, U.S. President Ronald Reagan announced that the GPS would be made available for civilian uses once it was completed.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ Despite these costs, GPS is free for civilian use as a public good.
  • Global Positioning System! 27 January 2010 23:56 UTC www.kipaddotta.com [Source type: FILTERED WITH BAYES]

^ Korean Air Flight 007 .
  • Global Positioning System@Everything2.com 27 January 2010 23:56 UTC www.everything2.com [Source type: FILTERED WITH BAYES]

[8] The first satellite was launched in 1989, and the 24th and last satellite was launched in 1994.
.Initially, the highest quality signal was reserved for military use, and the signal available for civilian use intentionally degraded ("Selective Availability", SA).^ Selective Availability (SA) is the intentional degradation of the SPS signals by a time varying bias.
  • Unit 017 - Global Positioning System Overview 27 January 2010 23:56 UTC www.ncgia.ucsb.edu [Source type: Reference]

^ Initially the highest quality signal was reserved for military use, while the signal available for civilian use was intentionally degraded (”Selective Availability”, SA).

^ SA Selective Availability is the artificial degradation of the satellite signal by the Department of Defense.
  • GPS Basic Information for Educators 13 January 2010 11:56 UTC www.gps4educators.com [Source type: Reference]

.This changed in 2000, with U.S. President Bill Clinton ordering Selective Availability (SA) turned off at midnight May 1, 2000, improving the precision of civilian GPS from about 1000 feet to about 65 feet.^ Under pressure from civilian organizations, U.S. President William J. Clinton in May 2000 ordered the selective availability function turned off.
  • Space Today Online - Satellites - NAVSTAR global positioning system GPS satellites 22 September 2009 23:43 UTC www.spacetoday.org [Source type: FILTERED WITH BAYES]

^ The government turned off SA in May 2000, which significantly improved the accuracy of civilian GPS receivers.
  • How does the Global Positioning System (GPS) work ? 27 January 2010 23:56 UTC www.pocketgpsworld.com [Source type: General]

^ GPS accuracy (since 1 May 2000).
  • What is GPS? An explanation into Global Positioning Systems 27 January 2010 23:56 UTC www.ja-gps.com.au [Source type: FILTERED WITH BAYES]

Timeline and modernization

.
Summary of satellites[9]
Block Launch
Period
Satellite launches Currently in orbit
and healthy
Suc-
cess
Fail-
ure
In prep-
aration
Plan-
ned
I 1978–1985 10 1 0 0 0
II 1989–1990 9 0 0 0 0
IIA 1990–1997 19 0 0 0 11 of the 19 launched
IIR 1997–2004 12 1 0 0 12 of the 13 launched
IIR-M 2005–2009 8 0 0 0 7 of the 8 launched
IIF 2010–2011 0 0 10 0 0
IIIA 2014–? 0 0 0 12 0
IIIB 0 0 0 8 0
IIIC 0 0 0 16 0
Total 58 2 10 36 30
(Last update: 29 December 2009)
.PRN 01 from Block IIR-M is unhealthy
PRN 25 from Block IIA is unhealthy
See the GPS almanac.
^ GPS Block IIR production no.

^ Because of this, carrier frequency tracking along with PRN code tracking are used to determine when the received satellite's PRN code begins (see "How a GPS Receiver Gets a Lock" ).
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ See Details from $2,134 25 offers Marine GPS, Fixed, 1500 Waypoints, WAAS enabled Garmin GPSMAP 4212 GPS Receiver $118 - $350 .
  • GPS Devices Handheld Electronics - Find great deals, lowest prices, and buy GPS Devices Handheld Electronics at Shopping.com 13 January 2010 11:56 UTC www.shopping.com [Source type: General]

For a more complete list, see list of GPS satellite launches
  • In 1972, the U.S. Air Force Central Inertial Guidance Test Facility (Holloman AFB), conducted developmental flight tests of two prototype GPS receivers over White Sands Missile Range, using ground-based pseudo-satellites.
  • In 1978, the first experimental Block-I GPS satellite was launched.
  • In 1983, after Soviet interceptor aircraft shot down the civilian airliner KAL 007 that strayed into prohibited airspace due to navigational errors, killing all 269 people on board, U.S. President Ronald Reagan announced that the GPS would be made available for civilian uses once it was completed.^ In 1983, after Soviet interceptor aircraft shot down the civilian airliner KAL 007 that strayed into prohibited airspace due to navigational errors, killing all 269 people on board, U.S. President Ronald Reagan announced that the GPS would be made available for civilian uses once it was completed.
    • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

    ^ GPS is often used by civilians as a navigation system.
    • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]
    • GPS (Global Positioning System) - Mobile terms glossary - GSMArena.com 27 January 2010 23:56 UTC www1.gsmarena.com [Source type: General]

    ^ GPS and satellite navigation system .
    • Combining GPS with TOA/TDOA of ... - Google Patent Search 27 January 2010 23:56 UTC www.google.com [Source type: Reference]

    [10][11]
  • .
  • By 1985, ten more experimental Block-I satellites had been launched to validate the concept.
  • On February 14, 1989, the first modern Block-II satellite was launched.
  • In 1992, the 2nd Space Wing, which originally managed the system, was de-activated and replaced by the 50th Space Wing.
  • By December 1993, the GPS achieved initial operational capability.^ The satellite constellation is managed by the United States Air Force 50th Space Wing.
    • Global Positioning System! 27 January 2010 23:56 UTC www.kipaddotta.com [Source type: FILTERED WITH BAYES]

    ^ Artist's conception of GPS satellite in orbit .
    • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

    ^ In 1992, the 2nd Space Wing, which originally managed the system, was de-activated and replaced by the 50th Space Wing .
    • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

    [12]
  • .
  • By January 17, 1994 a complete constellation of 24 satellites was in orbit.
  • Full Operational Capability was declared by NAVSTAR in April 1995.
  • In 1996, recognizing the importance of GPS to civilian users as well as military users, U.S. President Bill Clinton issued a policy directive[13] declaring GPS to be a dual-use system and establishing an Interagency GPS Executive Board to manage it as a national asset.
  • In 1998, U.S. Vice President Al Gore announced plans to upgrade GPS with two new civilian signals for enhanced user accuracy and reliability, particularly with respect to aviation safety and in 2000 the U.S. Congress authorized the effort, referring to it as GPS III.
  • In 1998, GPS technology was inducted into the Space Foundation Space Technology Hall of Fame.
  • On May 2, 2000 "Selective Availability" was discontinued as a result of the 1996 executive order, allowing users to receive a non-degraded signal globally.
  • In 2004, the United States Government signed an agreement with the European Community establishing cooperation related to GPS and Europe's planned Galileo system.
  • In 2004, U.S. President George W. Bush updated the national policy and replaced the executive board with the National Executive Committee for Space-Based Positioning, Navigation, and Timing.
  • November 2004, QUALCOMM announced successful tests of assisted GPS for mobile phones.^ System for measuring position by using global positioning system and receiver for global position system .
    • Combining GPS with TOA/TDOA of ... - Google Patent Search 27 January 2010 23:56 UTC www.google.com [Source type: Reference]

    ^ Constellation- The set of GPS satellites in orbit.
    • Micro Modular Technologies - GPS and Wireless Modules - Support 27 January 2010 23:56 UTC www.micro-modular.com [Source type: Reference]

    ^ GALILEO - European satellite navigation system.

    [14]
  • .
  • In 2005, the first modernized GPS satellite was launched and began transmitting a second civilian signal (L2C) for enhanced user performance.
  • On September 14, 2007, the aging mainframe-based Ground Segment Control System was transitioned to the new Architecture Evolution Plan.^ GPS satellites transmit two radio signals.
    • How does the Global Positioning System (GPS) work ? 27 January 2010 23:56 UTC www.pocketgpsworld.com [Source type: General]

    ^ On September 14, 2007, the aging mainframe-based Ground Segment Control System was transitioned to the new Architecture Evolution Plan.
    • Global Positioning System! 27 January 2010 23:56 UTC www.kipaddotta.com [Source type: FILTERED WITH BAYES]
    • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

    ^ GPS and satellite navigation system .
    • Combining GPS with TOA/TDOA of ... - Google Patent Search 27 January 2010 23:56 UTC www.google.com [Source type: Reference]

    [15]
  • The most recent launch was on August 17, 2009.[16] The oldest GPS satellite still in operation was launched on November 26, 1990, and became operational on December 10, 1990.[17]
  • On May 19, 2009, the U. S. Government Accountability Office issued a report warning that some GPS satellites could fail as soon as 2010.[18]
  • On May 21, 2009, the Air Force Space Command allayed fears of GPS system failure saying "There's only a small risk we will not continue to exceed our performance standard."[19]

Basic concept of GPS

.A GPS receiver calculates its position by precisely timing the signals sent by the GPS satellites high above the Earth.^ Let and denote the true coordinates of GPS receiver position at time, .
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ From this, it can determine the delay between the time the signal was sent and the time it was received with fairly good precision.
  • Global Positioning System@Everything2.com 27 January 2010 23:56 UTC www.everything2.com [Source type: FILTERED WITH BAYES]

^ Signals from multiple satellites are required to calculate a position .
  • How does the Global Positioning System (GPS) work ? 27 January 2010 23:56 UTC www.pocketgpsworld.com [Source type: General]

Each satellite continually transmits messages which include
  • the time the message was transmitted
  • precise orbital information (the ephemeris)
  • the general system health and rough orbits of all GPS satellites (the almanac).
.The receiver utilizes the messages it receives to determine the transit time of each message and computes the distances to each satellite.^ Knowing the indicated time the message was received , the GPS receiver can compute the indicated transit time, .
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ Using messages received from four satellites, the GPS receiver is able to determine the satellite positions and time sent.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ The receiver measures the transit time of each message and computes the distance to each satellite.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

.These distances along with the satellites' locations are used with the possible aid of trilateration to compute the position of the receiver.^ Aiding location determinations in satellite positioning system receivers .
  • Combining GPS with TOA/TDOA of ... - Google Patent Search 27 January 2010 23:56 UTC www.google.com [Source type: Reference]

^ Geometric trilateration is used to combine these distances with the location of the satellites to determine the receiver's location.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ The receiver measures the transit time of each message and computes the distance to each satellite.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

.This position is then displayed, perhaps with a moving map display or latitude and longitude; elevation information may be included.^ The position is displayed, perhaps with a moving map display or latitude and longitude; elevation information may be included.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ The result is provided in the form of a geographic position - longitude and latitude - to, for most receivers, within an accuracy of 10 to 100 meters.
  • GPS (Global Positioning System) - Mobile terms glossary - GSMArena.com 27 January 2010 23:56 UTC www1.gsmarena.com [Source type: General]

^ The initial position is a longitude of 118° West and a latitude of 34° North, which is around Los Angeles.
  • Attitude determination using a global positioning system - Patent 6580389 27 January 2010 23:56 UTC www.freepatentsonline.com [Source type: Reference]

.The GPS signal allows to repeat this calculation every 6 seconds.^ It is transmitted by each GPS satellite every 30 seconds to allow calculation of the satellite's position in space.
  • Micro Modular Technologies - GPS and Wireless Modules - Support 27 January 2010 23:56 UTC www.micro-modular.com [Source type: Reference]

^ GPS Area Calculation   -  http://www.gpsmeter.com/ Offers a program that allows the user to measure areas of any geometry, distances and to mark fix points.
  • Google Directory - Shopping > Consumer Electronics > Communications > Global Positioning System 27 January 2010 23:56 UTC directory.google.com [Source type: Reference]
  • Google Directory - Shopping > Consumer Electronics > Communications > Global Positioning System 27 January 2010 23:56 UTC dir.google.com [Source type: Reference]

^ A secondary motion detection system allows offender tracking in the absence of GPS signals.
  • iSecureTrac Systems & Services 13 January 2010 11:56 UTC www.isecuretrac.com [Source type: FILTERED WITH BAYES]

.Many GPS units show derived information such as direction and speed, calculated from position changes.^ GPS Calculating positions .
  • Global Positioning System! 27 January 2010 23:56 UTC www.kipaddotta.com [Source type: FILTERED WITH BAYES]

^ Many GPS units also show derived information such as direction and speed, calculated from position changes.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ Many data fields, such as elevation, display units of information.
  • SurvivalIQ Handbook: Land Navigation - Precision lightweight global positioning system receiver 27 January 2010 23:56 UTC www.survivaliq.com [Source type: Reference]

.Three satellites might seem enough to solve for position, since space has three dimensions and a position on the Earth's surface can be assumed.^ It might seem three satellites are enough to solve for position, since space has three dimensions.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ To compute a positions in three dimensions.
  • GIS Tutorials: Global Positioning System 27 January 2010 23:56 UTC www.gisdevelopment.net [Source type: FILTERED WITH BAYES]

^ Four satellites allow computation of three position dimensions and time.
  • Unit 017 - Global Positioning System Overview 27 January 2010 23:56 UTC www.ncgia.ucsb.edu [Source type: Reference]

.However, even a very small clock error multiplied by the very large speed of light[20]—the speed at which satellite signals propagate—results in a large positional error.^ Because of the very large value of the speed of light , c , the estimated distances from the GPS receiver to the satellites, the pseudoranges, are very sensitive to errors in the GPS receiver clock.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ Since GPS signals propagate at the speed of light , this represents an error of about 3 meters.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ However a very small clock error multiplied by the very large speed of light —the speed at which satellite signals propagate—results in a large positional error.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

.Therefore receivers use four or more satellites to solve for the receiver's location and time.^ A fourth satellite is received for a reference time.
  • Space Today Online - Satellites - NAVSTAR global positioning system GPS satellites 22 September 2009 23:43 UTC www.spacetoday.org [Source type: FILTERED WITH BAYES]

^ Using messages received from four satellites, the GPS receiver is able to determine the satellite positions and time sent.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ A typical GPS receiver calculates its position using the signals from four or more GPS satellites.
  • Global Positioning System (GPS) - History, Facts and Pictures 27 January 2010 23:56 UTC www.aviationexplorer.com [Source type: Reference]

.The very accurately computed time is effectively hidden by most GPS applications, which use only the location.^ To measure travel time, the GPS need a very accurate clock.
  • GIS Tutorials: Global Positioning System 27 January 2010 23:56 UTC www.gisdevelopment.net [Source type: FILTERED WITH BAYES]

^ While most GPS applications use the computed location only and effectively hide the very accurately computed time, it is used in a few specialized GPS applications such as time transfer and traffic signal timing.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ This antenna is mounted on the roof of a hut containing a scientific experiment needing precise timing.Many civilian applications benefit from GPS signals, using one or more of three basic components of the GPS; absolute location, relative movement, time transfer.
  • Global Positioning System! 27 January 2010 23:56 UTC www.kipaddotta.com [Source type: FILTERED WITH BAYES]

.A few specialized GPS applications do however use the time; these include time transfer, traffic signal timing, and synchronization of cell phone base stations.^ GPS is a satellite-based positioning system used for navigation, relative positioning, and time transfer.
  • Magellan GPS Receiver, Global Positioning Systems, Geodetic Base Station Software, Differential GPS 9 October 2009 7:11 UTC www.idsemergencymanagement.com [Source type: FILTERED WITH BAYES]

^ While most GPS applications use the computed location only and effectively hide the very accurately computed time, it is used in a few specialized GPS applications such as time transfer and traffic signal timing.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ At that time, however, it was mostly used by the military.
  • News - GPS - NAVIGATION - SYSTEM - GPS navigation 16 January 2010 16:26 UTC pl-gps.com [Source type: General]

.Although four satellites are required for normal operation, fewer apply in special cases.^ Although four satellites are required for normal operation, fewer may be needed in some special cases.
  • Global Positioning System (GPS) - History, Facts and Pictures 27 January 2010 23:56 UTC www.aviationexplorer.com [Source type: Reference]

^ Although four satellites are required for normal operation, fewer apply in special cases.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ When operated outside of SBAS coverage, a minimum of four satellites with acceptable geometry or three satellites plus calibrated barometric altitude are required in order to calculate a navigation solution.
  • GPS-4000S: Global Positioning System Sensor 27 January 2010 23:56 UTC www.rockwellcollins.com [Source type: Reference]

.If one variable is already known, a receiver can determine its position using only three satellites.^ Aiding location determinations in satellite positioning system receivers .
  • Combining GPS with TOA/TDOA of ... - Google Patent Search 27 January 2010 23:56 UTC www.google.com [Source type: Reference]

^ From the distance to three satellites, the receiver can triangulate or fix its position accurately.
  • Space Today Online - Satellites - NAVSTAR global positioning system GPS satellites 22 September 2009 23:43 UTC www.spacetoday.org [Source type: FILTERED WITH BAYES]

^ By determining the position of, and distance to, at least three satellites, the receiver can compute its position using trilateration.
  • Global Positioning System! 27 January 2010 23:56 UTC www.kipaddotta.com [Source type: FILTERED WITH BAYES]

.(For example, a ship or plane may have known elevation.^ If one variable is already known (for example, a sea-going ship knows its altitude is 0), a receiver can determine its position using only three satellites.
  • Global Positioning System (GPS) - History, Facts and Pictures 27 January 2010 23:56 UTC www.aviationexplorer.com [Source type: Reference]

^ For example if the position of receiver 1 is known but the position of receiver 2 unknown, it may be possible to estimate the position of receiver 2 using numerical root finding and least squares .
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ If one variable is already known (for example, a ship or plane may have known elevation), a receiver can determine its position using only three satellites.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

) .Some GPS receivers may use additional clues or assumptions (such as reusing the last known altitude, dead reckoning, inertial navigation, or including information from the vehicle computer) to give a degraded position when fewer than four satellites are visible (see,[21] Chapters 7 and 8 of,[22] and [23]).^ The receiver's computer then uses trigonometry to find its own position from the known points in the sky.
  • Space Today Online - Satellites - NAVSTAR global positioning system GPS satellites 22 September 2009 23:43 UTC www.spacetoday.org [Source type: FILTERED WITH BAYES]

^ Four satellites (normal navigation) can be used to determine three position dimensions and time.
  • Unit 017 - Global Positioning System Overview 27 January 2010 23:56 UTC www.ncgia.ucsb.edu [Source type: Reference]

^ This information is used for navigation, positioning, time dissemination, and research.
  • Precision Farming Tools: Global Positioning System (GPS) - Virginia Cooperative Extension 27 January 2010 23:56 UTC www.ext.vt.edu [Source type: Reference]

Position calculation introduction

.To provide an introductory description of how a GPS receiver works, errors will be ignored in this section.^ To provide an introductory description of how a GPS receiver works, measurement errors will be ignored in this section.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ To describe the basic concept of how a GPS receiver works, the errors are at first ignored.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ How the GPS works.
  • A Practical Guide to GPS -UTM 13 January 2010 11:56 UTC www.dbartlett.com [Source type: FILTERED WITH BAYES]

.Using messages received from a minimum of four visible satellites, a GPS receiver is able to determine the times sent and then the satellite positions corresponding to these times sent.^ Four satellites (normal navigation) can be used to determine three position dimensions and time.
  • Unit 017 - Global Positioning System Overview 27 January 2010 23:56 UTC www.ncgia.ucsb.edu [Source type: Reference]

^ In space, satellites and spacecraft rely on GPS to determine their position and orientation.
  • GLOBAL POSITIONING SYSTEM (GPS), 27 January 2010 23:56 UTC www.history.com [Source type: FILTERED WITH BAYES]

^ Time, position and fix related data for a GPS receiver.
  • Glenn Baddeley - GPS - NMEA sentence information 13 January 2010 11:56 UTC home.mira.net [Source type: Reference]

.The x, y, and z components of position, and the time sent, are designated as \scriptstyle\left[x_i,\, y_i,\, z_i,\, t_i\right] where the subscript i is the satellite number and has the value 1, 2, 3, or 4. Knowing the indicated time the message was received \scriptstyle\ tr, the GPS receiver can compute the transit time of the message as \scriptstyle\left (tr-t_i\right ) .^ Let and denote the true coordinates of GPS receiver position at time, .
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ Knowing the indicated time the message was received , the GPS receiver can compute the indicated transit time, .
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ Then the final accurate position is derived from data received from a number of satellites.

.Assuming the message traveled at the speed of light, c, the distance traveled, \scriptstyle p_i can be computed as \scriptstyle\left (tr-t_i\right )c.^ Assuming the message traveled at the speed of light, c , the distance traveled, can be computed as .
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ Assume the message travels at the speed of light , then the pseudorange satisfies the equation, .
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ Measuring the time delay between transmission and reception of each GPS radio signal gives the distance to each satellite, since the signal travels at a known speed.

.A satellite's position and distance from the receiver define a spherical surface, centered on the satellite.^ Knowing the distance from GPS receiver to a satellite and the position of a satellite implies that the GPS receiver is on the surface of a sphere centered at the position of a satellite.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ Multipath is caused by reflected signals from surfaces near the receiver that can either interfere with or be mistaken for the signal that follows the straight line path from the satellite.
  • Unit 017 - Global Positioning System Overview 27 January 2010 23:56 UTC www.ncgia.ucsb.edu [Source type: Reference]

^ Knowing the position and the distance of a satellite indicates that the receiver is located somewhere on the surface of an imaginary sphere centered on that satellite and whose radius is the distance to it.
  • Global Positioning System! 27 January 2010 23:56 UTC www.kipaddotta.com [Source type: FILTERED WITH BAYES]
  • Global Positioning System (GPS) - History, Facts and Pictures 27 January 2010 23:56 UTC www.aviationexplorer.com [Source type: Reference]

.The position of the receiver is somewhere on this surface.^ Knowing the position and the distance of a satellite indicates that the receiver is located somewhere on the surface of an imaginary sphere centered on that satellite and whose radius is the distance to it.
  • Global Positioning System! 27 January 2010 23:56 UTC www.kipaddotta.com [Source type: FILTERED WITH BAYES]
  • Global Positioning System (GPS) - History, Facts and Pictures 27 January 2010 23:56 UTC www.aviationexplorer.com [Source type: Reference]

^ Thus we know that the indicated position of the GPS receiver is at or near the intersection of the surfaces of four spheres.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ The correct position of the GPS receiver is also the intersection which is closest to the surface of the sphere corresponding to the fourth satellite.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

.Thus with four satellites, the indicated position of the GPS receiver is at or near the intersection of the surfaces of four spheres.^ Thus we know that the indicated position of the GPS receiver is at or near the intersection of the surfaces of four spheres.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ Using messages received from four satellites, the GPS receiver is able to determine the satellite positions and time sent.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ A typical GPS receiver calculates its position using the signals from four or more GPS satellites.
  • Global Positioning System (GPS) - History, Facts and Pictures 27 January 2010 23:56 UTC www.aviationexplorer.com [Source type: Reference]

.(In the ideal case of no errors, the GPS receiver would be at a precise intersection of the four surfaces.^ In the ideal case of no errors, the GPS receiver will be at an intersection of the surfaces of four spheres.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ Signal multi path This occurs when the GPS signal is reflected off objects such as tall buildings or large rock surfaces before it reaches the receiver.
  • How does the Global Positioning System (GPS) work ? 27 January 2010 23:56 UTC www.pocketgpsworld.com [Source type: General]

^ We assumed a Gaussian error distribution for measurements of latitude and longitude, which has been shown to be reasonably representative of coordinate measurements based on stand-alone GPS receivers [ 66 ].
  • International Journal of Health Geographics | Full text | Development of a wearable global positioning system for place and health research 27 January 2010 23:56 UTC www.ij-healthgeographics.com [Source type: Academic]

)
.If the surfaces of two spheres intersect at more than one point, they intersect in a circle.^ Two sphere surfaces intersecting in a circle The article, trilateration , shows mathematically that two spheres intersecting in more than one point intersect in a circle.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ The distance between these two points is the diameter of the circle of intersection.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ The two circles should intersect at two points - one of which should be your real position.
  • TidBITS#388/14-Jul-97 9 October 2009 7:11 UTC www.tidbits.com [Source type: FILTERED WITH BAYES]

.The article trilateration shows this mathematically.^ Again trilateration clearly shows this mathematically.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ Two sphere surfaces intersecting in a circle The article, trilateration , shows mathematically that two spheres intersecting in more than one point intersect in a circle.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ Two sphere surfaces intersecting in a circle The article, trilateration , shows mathematically how the equation for a circle is determined.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

.A figure, Two Sphere Surfaces Intersecting in a Circle, is shown below.^ The intersection of two spheres is a circle ; so the receiver must be located somewhere on that circle.
  • Global Positioning System@Everything2.com 27 January 2010 23:56 UTC www.everything2.com [Source type: FILTERED WITH BAYES]

^ The two circles should intersect at two points - one of which should be your real position.
  • TidBITS#388/14-Jul-97 9 October 2009 7:11 UTC www.tidbits.com [Source type: FILTERED WITH BAYES]

^ You are at either of the two points where the two arcs or circles intersect, but which one?
  • A Practical Guide to GPS -UTM 13 January 2010 11:56 UTC www.dbartlett.com [Source type: FILTERED WITH BAYES]

Two sphere surfaces intersecting in a circle
.The intersection of a third spherical surface with the first two will be its intersection with that circle; in most cases of practical interest, this means they intersect at two points.^ The distance between these two points is the diameter of the circle of intersection.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ A circle and sphere surface in most cases of practical interest intersect at two points, although it is conceivable that they could intersect in 0 or 1 point.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ Surface of a sphere intersecting a circle (i.e., the edge of a disk) at two points A circle and sphere surface in most cases of practical interest intersect at two points, although it is conceivable that they could intersect at one point—or not at all.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

[24] .Another figure, Surface of Sphere Intersecting a Circle (not disk) at Two Points, illustrates the intersection.^ The distance between these two points is the diameter of the circle of intersection.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ It is clearly shown in trilateration that the surfaces of three spheres intersect in 0, 1, or 2 points.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ The surfaces of two spheres, if they intersect in more than one point, intersect in a circle.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

.The two intersections are marked with dots.^ The two intersections are marked with dots.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ Two points at which the surfaces of the spheres intersect are clearly marked on the figure.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

.Again the article trilateration clearly shows this mathematically.^ Again trilateration clearly shows this mathematically.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ Two sphere surfaces intersecting in a circle The article, trilateration , shows mathematically that two spheres intersecting in more than one point intersect in a circle.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ Two sphere surfaces intersecting in a circle The article, trilateration , shows mathematically how the equation for a circle is determined.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

Surface of sphere Intersecting a circle (not disk) at two points
.For automobiles and other near-earth-vehicles, the correct position of the GPS receiver is the intersection closest to the Earth's surface.^ The near-Earth intersection will be the correct position for the case of a near-Earth vehicle.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ Thus we know that the indicated position of the GPS receiver is at or near the intersection of the surfaces of four spheres.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ The correct position of the GPS receiver is the one that is closest to the fourth sphere.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

.For space vehicles, the intersection farthest from Earth may be the correct one.^ The near-Earth intersection will be the correct position for the case of a near-Earth vehicle.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ The intersection which is farthest from Earth may be the correct position for space vehicles.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ Based on the intersection of a group of satellites' signals, triangulation or satellite ranging is used to calculate a location on earth by measuring the distance from each of several satellites in space.
  • Precision Farming Tools: Global Positioning System (GPS) - Virginia Cooperative Extension 27 January 2010 23:56 UTC www.ext.vt.edu [Source type: Reference]

[25]
.The correct position for the GPS receiver is also the intersection closest to the surface of the sphere corresponding to the fourth satellite.^ Thus we know that the indicated position of the GPS receiver is at or near the intersection of the surfaces of four spheres.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ The correct position of the GPS receiver is the one that is closest to the fourth sphere.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ The correct position of the GPS receiver is also the intersection which is closest to the surface of the sphere corresponding to the fourth satellite.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

Correcting a GPS receiver's clock

.The method of calculating position for the case of no errors has been explained.^ The method of calculating position for the case of no errors has been explained.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ Buildings, terrain, electronic interference, or sometimes even dense foliage can block signal reception, causing position errors or possibly no position reading at all.
  • How does the Global Positioning System (GPS) work ? 27 January 2010 23:56 UTC www.pocketgpsworld.com [Source type: General]

^ A method for correcting GPS measurements by comparing bias errors between a known location and the position of a "roving" GPS receiver.
  • Unit 017 - Global Positioning System Overview 27 January 2010 23:56 UTC www.ncgia.ucsb.edu [Source type: Reference]

.One of the most significant error sources is the GPS receiver's clock.^ GPS Accuracy and error sources .
  • Global Positioning System! 27 January 2010 23:56 UTC www.kipaddotta.com [Source type: FILTERED WITH BAYES]

^ GPS Ephemeris and clock errors .
  • Global Positioning System! 27 January 2010 23:56 UTC www.kipaddotta.com [Source type: FILTERED WITH BAYES]

^ Correcting a GPS receiver's clock .
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

.Because of the very large value of the speed of light, c, the estimated distances from the GPS receiver to the satellites, the pseudoranges, are very sensitive to errors in the GPS receiver clock.^ Because of the very large value of the speed of light , c , the estimated distances from the GPS receiver to the satellites, the pseudoranges, are very sensitive to errors in the GPS receiver clock.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ Both GPS satellites and receivers are prone to timing errors.
  • Chemistry - Global Positioning System 27 January 2010 23:56 UTC www.chemistrydaily.com [Source type: Reference]

^ Receiver clock errors A receiver's built-in clock is not as accurate as the atomic clocks onboard the GPS satellites.
  • How does the Global Positioning System (GPS) work ? 27 January 2010 23:56 UTC www.pocketgpsworld.com [Source type: General]

.This suggests that an extremely accurate and expensive clock is required for the GPS receiver to work.^ This suggests that an extremely accurate and expensive clock is required for the GPS receiver to work.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ Correcting a GPS receiver's clock .
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ The Navstar GPS constellation worked in concert with ground receivers to give precise location information to military and civilian users anywhere in the world.
  • GPS Block 2 and 2A 27 January 2010 23:56 UTC www.astronautix.com [Source type: FILTERED WITH BAYES]

.On the other hand, manufacturers prefer to build inexpensive GPS receivers for mass markets.^ On the other hand, manufacturers prefer to build inexpensive GPS receivers for mass markets.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ By contrast, consumer GPS receivers, originally developed for recreational uses (such as fishing, hiking, and auto trips) are much more affordable because they are mass-produced for a wider market.
  • Precision Farming Tools: Global Positioning System (GPS) - Virginia Cooperative Extension 27 January 2010 23:56 UTC www.ext.vt.edu [Source type: Reference]

^ Signal multi path This occurs when the GPS signal is reflected off objects such as tall buildings or large rock surfaces before it reaches the receiver.
  • How does the Global Positioning System (GPS) work ? 27 January 2010 23:56 UTC www.pocketgpsworld.com [Source type: General]

.The solution for this dilemma is based on the way sphere surfaces intersect in the GPS problem.^ The solution for this dilemma is based on the way sphere surfaces intersect in the GPS problem.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ Two sphere surfaces intersecting in a circle The article, trilateration , shows mathematically that two spheres intersecting in more than one point intersect in a circle.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ It is likely the surfaces of the three spheres intersect since the circle of intersection of the first two spheres is normally quite large and thus the third sphere surface is likely to intersect this large circle.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

Diagram depicting satellite 4, sphere, p4, r4, and da
.It is likely that the surfaces of the three spheres intersect, since the circle of intersection of the first two spheres is normally quite large, and thus the third sphere surface is likely to intersect this large circle.^ It is likely the surfaces of the three spheres intersect since the circle of intersection of the first two spheres is normally quite large and thus the third sphere surface is likely to intersect this large circle.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ It is clearly shown in trilateration that the surfaces of three spheres intersect in 0, 1, or 2 points.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ The surfaces of two spheres, if they intersect in more than one point, intersect in a circle.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

.It is very unlikely that the surface of the sphere corresponding to the fourth satellite will intersect either of the two points of intersection of the first three, since any clock error could cause it to miss intersecting a point.^ It is very unlikely that the surface of the sphere corresponding to the fourth satellite will intersect either of the two points of intersection of the first three since any clock error could cause it to miss intersecting a point.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ It is likely the surfaces of the three spheres intersect since the circle of intersection of the first two spheres is normally quite large and thus the third sphere surface is likely to intersect this large circle.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ It is clearly shown in trilateration that the surfaces of three spheres intersect in 0, 1, or 2 points.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

.However, the distance from the valid estimate of GPS receiver position to the surface of the sphere corresponding to the fourth satellite can be used to compute a clock correction.^ GPS receiver clock can be advanced if is positive or delayed if is negative.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ Using messages received from four satellites, the GPS receiver is able to determine the satellite positions and time sent.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ The correct position of the GPS receiver is the one that is closest to the fourth sphere.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

.Let \scriptstyle r_4 denote the distance from the valid estimate of GPS receiver position to the fourth satellite and let \scriptstyle p_4 denote the pseudorange of the fourth satellite.^ Let and denote the true coordinates of GPS receiver position at time, .
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ Let denote the phase of the carrier of satellite j measured by receiver i at time .
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ The correct position of the GPS receiver is the one that is closest to the fourth sphere.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

Let \scriptstyle da \,=\, r_4 \,-\, p_4. .Note that \scriptstyle da is the distance from the computed GPS receiver position to the surface of the sphere corresponding to the fourth satellite.^ The correct position of the GPS receiver is the one that is closest to the fourth sphere.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ The correct position of the GPS receiver is also the intersection which is closest to the surface of the sphere corresponding to the fourth satellite.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ The receiver measures the transit time of each message and computes the distance to each satellite.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

Thus the quotient, \scriptstyle b \,=\, da / c\ , provides an estimate of
(correct time) − (time indicated by the receiver's on-board clock),
and the .GPS receiver clock can be advanced if \scriptstyle b is positive or delayed if \scriptstyle b is negative.^ GPS receiver clock can be advanced if is positive or delayed if is negative.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ Correcting a GPS receiver's clock .
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ The GPS receiver's reported position coordinates.
  • Micro Modular Technologies - GPS and Wireless Modules - Support 27 January 2010 23:56 UTC www.micro-modular.com [Source type: Reference]

System segmentation

Unlaunched GPS satellite on display at the San Diego Aerospace museum
.The current GPS consists of three major segments.^ The current GPS consists of three major segments..
  • Global Positioning System! 27 January 2010 23:56 UTC www.kipaddotta.com [Source type: FILTERED WITH BAYES]

^ The current GPS consists of three major segments.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ A GPS system consists of a space segment (up to 24 NAVSTAR satellites in six different orbits); The control segment with five monitor stations, one master control station and three upload stations.
  • GPS Basic Information for Educators 13 January 2010 11:56 UTC www.gps4educators.com [Source type: Reference]

.These are the space segment (SS), a control segment (CS), and a user segment (US).^ Components of a GPS The GPS is divided into three major components The Control Segment The Space Segments The User Segment The Control Segment The Control Segment consists of five monitoring stations (Colorado Springs, Ascesion Island, Diego Garcia, Hawaii, and Kwajalein Island).
  • GIS Tutorials: Global Positioning System 27 January 2010 23:56 UTC www.gisdevelopment.net [Source type: FILTERED WITH BAYES]

^ Global Positioning System (GPS) - The system of user, space, and control segments providing position, velocity, and time service which is operated by the US Department of Defense Its full name is NAVSTAR GPS .
  • Micro Modular Technologies - GPS and Wireless Modules - Support 27 January 2010 23:56 UTC www.micro-modular.com [Source type: Reference]

^ The space segment (SS) is composed of the orbiting GPS satellites, or Space Vehicles (SV) in GPS parlance.
  • Global Positioning System! 27 January 2010 23:56 UTC www.kipaddotta.com [Source type: FILTERED WITH BAYES]

[26]

Space segment

.See also section 4.3 of "Essentials of Satellite Navigation Compendium", GPS satellite, List of GPS satellite launches, and Chapter 6 of The global positioning system by Parkinson and Spilker.^ Global Positioning System (GPS) is a navigational aid originally urbanized for the military.
  • Global Positioning System - GPS Systems & GPS System 27 January 2010 23:56 UTC www.streetdirectory.com [Source type: General]

^ The Global Positioning System (GPS) is a satellite navigation system.
  • Global Positioning System - GPS Systems & GPS System 27 January 2010 23:56 UTC www.streetdirectory.com [Source type: General]

^ An overview of the global positioning system (GPS).
  • Precision Farming Tools: Global Positioning System (GPS) - Virginia Cooperative Extension 27 January 2010 23:56 UTC www.ext.vt.edu [Source type: Reference]

.
A visual example of the GPS constellation in motion with the Earth rotating.
^ See also: GPS satellite and List of GPS satellite launches A visual example of the GPS constellation in motion with the Earth rotating.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ The satellites which supply the navigation message and precise time , the basis of the GPS concept, are located 11,000 nautical mile s above the earth in a widely dispersed constellation.
  • Global Positioning System@Everything2.com 27 January 2010 23:56 UTC www.everything2.com [Source type: FILTERED WITH BAYES]

^ It is based on Global Positioning System or GPS. It is a constellation of satellites that orbit the earth twice a day, time and the transmission of positioning data.

Notice how the number of satellites in view from a given point on the Earth's surface, in this example at 45°N, changes with time.
.The space segment (SS) is composed of the orbiting GPS satellites, or Space Vehicles (SV) in GPS parlance.^ Constellation- The set of GPS satellites in orbit.
  • Micro Modular Technologies - GPS and Wireless Modules - Support 27 January 2010 23:56 UTC www.micro-modular.com [Source type: Reference]

^ Artist's conception of GPS satellite in orbit .
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ The Space Segment of the system consists of the 24 GPS satellites.
  • Unit 017 - Global Positioning System Overview 27 January 2010 23:56 UTC www.ncgia.ucsb.edu [Source type: Reference]

.The GPS design originally called for 24 SVs, eight each in three circular orbital planes,[27] but this was modified to six planes with four satellites each.^ The GPS design originally called for 24 SVs, eight each in three circular orbital planes, but this was modified to six planes with four satellites each.
  • Global Positioning System (GPS) - History, Facts and Pictures 27 January 2010 23:56 UTC www.aviationexplorer.com [Source type: Reference]

^ The GPS design calls for 24 SVs to be distributed equally among six circular orbital planes.
  • Global Positioning System! 27 January 2010 23:56 UTC www.kipaddotta.com [Source type: FILTERED WITH BAYES]

^ There are four satellites in each of six orbital planes.
  • GPS GLOBAL POSITIONING SYSTEM 27 January 2010 23:56 UTC www.speedace.info [Source type: FILTERED WITH BAYES]

[28] .The orbital planes are centered on the Earth, not rotating with respect to the distant stars.^ The orbital planes are centered on the Earth, not rotating with respect to the distant stars.
  • Global Positioning System! 27 January 2010 23:56 UTC www.kipaddotta.com [Source type: FILTERED WITH BAYES]
  • Global Positioning System (GPS) - History, Facts and Pictures 27 January 2010 23:56 UTC www.aviationexplorer.com [Source type: Reference]
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ There currently are 24 operational satellites as part of the GPS satellite constellation, that orbit the earth with a orbital radius of ~16,000 miles (from the center of the earth).
  • Global Positioning System - GPS Systems & GPS System 27 January 2010 23:56 UTC www.streetdirectory.com [Source type: General]

^ The GPS time scale is defined in an inertial system but observations are processed in an Earth-centered, Earth-fixed (co-rotating) system, a system in which simultaneity is not uniquely defined.
  • Global Positioning System! 27 January 2010 23:56 UTC www.kipaddotta.com [Source type: FILTERED WITH BAYES]
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

[29] .The six planes have approximately 55° inclination (tilt relative to Earth's equator) and are separated by 60° right ascension of the ascending node (angle along the equator from a reference point to the orbit's intersection).^ The six planes have approximately 55° inclination (tilt relative to Earth's equator) and are separated by 60° right ascension of the ascending node (angle along the equator from a reference point to the orbit's intersection).
  • Global Positioning System! 27 January 2010 23:56 UTC www.kipaddotta.com [Source type: FILTERED WITH BAYES]
  • Global Positioning System (GPS) - History, Facts and Pictures 27 January 2010 23:56 UTC www.aviationexplorer.com [Source type: Reference]

^ The six planes have approximately 55° inclination (tilt relative to Earth's equator ) and are separated by 60° right ascension of the ascending node (angle along the equator from a reference point to the orbit's intersection).The orbits are arranged so that at least six satellites are always within line of sight from almost everywhere on Earth's surface.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ Inclination : 55.60 deg.
  • GPS Block 2 and 2A 27 January 2010 23:56 UTC www.astronautix.com [Source type: FILTERED WITH BAYES]

[30] .The orbits are arranged so that at least six satellites are always within line of sight from almost everywhere on Earth's surface.^ The orbits are arranged so that at least six satellites are always within line of sight from almost everywhere on Earth's surface.
  • Global Positioning System! 27 January 2010 23:56 UTC www.kipaddotta.com [Source type: FILTERED WITH BAYES]
  • Global Positioning System (GPS) - History, Facts and Pictures 27 January 2010 23:56 UTC www.aviationexplorer.com [Source type: Reference]

^ The orbits are designed so at least four satellites are always within line of sight from almost any place on earth.
  • GPS GLOBAL POSITIONING SYSTEM 27 January 2010 23:56 UTC www.speedace.info [Source type: FILTERED WITH BAYES]

^ The six planes have approximately 55° inclination (tilt relative to Earth's equator ) and are separated by 60° right ascension of the ascending node (angle along the equator from a reference point to the orbit's intersection).The orbits are arranged so that at least six satellites are always within line of sight from almost everywhere on Earth's surface.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

[31]
.Orbiting at an altitude of approximately 20,200 kilometers (about 12,550 miles or 10,900 nautical miles; orbital radius of approximately 26,600 km (about 16,500 mi or 14,400 NM)), each SV makes two complete orbits each sidereal day, repeating the same ground track each day.^ Each satellite circles the Earth twice every day at an altitude of 20,200 kilometres (12,600 miles).
  • Chemistry - Global Positioning System 27 January 2010 23:56 UTC www.chemistrydaily.com [Source type: Reference]

^ The ground track of each satellite therefore repeats each (sidereal) day.
  • Global Positioning System (GPS) - History, Facts and Pictures 27 January 2010 23:56 UTC www.aviationexplorer.com [Source type: Reference]

^ The orbital radius was 26,562 km, corresponding to a period of revolution of 12 sidereal hours, with repeating ground traces.
  • The Global Positioning System: a detailed lookedat the miracle of modern navigation; by Robert A. Nelson 27 January 2010 23:56 UTC www.aticourses.com [Source type: FILTERED WITH BAYES]

[32] .This was very helpful during development, since even with just four satellites, correct alignment means all four are visible from one spot for a few hours each day.^ This was very helpful during development, since even with just four satellites, correct alignment means all four are visible from one spot for a few hours each day.
  • Global Positioning System (GPS) - History, Facts and Pictures 27 January 2010 23:56 UTC www.aviationexplorer.com [Source type: Reference]
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ The receiver contains a mathematical model to account for these influences, and the satellites also broadcast some related information which helps the receiver in estimating the correct speed of propagation.
  • Chemistry - Global Positioning System 27 January 2010 23:56 UTC www.chemistrydaily.com [Source type: Reference]

^ Users with a GPS unit can determine their exact location (latitude and longitude) in any weather condition, all over the world, 24 hours a day.
  • Alaska Hunter Safety Course - Global Positioning System 27 January 2010 23:56 UTC www.hunter-ed.com [Source type: General]

.For military operations, the ground track repeat can be used to ensure good coverage in combat zones.^ For military operations, the ground track repeat can be used to ensure good coverage in combat zones.
  • Global Positioning System (GPS) - History, Facts and Pictures 27 January 2010 23:56 UTC www.aviationexplorer.com [Source type: Reference]
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ The ground track of each satellite therefore repeats each (sidereal) day.
  • Global Positioning System (GPS) - History, Facts and Pictures 27 January 2010 23:56 UTC www.aviationexplorer.com [Source type: Reference]

^ Use of GPS receivers revolutionized civilian and military operations of every kind by providing precise location information.
  • GPS Block 2 and 2A 27 January 2010 23:56 UTC www.astronautix.com [Source type: FILTERED WITH BAYES]

.As of March 2008,[33] there are 31 actively broadcasting satellites in the GPS constellation, and two older, retired from active service satellites kept in the constellation as orbital spares.^ Constellation- The set of GPS satellites in orbit.
  • Micro Modular Technologies - GPS and Wireless Modules - Support 27 January 2010 23:56 UTC www.micro-modular.com [Source type: Reference]

^ As of September 2007, there are 31 actively broadcasting satellites in the GPS constellation.
  • Global Positioning System! 27 January 2010 23:56 UTC www.kipaddotta.com [Source type: FILTERED WITH BAYES]
  • Global Positioning System (GPS) - History, Facts and Pictures 27 January 2010 23:56 UTC www.aviationexplorer.com [Source type: Reference]

^ GPS satellites broadcast on two links to users: L1 and L2.

.The additional satellites improve the precision of GPS receiver calculations by providing redundant measurements.^ Satellite maneuvers are not precise by GPS standards.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ A measure of the quality of satellite geometry as seen by the GPS receiver.
  • Micro Modular Technologies - GPS and Wireless Modules - Support 27 January 2010 23:56 UTC www.micro-modular.com [Source type: Reference]

^ The additional satellites improve the precision of GPS receiver calculations by providing redundant measurements.
  • Global Positioning System! 27 January 2010 23:56 UTC www.kipaddotta.com [Source type: FILTERED WITH BAYES]
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

.With the increased number of satellites, the constellation was changed to a nonuniform arrangement.^ Satellite constellation - The arrangement in space of a set of satellites.
  • Precision Farming Tools: Global Positioning System (GPS) - Virginia Cooperative Extension 27 January 2010 23:56 UTC www.ext.vt.edu [Source type: Reference]

^ With the increased number of satellites, the constellation was changed to a nonuniform arrangement.
  • Global Positioning System! 27 January 2010 23:56 UTC www.kipaddotta.com [Source type: FILTERED WITH BAYES]
  • Global Positioning System (GPS) - History, Facts and Pictures 27 January 2010 23:56 UTC www.aviationexplorer.com [Source type: Reference]
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ Satellite constellation The arrangement in space of a set of satellites.
  • WQ452 Precision Agriculture: Global Positioning System | University of Missouri Extension 27 January 2010 23:56 UTC extension.missouri.edu [Source type: Reference]

.Such an arrangement was shown to improve reliability and availability of the system, relative to a uniform system, when multiple satellites fail.^ Such an arrangement was shown to improve reliability and availability of the system, relative to a uniform system, when multiple satellites fail.
  • Global Positioning System! 27 January 2010 23:56 UTC www.kipaddotta.com [Source type: FILTERED WITH BAYES]
  • Global Positioning System (GPS) - History, Facts and Pictures 27 January 2010 23:56 UTC www.aviationexplorer.com [Source type: Reference]
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ Such an antenna improves the signal-to-noise ratio of a GPS system, and it boosts the weak signals a receiver must process.
  • Exploring GPS - 2003-09-22 00:00:00 | Design News 16 January 2010 16:26 UTC www.designnews.com [Source type: FILTERED WITH BAYES]

^ The atomic clocks on board the GPS satellites are precisely tuned, making the system a practical engineering application of the scientific theory of relativity in a real-world environment.
  • Global Positioning System! 27 January 2010 23:56 UTC www.kipaddotta.com [Source type: FILTERED WITH BAYES]

[34] .About eight satellites are visible from any point on the ground at any one time (see animation at right).^ SV clocks are monitored by ground control stations and occasionally reset to maintain time to within one millisecond of GPS time.
  • Unit 017 - Global Positioning System Overview 27 January 2010 23:56 UTC www.ncgia.ucsb.edu [Source type: Reference]

^ It uses the precise time to produce an identical random seed to the one the satellite is using.
  • Global Positioning System@Everything2.com 27 January 2010 23:56 UTC www.everything2.com [Source type: FILTERED WITH BAYES]

^ Low-cost receivers receive signals from one satellite at a time and require more time to determine the location than a receiver capable of receiving four signals simultaneously.
  • WQ452 Precision Agriculture: Global Positioning System | University of Missouri Extension 27 January 2010 23:56 UTC extension.missouri.edu [Source type: Reference]

Control segment

The Control Segment is composed of
  1. a Master Control Station (MCS),
  2. an Alternate Master Control Station,
  3. four dedicated Ground Antennas and
  4. six dedicated Monitor Stations.
.The MCS can also access U.S. Air Force Satellite Control Network (AFSCN) ground antennas (for additional command and control capability) and NGA (National Geospatial-Intelligence Agency) monitor stations.^ The ground control segment consists of five monitoring stations, three ground antennas, and a master control station.
  • International Journal of Health Geographics | Full text | Development of a wearable global positioning system for place and health research 27 January 2010 23:56 UTC www.ij-healthgeographics.com [Source type: Academic]

^ The GPS worldwide satellite network consists of six monitor stations and four ground antenna stations.

^ Bradford Parkinson, professor of aeronautics and astronautics at Stanford University, conceived the present satellite-based system in the early 1960s and developed it in conjunction with the U.S. Air Force.
  • Global Positioning System! 27 January 2010 23:56 UTC www.kipaddotta.com [Source type: FILTERED WITH BAYES]

.The flight paths of the satellites are tracked by dedicated U.S. Air Force monitoring stations in Hawaii, Kwajalein, Ascension Island, Diego Garcia, Colorado Springs, Colorado and Cape Canaveral, along with shared NGA monitor stations operated in England, Argentina, Ecuador, Bahrain, Australia and Washington DC. [35] The tracking information is sent to the Air Force Space Command's MCS at Schriever Air Force Base 16 miles ESE of Colorado Springs, which is operated by the 2nd Space Operations Squadron (2 SOPS) of the United States Air Force (USAF).^ The satellite constellation is managed by the United States Air Force 50th Space Wing.
  • Global Positioning System! 27 January 2010 23:56 UTC www.kipaddotta.com [Source type: FILTERED WITH BAYES]
  • Global Positioning System (GPS) - History, Facts and Pictures 27 January 2010 23:56 UTC www.aviationexplorer.com [Source type: Reference]

^ The monitoring stations passively track all satellites in view and accumulate ranging information.
  • International Journal of Health Geographics | Full text | Development of a wearable global positioning system for place and health research 27 January 2010 23:56 UTC www.ij-healthgeographics.com [Source type: Academic]

^ Data from the monitor stations is continually sent to the GPS Master Control Station (MCS), located at Schriever Air Force Base, Colorado, for processing.

.Then 2 SOPS contacts each GPS satellite regularly with a navigational update using dedicated or shared (AFSCN) ground antennas (GPS dedicated ground antennas are located at Kwajalein, Ascension Island, Diego Garcia, and Cape Canaveral).^ GPS receivers use triangulation of the GPS satellites' navigational signals to determine their location.
  • Global Positioning System (GPS) Program 27 January 2010 23:56 UTC leonardo.jpl.nasa.gov [Source type: Reference]
  • Global Positioning System (GPS) Program 13 January 2010 11:56 UTC samadhi.jpl.nasa.gov [Source type: Reference]

^ The monitor stations (located at Ascension Island, Cape Canaveral, Colorado Springs, Diego Garcia, Kwajalein and Hawaii) use specially-designed GPS receivers to passively track the navigation signals of all of the satellites.

^ Navigation Technical Satellite; GPS precursor.

.These updates synchronize the atomic clocks on board the satellites to within a few nanoseconds of each other, and adjust the ephemeris of each satellite's internal orbital model.^ The updates synchronize the atomic clocks onboard each satellite to within one microsecond, and also adjust the ephemeris of the satellites' internal orbital model to match the observations of the satellites from the ground.
  • GPS GLOBAL POSITIONING SYSTEM 27 January 2010 23:56 UTC www.speedace.info [Source type: FILTERED WITH BAYES]

^ These updates synchronize the atomic clocks on board the satellites to within one microsecond and adjust the ephemeris of each satellite's internal orbital model.
  • Global Positioning System! 27 January 2010 23:56 UTC www.kipaddotta.com [Source type: FILTERED WITH BAYES]

^ This is an enormous rate difference for an atomic clock with a precision of a few nanoseconds.
  • The Global Positioning System: a detailed lookedat the miracle of modern navigation; by Robert A. Nelson 27 January 2010 23:56 UTC www.aticourses.com [Source type: FILTERED WITH BAYES]

.The updates are created by a Kalman filter which uses inputs from the ground monitoring stations, space weather information, and various other inputs.^ The updates are created by a Kalman filter which uses inputs from the ground monitoring stations, space weather information, and various other inputs.
  • Global Positioning System! 27 January 2010 23:56 UTC www.kipaddotta.com [Source type: FILTERED WITH BAYES]
  • Global Positioning System (GPS) - History, Facts and Pictures 27 January 2010 23:56 UTC www.aviationexplorer.com [Source type: Reference]
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ Before its civilian applications, GPS was used to provide all-weather round-the-clock navigation capabilities for military ground, sea, and air forces.

^ SV clocks are monitored by ground control stations and occasionally reset to maintain time to within one millisecond of GPS time.
  • Unit 017 - Global Positioning System Overview 27 January 2010 23:56 UTC www.ncgia.ucsb.edu [Source type: Reference]

[36]
.Satellite maneuvers are not precise by GPS standards.^ Satellite maneuvers are not precise by GPS standards.
  • Global Positioning System (GPS) - History, Facts and Pictures 27 January 2010 23:56 UTC www.aviationexplorer.com [Source type: Reference]
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ The satellites which supply the navigation message and precise time , the basis of the GPS concept, are located 11,000 nautical mile s above the earth in a widely dispersed constellation.
  • Global Positioning System@Everything2.com 27 January 2010 23:56 UTC www.everything2.com [Source type: FILTERED WITH BAYES]

^ The atomic clocks on board the GPS satellites are precisely tuned, making the system a practical engineering application of the scientific theory of relativity in a real-world environment.
  • Global Positioning System! 27 January 2010 23:56 UTC www.kipaddotta.com [Source type: FILTERED WITH BAYES]

.So to change the orbit of a satellite, the satellite must be marked unhealthy, so receivers will not use it in their calculation.^ So to change the orbit of a satellite, the satellite must be marked 'unhealthy', so receivers will not use it in their calculation.
  • Global Positioning System (GPS) - History, Facts and Pictures 27 January 2010 23:56 UTC www.aviationexplorer.com [Source type: Reference]
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ The rate of change between the satellite and receiver.
  • NPS GPS Support Facility - Glossary of Common GPS Terms 13 January 2010 11:56 UTC www.nps.gov [Source type: Reference]

^ With each guess, a geometric dilution of precision (GDOP) vector is calculated, based on the relative sky positions of the satellites used.
  • Global Positioning System! 27 January 2010 23:56 UTC www.kipaddotta.com [Source type: FILTERED WITH BAYES]

.Then the maneuver can be carried out, and the resulting orbit tracked from the ground.^ Then the maneuver can be carried out, and the resulting orbit tracked from the ground.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ Carrier-phase tracking of GPS signals has resulted in a revolution in land surveying.
  • Unit 017 - Global Positioning System Overview 27 January 2010 23:56 UTC www.ncgia.ucsb.edu [Source type: Reference]

.Then the new ephemeris is uploaded and the satellite marked healthy again.^ Then the new ephemeris is uploaded and the satellite marked healthy again.
  • Global Positioning System (GPS) - History, Facts and Pictures 27 January 2010 23:56 UTC www.aviationexplorer.com [Source type: Reference]
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

User segment

GPS receivers come in a variety of formats, from devices integrated into cars, phones, and watches, to dedicated devices such as those shown here from manufacturers Trimble, Garmin and Leica (left to right).
.The User Segment is composed of hundreds of thousands of U.S. and allied military users of the secure GPS Precise Positioning Service, and tens of millions of civil, commercial and scientific users of the Standard Positioning Service.^ See Standard Positioning Service The GPS positioning service available to all users.
  • Micro Modular Technologies - GPS and Wireless Modules - Support 27 January 2010 23:56 UTC www.micro-modular.com [Source type: Reference]

^ Standard Positioning Service (SPS) - The GPS positioning service available to all users.
  • Micro Modular Technologies - GPS and Wireless Modules - Support 27 January 2010 23:56 UTC www.micro-modular.com [Source type: Reference]

^ Satellite maneuvers are not precise by GPS standards.
  • Global Positioning System (GPS) - History, Facts and Pictures 27 January 2010 23:56 UTC www.aviationexplorer.com [Source type: Reference]
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

.In general, GPS receivers are composed of an antenna, tuned to the frequencies transmitted by the satellites, receiver-processors, and a highly-stable clock (often a crystal oscillator).^ L2 Frequency- One of the carrier frequencies transmitted by the GPS satellites.
  • Micro Modular Technologies - GPS and Wireless Modules - Support 27 January 2010 23:56 UTC www.micro-modular.com [Source type: Reference]

^ In general, GPS receivers are composed of an antenna, tuned to the frequencies transmitted by the satellites, receiver-processors, and a highly-stable clock (often a crystal oscillator).
  • Global Positioning System! 27 January 2010 23:56 UTC www.kipaddotta.com [Source type: FILTERED WITH BAYES]

^ Navigation Message- The message transmitted by each GPS satellite.
  • Micro Modular Technologies - GPS and Wireless Modules - Support 27 January 2010 23:56 UTC www.micro-modular.com [Source type: Reference]

.They may also include a display for providing location and speed information to the user.^ They may also include a display for providing location and speed information to the user.
  • Global Positioning System! 27 January 2010 23:56 UTC www.kipaddotta.com [Source type: FILTERED WITH BAYES]
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ This was eliminated by order of President Clinton as it became obvious that civilian and commercial users had many unimagined uses for precise location and timing information as well.

^ Using the GPS receiver, players can acquire their current location and display the exact stars that they should be seeing up in the sky.
  • TGS 06: Sony debuts PSP GPS - News at GameSpot 13 January 2010 11:56 UTC www.gamespot.com [Source type: FILTERED WITH BAYES]

.A receiver is often described by its number of channels: this signifies how many satellites it can monitor simultaneously.^ A receiver is often described by its number of channels: this signifies how many satellites it can monitor simultaneously.
  • Global Positioning System! 27 January 2010 23:56 UTC www.kipaddotta.com [Source type: FILTERED WITH BAYES]
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ Most receivers available are continuous receivers and they can monitor four or more satellites simultaneously, depending on the number of channels available.
  • Precision Farming Tools: Global Positioning System (GPS) - Virginia Cooperative Extension 27 January 2010 23:56 UTC www.ext.vt.edu [Source type: Reference]

^ To do this, the receiver produces an identical C/A sequence using the same seed number, referenced to its local clock, starting at the same time the satellite sent it.
  • Global Positioning System (GPS) - History, Facts and Pictures 27 January 2010 23:56 UTC www.aviationexplorer.com [Source type: Reference]

.Originally limited to four or five, this has progressively increased over the years so that, as of 2007, receivers typically have between 12 and 20 channels.^ Originally limited to four or five, this has progressively increased over the years so that, as of 2007, receivers typically have between 12 and 20 channels.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ Originally limited to four or five, this has progressively increased over the years so that, as of 2006, receivers typically have between twelve and twenty channels.
  • Global Positioning System! 27 January 2010 23:56 UTC www.kipaddotta.com [Source type: FILTERED WITH BAYES]

^ Typical Coast Guard beacon receivers have two channels.
  • WQ452 Precision Agriculture: Global Positioning System | University of Missouri Extension 27 January 2010 23:56 UTC extension.missouri.edu [Source type: Reference]

[37]
A typical OEM GPS receiver module measuring 15×17 mm.
.GPS receivers may include an input for differential corrections, using the RTCM SC-104 format.^ The data portion of the signal may also contain differential corrections that can be used by receivers to correct for GPS errors.
  • NPS GPS Support Facility - Glossary of Common GPS Terms 13 January 2010 11:56 UTC www.nps.gov [Source type: Reference]

^ Correcting a GPS receiver's clock .
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ Special Committee 104 (SC-104) - The RTCM standard defining communication from a Differential GPS beacon receiver and the Differential GPS receiver.
  • Micro Modular Technologies - GPS and Wireless Modules - Support 27 January 2010 23:56 UTC www.micro-modular.com [Source type: Reference]

.This is typically in the form of an RS-232 port at 4,800 bit/s speed.^ This is typically in the form of a RS-232 port at 4,800 bit/s speed.
  • Global Positioning System! 27 January 2010 23:56 UTC www.kipaddotta.com [Source type: FILTERED WITH BAYES]
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

.Data is actually sent at a much lower rate, which limits the accuracy of the signal sent using RTCM. Receivers with internal DGPS receivers can outperform those using external RTCM data.^ Data is actually sent at a much lower rate, which limits the accuracy of the signal sent using RTCM. Receivers with internal DGPS receivers can outperform those using external RTCM data.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ Data are actually sent at a much lower rate, which limits the accuracy of the signal sent using RTCM. Receivers with internal DGPS receivers can outperform those using external RTCM data.
  • Global Positioning System! 27 January 2010 23:56 UTC www.kipaddotta.com [Source type: FILTERED WITH BAYES]

^ This can be accomplished by using a combination of differential GPS (DGPS) correction data, transmitting GPS signal phase information and ambiguity resolution techniques via statistical tests possibly with processing in real-time (real-time kinematic positioning, RTK).
  • Global Positioning System! 27 January 2010 23:56 UTC www.kipaddotta.com [Source type: FILTERED WITH BAYES]

.As of 2006, even low-cost units commonly include Wide Area Augmentation System (WAAS) receivers.^ WAAS - A differential correction system that stands for the "Wide Area Augmentation System."
  • Precision Farming Tools: Global Positioning System (GPS) - Virginia Cooperative Extension 27 January 2010 23:56 UTC www.ext.vt.edu [Source type: Reference]

^ Examples of augmentation systems include the Wide Area Augmentation System, Differential GPS, and Inertial Navigation Systems.
  • Global Positioning System! 27 January 2010 23:56 UTC www.kipaddotta.com [Source type: FILTERED WITH BAYES]

^ As of 2006, even low-cost units commonly include Wide Area Augmentation System (WAAS) receivers.
  • Global Positioning System! 27 January 2010 23:56 UTC www.kipaddotta.com [Source type: FILTERED WITH BAYES]
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

A typical GPS receiver with integrated antenna.
.Many GPS receivers can relay position data to a PC or other device using the NMEA 0183 protocol, or the newer and less widely used NMEA 2000.^ Many GPS receivers can relay position data to a PC or other device using the NMEA 0183 protocol.
  • Global Positioning System! 27 January 2010 23:56 UTC www.kipaddotta.com [Source type: FILTERED WITH BAYES]

^ Some GPS receivers can relay position data to a PC or other device using the NMEA 0183 protocol.
  • GPS GLOBAL POSITIONING SYSTEM 27 January 2010 23:56 UTC www.speedace.info [Source type: FILTERED WITH BAYES]

^ However, the GPS system can be used for many other useful purposes.
  • Global Positioning System - GPS Systems & GPS System 27 January 2010 23:56 UTC www.streetdirectory.com [Source type: General]

[38] .Although these protocols are officially defined by the NMEA,[39] references to these protocols have been compiled from public records, allowing open source tools like gpsd to read the protocol without violating intellectual property laws.^ References to the NMEA protocols have been compiled from public records, allowing open source tools like gpsd to read the protocol without violating intellectual property laws.
  • Global Positioning System! 27 January 2010 23:56 UTC www.kipaddotta.com [Source type: FILTERED WITH BAYES]

^ References to the NMEA protocols have been compiled from public records, allowing open source tools like gpsd to read the protocol without violating Intellectual property laws.
  • GPS GLOBAL POSITIONING SYSTEM 27 January 2010 23:56 UTC www.speedace.info [Source type: FILTERED WITH BAYES]

^ Each of these publications is incorporated by reference herein.
  • Attitude determination using a global positioning system - Patent 6580389 27 January 2010 23:56 UTC www.freepatentsonline.com [Source type: Reference]

.Other proprietary protocols exist as well, such as the SiRF and MTK protocols.^ Other proprietary protocols exist as well, such as the SiRF and MTK protocols.
  • Global Positioning System! 27 January 2010 23:56 UTC www.kipaddotta.com [Source type: FILTERED WITH BAYES]
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ NMEA 0183 protocol with proprietary extension sentences, such as a certain added data command for initiating the request.
  • TRANSFER OF GLOBAL POSITIONING SYSTEM ASSISTANCE DATA - Patent application 27 January 2010 23:56 UTC www.faqs.org [Source type: Reference]

.Receivers can interface with other devices using methods including a serial connection, USB, or Bluetooth.^ Receivers can interface with other devices using methods including a serial connection, USB or Bluetooth.
  • Global Positioning System! 27 January 2010 23:56 UTC www.kipaddotta.com [Source type: FILTERED WITH BAYES]

^ Receivers can interface with other devices using methods including a serial connection, USB or Bluetooth .
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ Includes: GPS 18x Receiver with serial interface cable and 12v.
  • Garmin GPS Units: Portable handheld Car and Marine 13 January 2010 11:56 UTC www.thegpsstore.com [Source type: General]

Navigation

Aspects of navigation are discussed in this section. .The subsection on navigation signals discusses details of the message content.^ The second L-band signal is centered at 1227.60 MHz and carries the P-code and navigation message.
  • NPS GPS Support Facility - Glossary of Common GPS Terms 13 January 2010 11:56 UTC www.nps.gov [Source type: Reference]

^ This signal carries the Coarse Acquisition Code (C/A code), P(Y) Code (Precise code), and the navigation message, and is transmitted on a frequency of 1575.42 MHz.
  • Micro Modular Technologies - GPS and Wireless Modules - Support 27 January 2010 23:56 UTC www.micro-modular.com [Source type: Reference]

^ Even if the receiver can track a signal, it cannot form a position without ephemeris data from the Navigation Message.
  • Micro Modular Technologies - GPS and Wireless Modules - Support 27 January 2010 23:56 UTC www.micro-modular.com [Source type: Reference]

.Carrier frequencies for the messages are stated.^ This signal carries the Coarse Acquisition Code (C/A code), P(Y) Code (Precise code), and the navigation message, and is transmitted on a frequency of 1575.42 MHz.
  • Micro Modular Technologies - GPS and Wireless Modules - Support 27 January 2010 23:56 UTC www.micro-modular.com [Source type: Reference]

.Demodulating the carrier and decoding to separate the signals from the satellites is described.^ Each satellite transmits two carrier signals.
  • Precision Farming Tools: Global Positioning System (GPS) - Virginia Cooperative Extension 27 January 2010 23:56 UTC www.ext.vt.edu [Source type: Reference]

^ Since all of the satellite signals are modulated onto the same L1 carrier frequency, there is a need to separate the signals after demodulation.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ System and method for receiving and decoding global positioning satellite signals .
  • Combining GPS with TOA/TDOA of ... - Google Patent Search 27 January 2010 23:56 UTC www.google.com [Source type: Reference]

.The position calculation subsection does not require an understanding of the other subsections.^ Bonuses comprise the estimation of all other aircraft states like position, velocity and angular rates without requiring multiple gyros or accelerometers onboard.
  • Attitude determination using a global positioning system - Patent 6580389 27 January 2010 23:56 UTC www.freepatentsonline.com [Source type: Reference]

^ The position calculated by a GPS receiver requires the current time, the position of the satellite and the measured delay of the received signal.
  • Global Positioning System! 27 January 2010 23:56 UTC www.kipaddotta.com [Source type: FILTERED WITH BAYES]
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

.Basic equations describing the geometry of the sphere and the fundamental concept that the satellite message travels at the speed of light are used in the subsection.^ Assuming the message traveled at the speed of light, c , the distance traveled, can be computed as .
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ Assume the message travels at the speed of light , then the pseudorange satisfies the equation, .
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ You have set the device to simulator mode, then travel in simulator mode (use a very high speed to save time) or enter the coordinates of the desired position by hand.
  • Global Positioning System 27 January 2010 23:56 UTC michna.com [Source type: FILTERED WITH BAYES]

.The subsection on multidimensional Newton-Raphson may be of interest only to those readers who want a more detailed understanding on how an algorithm might be written and is unnecessary for the reader who is uninterested in this amount of detail.^ For a more detailed description of the mathematics see Multidimensional Newton Raphson .
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ This recalls a story I heard of a man who wanted to know how to turn off the beeps, they frightened his horse.
  • A Practical Guide to GPS -UTM 13 January 2010 11:56 UTC www.dbartlett.com [Source type: FILTERED WITH BAYES]

^ But if you want something more or dislike the performance of TomTom in general then you might want to consider another GPS for your navigation needs.

Navigation signals

.Each GPS satellite continuously broadcasts a Navigation Message at 50 bit/s giving the time-of-week, GPS week number and satellite health information (all transmitted in the first part of the message), an ephemeris (transmitted in the second part of the message) and an almanac (later part of the message).^ GPS and satellite navigation system .
  • Combining GPS with TOA/TDOA of ... - Google Patent Search 27 January 2010 23:56 UTC www.google.com [Source type: Reference]

^ Each GPS satellite has an atomic clock, and continually transmits messages containing the current time at the start of the message, parameters to calculate the location of the satellite (the ephemeris), and the general system health (the almanac).
  • Global Positioning System (GPS) - History, Facts and Pictures 27 January 2010 23:56 UTC www.aviationexplorer.com [Source type: Reference]

^ First GPS satellite was launched in 1978.
  • Precision Farming Tools: Global Positioning System (GPS) - Virginia Cooperative Extension 27 January 2010 23:56 UTC www.ext.vt.edu [Source type: Reference]

.The messages are sent in frames, each taking 30 seconds to transmit 1,500 bits.^ The message data is transmitted at 50 bits per second.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ The messages are sent in frames, each taking 30 seconds to transmit 1500 bits.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ The almanac consists of coarse orbit and status information for each satellite in the constellation and takes 12 seconds for each satellite present, with information for a new satellite being transmitted every 30 seconds (15.5 minutes for 31 satellites).
  • Global Positioning System! 27 January 2010 23:56 UTC www.kipaddotta.com [Source type: FILTERED WITH BAYES]

.Transmission of each 30 second frame begins precisely on the minute and half minute as indicated by the satellite's atomic clock according to Satellite message format.^ Transmission of each 30 second frame begins precisely on the minute and half minute as indicated by the satellite's atomic clock according to Satellite message format .
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ After the merger couple of times, and then configure the settings for sensitivityhave begun to pick up signals from satellite receiver with a delay of 30, 60, 120 and more seconds.

^ The atomic clocks on board the GPS satellites are precisely tuned, making the system a practical engineering application of the scientific theory of relativity in a real-world environment.
  • Global Positioning System! 27 January 2010 23:56 UTC www.kipaddotta.com [Source type: FILTERED WITH BAYES]

.Each frame contains 5 subframes of length 6 seconds and with 300 bits.^ Each frame contains 5 subframes of length 6 seconds and with 300 bits.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ Each subframe contains 10 words of 30 bits with length 0.6 seconds each.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ Also each subframe of the navigation frame is identified by bits in the Handover Word (HOW) thereby enabling the receiver to determine which subframe (see section 1.4.2.6 of and section 2.5.4 of "Essentials of Satellite Navigation Compendium" ).
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

.Each subframe contains 10 words of 30 bits with length 0.6 seconds each.^ Each frame contains 5 subframes of length 6 seconds and with 300 bits.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ Words 3 through 10 of subframes 4 and 5 contain a new part of the almanac.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ Each subframe contains 10 words of 30 bits with length 0.6 seconds each.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

.Words 1 and 2 of every subframe have the same type of data.^ Words 1 and 2 of every subframe have the same type of data.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ After a subframe has been read and interpreted, the time the next subframe was sent can be calculated through the use of the clock correction data and the HOW word.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ Words 3 through 10 of subframe 1 contain data describing the satellite clock and its relationship to GPS time.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

.The first word is the telemetry word which indicates the beginning of a subframe and is used by the receiver to synch with the navigation message.^ The first word is the telemetry word which indicates the beginning of a subframe and is used by the receiver to synch with the navigation message.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ Each subframe of the navigation frame begins with a Telemetry Word which enables the receiver to detect the beginning of a subframe and determine the receiver clock time at which the navigation subframe begins.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ This indicates the beginning of a data bit of the navigation message (see section 1.4.2.5 of ).
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

.The second word is the HOW or handover word and it contains timing information which enables the receiver to identify the subframe and provides the time the next subframe was sent.^ The second word is the HOW or handover word and it contains timing information which enables the receiver to identify the subframe and provides the time the next subframe was sent.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ Each subframe contains 10 words of 30 bits with length 0.6 seconds each.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ These receivers provide real-time situational awareness for the warfighter much more quickly and accurately than previous, conventional methods.

.Words 3 through 10 of subframe 1 contain data describing the satellite clock and its relationship to GPS time.^ GPS satellites contain multiple cesium and rubidium clocks.
  • Micro Modular Technologies - GPS and Wireless Modules - Support 27 January 2010 23:56 UTC www.micro-modular.com [Source type: Reference]

^ Words 3 through 10 of subframes 4 and 5 contain a new part of the almanac.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ Each subframe contains 10 words of 30 bits with length 0.6 seconds each.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

.Words 3 through 10 of subframes 2 and 3, contain the ephemeris data, giving the satellite's own precise orbit.^ Words 3 through 10 of subframes 4 and 5 contain a new part of the almanac.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ Each subframe contains 10 words of 30 bits with length 0.6 seconds each.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ Ephemeris- A data set of precise orbit information for a GPS satellite.
  • Micro Modular Technologies - GPS and Wireless Modules - Support 27 January 2010 23:56 UTC www.micro-modular.com [Source type: Reference]

.The ephemeris is updated every 2 hours and is generally valid for 4 hours, with provisions for updates every 6 hours or longer in non-nominal conditions.^ The ephemeris is updated every 2 hours and is generally valid for 4 hours, with provisions for 6 hour time-outs.
  • Global Positioning System! 27 January 2010 23:56 UTC www.kipaddotta.com [Source type: FILTERED WITH BAYES]

^ The ephemeris is updated every 2 hours and is generally valid for 4 hours, with provisions for updates every 6 hours or longer in non-nominal conditions.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ The MCS computes precise, updated information on the satellites orbits and clock status every 15 minutes, 24 hours a day, seven days a week.

.The time needed to acquire the ephemeris is becoming a significant element of the delay to first position fix, because, as the hardware becomes more capable, the time to lock onto the satellite signals shrinks, but the ephemeris data requires 30 seconds (worst case) before it is received, due to the low data transmission rate.^ System and method for receiving and decoding global positioning satellite signals .
  • Combining GPS with TOA/TDOA of ... - Google Patent Search 27 January 2010 23:56 UTC www.google.com [Source type: Reference]

^ Time determination in satellite positioning system receivers and methods therefor .
  • Combining GPS with TOA/TDOA of ... - Google Patent Search 27 January 2010 23:56 UTC www.google.com [Source type: Reference]

^ The time needed to acquire the ephemeris is becoming a significant element of the delay to first position fix, because, as the hardware becomes more capable, the time to lock onto the satellite signals shrinks, but the ephemeris data requires 30 seconds (worst case) before it is received, due to the low data transmission rate.
  • Global Positioning System! 27 January 2010 23:56 UTC www.kipaddotta.com [Source type: FILTERED WITH BAYES]
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

.The almanac consists of coarse orbit and status information for each satellite in the constellation, an ionospheric model, and information to relate GPS derived time to Coordinated Universal Time (UTC).^ Constellation- The set of GPS satellites in orbit.
  • Micro Modular Technologies - GPS and Wireless Modules - Support 27 January 2010 23:56 UTC www.micro-modular.com [Source type: Reference]

^ Artist's conception of GPS satellite in orbit .
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ Ephemeris- A data set of precise orbit information for a GPS satellite.
  • Micro Modular Technologies - GPS and Wireless Modules - Support 27 January 2010 23:56 UTC www.micro-modular.com [Source type: Reference]

.Words 3 through 10 of subframes 4 and 5 contain a new part of the almanac.^ Words 3 through 10 of subframes 4 and 5 contain a new part of the almanac.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ Each subframe contains 10 words of 30 bits with length 0.6 seconds each.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ After a subframe has been read and interpreted, the time the next subframe was sent can be calculated through the use of the clock correction data and the HOW word.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

.Each frame contains 1/25th of the almanac, so 12.5 minutes are required to receive the entire almanac from a single satellite.^ Each frame contains 1/25th of the almanac, so 12.5 minutes are required to receive the entire almanac from a single satellite.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ The almanac consists of coarse orbit and status information for each satellite in the constellation and takes 12 seconds for each satellite present, with information for a new satellite being transmitted every 30 seconds (15.5 minutes for 31 satellites).
  • Global Positioning System! 27 January 2010 23:56 UTC www.kipaddotta.com [Source type: FILTERED WITH BAYES]

^ It is transmitted by each GPS satellite over a 12.5 minute period to facilitate acquisition of satellites by GPS receivers.
  • Micro Modular Technologies - GPS and Wireless Modules - Support 27 January 2010 23:56 UTC www.micro-modular.com [Source type: Reference]

[40] .The almanac serves several purposes.^ The almanac serves several purposes.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

.The first is to assist in the acquisition of satellites at power-up by allowing the receiver to generate a list of visible satellites based on stored position and time, while an ephemeris from each satellite is needed to compute position fixes using that satellite.^ The first is to assist in the acquisition of satellites at power-up by allowing the receiver to generate a list of visible satellites based on stored position and time, while an ephemeris from each satellite is needed to compute position fixes using that satellite.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ Acquisition Time- Period required by a GPS receiver to determine initial position based on acquisition of satellite signals.
  • Micro Modular Technologies - GPS and Wireless Modules - Support 27 January 2010 23:56 UTC www.micro-modular.com [Source type: Reference]

^ GPS is a satellite-based positioning system used for navigation, relative positioning, and time transfer.
  • Magellan GPS Receiver, Global Positioning Systems, Geodetic Base Station Software, Differential GPS 9 October 2009 7:11 UTC www.idsemergencymanagement.com [Source type: FILTERED WITH BAYES]

.In older hardware, lack of an almanac in a new receiver would cause long delays before providing a valid position, because the search for each satellite was a slow process.^ This process is repeated for each satellite to which the receiver is listening.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ In older hardware, lack of an almanac in a new receiver would cause long delays before providing a valid position, because the search for each satellite was a slow process.
  • Global Positioning System! 27 January 2010 23:56 UTC www.kipaddotta.com [Source type: FILTERED WITH BAYES]
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ The existing new satellites are positioned near the old satellites to provide better redundancy, but instead the plan is to spread those satellites out to make the overall enhancements.
  • GPS Lodge - GPS reviews, GPS, GPS Receiver, Global Positioning System, Garmin, Etrex, Etrex Legend, Etrex Vista, Etrexm, Summit, GPSMap, Geko, Foretrex, Streetpilot, Magellan, eXplorist, Meridian, Mapsend, GPS Auto, GPS Automobile, Car GPS, Lowrance GPS, Mio GPS 13 January 2010 11:56 UTC gpslodge.com [Source type: General]

.Advances in hardware have made the acquisition process much faster, so not having an almanac is no longer an issue.^ Advances in hardware have made the acquisition process much faster, so not having an almanac is no longer an issue.
  • Global Positioning System! 27 January 2010 23:56 UTC www.kipaddotta.com [Source type: FILTERED WITH BAYES]
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ Faster location acquisition Less processing power is required by the device Saves battery life Location acquisition indoors or in non-optimal environmental settings .
  • GPS vs. aGPS: A Quick Tutorial | WMExperts 13 January 2010 11:56 UTC www.wmexperts.com [Source type: FILTERED WITH BAYES]

^ But when you use assisted GPS this whole process is much faster.
  • GPS vs. aGPS: A Quick Tutorial | WMExperts 13 January 2010 11:56 UTC www.wmexperts.com [Source type: FILTERED WITH BAYES]

.The second purpose is for relating time derived from the GPS (called GPS time) to the international time standard of UTC.^ GPS time is directly relatable to UTC: UTC-GPS = seconds.
  • NPS GPS Support Facility - Glossary of Common GPS Terms 13 January 2010 11:56 UTC www.nps.gov [Source type: Reference]

^ The second purpose is for relating time derived from the GPS (called GPS time) to the international time standard of UTC .
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ The lack of corrections means that GPS time remains at a constant offset (TAI - GPS = 19 seconds) with International Atomic Time (TAI).
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

.Finally, the almanac allows a single-frequency receiver to correct for ionospheric error by using a global ionospheric model.^ Finally, the almanac allows a single-frequency receiver to correct for ionospheric error by using a global ionospheric model.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ The GPS satellites broadcast signals on two different frequencies so that sophisticated user receivers can correct for distortion effects due to the ionosphere, a layer of the atmosphere several hundred miles above the Earth.

^ Since the GPS receiver computes its approximate altitude, this error is relatively simple to correct, either by applying a function regression or correlating margin of atmospheric error to ambient pressure using a barometric altimeter.
  • Global Positioning System (GPS) - History, Facts and Pictures 27 January 2010 23:56 UTC www.aviationexplorer.com [Source type: Reference]
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

.The corrections are not as accurate as augmentation systems like WAAS or dual-frequency receivers.^ The corrections are not as accurate as augmentation systems like WAAS or dual-frequency receivers.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ The ionospheric data are transmitted via satellite in Satellite Based Augmentation Systems such as WAAS, which transmits it on the GPS frequency using a special pseudo-random noise sequence (PRN), so only one receiver and antenna are required.
  • Global Positioning System (GPS) - History, Facts and Pictures 27 January 2010 23:56 UTC www.aviationexplorer.com [Source type: Reference]

^ However, it is often better than no correction, since ionospheric error is the largest error source for a single-frequency GPS receiver.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

.However, it is often better than no correction, since ionospheric error is the largest error source for a single-frequency GPS receiver.^ However, it is often better than no correction, since ionospheric error is the largest error source for a single-frequency GPS receiver.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ GPS Accuracy and error sources .
  • Global Positioning System! 27 January 2010 23:56 UTC www.kipaddotta.com [Source type: FILTERED WITH BAYES]

^ Finally, the almanac allows a single-frequency receiver to correct for ionospheric error by using a global ionospheric model.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

.An important thing to note about navigation data is that each satellite transmits not only its own ephemeris, but transmits an almanac for all satellites.^ See Almanac Errors in the ephemeris data transmitted by a GPS satellite.
  • Micro Modular Technologies - GPS and Wireless Modules - Support 27 January 2010 23:56 UTC www.micro-modular.com [Source type: Reference]

^ An important thing to note about navigation data is that each satellite transmits not only its own ephemeris , but transmits an almanac for all satellites.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ Also includes satellite almanac data.
  • GPS GLOBAL POSITIONING SYSTEM 27 January 2010 23:56 UTC www.speedace.info [Source type: FILTERED WITH BAYES]

.All satellites broadcast at the same two frequencies, 1.57542 GHz (L1 signal) and 1.2276 GHz (L2 signal).^ GPS satellites broadcast on two links to users: L1 and L2.

^ The GPS satellites broadcast signals on two different frequencies so that sophisticated user receivers can correct for distortion effects due to the ionosphere, a layer of the atmosphere several hundred miles above the Earth.

^ The payload included two L-Band navigation signals at 1575.42 MHz (L1) and 1227.60 MHz (L2).
  • GPS Block 2 and 2A 27 January 2010 23:56 UTC www.astronautix.com [Source type: FILTERED WITH BAYES]

.The receiver can distinguish the signals from different satellites because GPS uses a code division multiple access (CDMA) spread-spectrum technique where the low-bitrate message data is encoded with a high-rate pseudo-random (PRN) sequence that is different for each satellite.^ The receiver can distinguish the signals from different satellites because GPS uses a code division multiple access (CDMA) spread-spectrum technique where the low-bitrate message data is encoded with a high-rate pseudo-random (PRN) sequence that is different for each satellite.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ Spread spectrum receiver performance improvement .
  • Combining GPS with TOA/TDOA of ... - Google Patent Search 27 January 2010 23:56 UTC www.google.com [Source type: Reference]

^ A measurement of the difference in phase between the received GPS PRN code and the PRN code generated internally in the receiver.
  • Micro Modular Technologies - GPS and Wireless Modules - Support 27 January 2010 23:56 UTC www.micro-modular.com [Source type: Reference]

.The receiver knows the PRN codes for each satellite and can use this to reconstruct the actual message data.^ The receiver knows the PRN codes for each satellite and can use this to reconstruct the actual message data.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ The receiver can distinguish the signals from different satellites because GPS uses a code division multiple access (CDMA) spread-spectrum technique where the low-bitrate message data is encoded with a high-rate pseudo-random (PRN) sequence that is different for each satellite.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ Each satellite has its own C/A code so that it can be uniquely identified and received separately from the other satellites transmitting on the same frequency.
  • Global Positioning System! 27 January 2010 23:56 UTC www.kipaddotta.com [Source type: FILTERED WITH BAYES]

.The message data is transmitted at 50 bits per second.^ The message data is transmitted at 50 bits per second.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ The week number is transmitted as a ten-bit field in the C/A and P(Y) navigation messages, and so it becomes zero again every 1,024 weeks (19.6 years).
  • Global Positioning System! 27 January 2010 23:56 UTC www.kipaddotta.com [Source type: FILTERED WITH BAYES]

^ The civilian code comprises a 50 bs -1 radio signal transmitted at 1,575.42 MHz carrying three signals: a pseudo-random code, ephemeris data, and almanac data.
  • International Journal of Health Geographics | Full text | Development of a wearable global positioning system for place and health research 27 January 2010 23:56 UTC www.ij-healthgeographics.com [Source type: Academic]

.Two distinct CDMA encodings are used: the coarse/acquisition (C/A) code (a so-called Gold code) at 1.023 million chips per second, and the precise (P) code at 10.23 million chips per second.^ Two distinct CDMA encodings are used: the coarse/acquisition (C/A) code (a so-called Gold code ) at 1.023 million chips per second, and the precise (P) code at 10.23 million chips per second.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ Number of chips per second.
  • NPS GPS Support Facility - Glossary of Common GPS Terms 13 January 2010 11:56 UTC www.nps.gov [Source type: Reference]

^ The standard deviations, , for the coarse/acquisition and precise codes are also shown in the table.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

.The L1 carrier is modulated by both the C/A and P codes, while the L2 carrier is only modulated by the P code.^ L2 is transmitted at a frequency of 1227.6 MHz and carries only the P(Y) code.

^ The L1 carrier is modulated by both the C/A and P codes, while the L2 carrier is only modulated by the P code.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ Typically, commercial receivers use the single frequency L1 C/A code only.
  • Micro Modular Technologies - GPS and Wireless Modules - Support 27 January 2010 23:56 UTC www.micro-modular.com [Source type: Reference]

[41] .The C/A code is public and used by civilian GPS receivers, while the P code can be encrypted as a so-called P(Y) code which is only available to military equipment with a proper decryption key.^ The precise or precision code of the GPS signal, typically used alone by U.S. and allied military receivers.
  • NPS GPS Support Facility - Glossary of Common GPS Terms 13 January 2010 11:56 UTC www.nps.gov [Source type: Reference]

^ GPS tours are also an example of civilian use.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ P-Code- The precise code of the GPS signal typically used only by the U.S. military.
  • Micro Modular Technologies - GPS and Wireless Modules - Support 27 January 2010 23:56 UTC www.micro-modular.com [Source type: Reference]

.Both the C/A and P(Y) codes impart the precise time-of-day to the user.^ Locations are calculated not in three-dimensional space, but in four-dimensional spacetime, meaning a measure of the precise time-of-day is very important.
  • Global Positioning System! 27 January 2010 23:56 UTC www.kipaddotta.com [Source type: FILTERED WITH BAYES]

^ The military users have access to both the C/A code on L1 and the P(Y) code on L1 and L2.

^ This was eliminated by order of President Clinton as it became obvious that civilian and commercial users had many unimagined uses for precise location and timing information as well.

Satellite frequencies

.
  • L1 (1575.42 MHz): Mix of Navigation Message, coarse-acquisition (C/A) code and encrypted precision P(Y) code, plus the new L1C on future Block III satellites.
  • L2 (1227.60 MHz): P(Y) code, plus the new L2C code on the Block IIR-M and newer satellites since 2005.
  • L3 (1381.05 MHz): Used by the Nuclear Detonation (NUDET) Detection System Payload (NDS) to signal detection of nuclear detonations and other high-energy infrared events.^ L1 (1575.42 MHz ): Mix of Navigation Message, coarse-acquisition (C/A) code and encrypted precision P(Y) code, plus the new L1C on future Block III satellites.
    • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

    ^ This signal carries the P(Y) Code (Precise code) and is transmitted on a frequency of 1227.6 MHz.
    • Micro Modular Technologies - GPS and Wireless Modules - Support 27 January 2010 23:56 UTC www.micro-modular.com [Source type: Reference]

    ^ New civilian signals are called L2C , L5 and L1C ; the new military code is called M-Code .
    • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

    .Used to enforce nuclear test ban treaties.
  • L4 (1379.913 MHz): Being studied for additional ionospheric correction.
  • L5 (1176.45 MHz): Proposed for use as a civilian safety-of-life (SoL) signal (see GPS modernization).^ Used to enforce nuclear test ban treaties.
    • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

    ^ L4 (1379.913 MHz): Being studied for additional ionospheric correction.
    • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

    ^ GPS tours are also an example of civilian use.
    • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

    .This frequency falls into an internationally protected range for aeronautical navigation, promising little or no interference under all circumstances.^ This frequency falls into an internationally protected range for aeronautical navigation, promising little or no interference under all circumstances.
    • GPS GLOBAL POSITIONING SYSTEM 27 January 2010 23:56 UTC www.speedace.info [Source type: FILTERED WITH BAYES]
    • Global Positioning System! 27 January 2010 23:56 UTC www.kipaddotta.com [Source type: FILTERED WITH BAYES]
    • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

    ^ Multiple frequency antenna structures and methods for receiving navigation or ranging signals .
    • Combining GPS with TOA/TDOA of ... - Google Patent Search 27 January 2010 23:56 UTC www.google.com [Source type: Reference]

    ^ The Thales Navigation Aquarius dual-frequency receiver with LRK (Long Range Kinematic) technology provides astonishing performance for dredging applications.
    • Magellan GPS Receiver, Global Positioning Systems, Geodetic Base Station Software, Differential GPS 9 October 2009 7:11 UTC www.idsemergencymanagement.com [Source type: FILTERED WITH BAYES]

    The first Block IIF satellite that would provide this signal is set to be launched in 2010.[42]

C/A code

Demodulation and decoding

Demodulating and Decoding GPS Satellite Signals using the Coarse/Acquisition Gold code.
.Since all of the satellite signals are modulated onto the same L1 carrier frequency, there is a need to separate the signals after demodulation.^ Since all of the satellite signals are modulated onto the same L1 carrier frequency, there is a need to separate the signals after demodulation.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ L1 Frequency- One of the carrier frequencies transmitted by the GPS satellites.
  • Micro Modular Technologies - GPS and Wireless Modules - Support 27 January 2010 23:56 UTC www.micro-modular.com [Source type: Reference]

^ All satellites broadcast at the same two frequencies, 1.57542 GHz (L1 signal) and 1.2276 GHz (L2 signal).
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

.This is done by assigning each satellite a unique binary sequence known as a Gold code, and the signals are decoded, after demodulation, using modulo 2 addition of the Gold codes corresponding to satellites n1 through nk, where k is the number of channels in the GPS receiver and n1 through nk are the PRN identifiers of the satellites.^ The Gold codes used in GPS are a sequence of 1023 bits with a period of one millisecond.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ The receiver uses the C/A Gold code with the same PRN number as the satellite to compute an offset, O, that generates the best correlation.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ A typical GPS receiver calculates its position using the signals from four or more GPS satellites.
  • Global Positioning System (GPS) - History, Facts and Pictures 27 January 2010 23:56 UTC www.aviationexplorer.com [Source type: Reference]

.Each satellite's PRN identifier is unique and in the range from 1 through 32.[43] The results of these modulo 2 additions are the 50 bit/s navigation messages from satellites n1 through nk.^ The results of these modulo 2 additions are the 50 bit/s navigation messages from satellites n 1 through n k .
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ Navigation Message- The message transmitted by each GPS satellite.
  • Micro Modular Technologies - GPS and Wireless Modules - Support 27 January 2010 23:56 UTC www.micro-modular.com [Source type: Reference]

^ Each satellite has its own C/A code so that it can be uniquely identified and received separately from the other satellites transmitting on the same frequency.
  • Global Positioning System! 27 January 2010 23:56 UTC www.kipaddotta.com [Source type: FILTERED WITH BAYES]

.The Gold codes used in GPS are a sequence of 1,023 bits with a period of one millisecond.^ The Gold codes used in GPS are a sequence of 1023 bits with a period of one millisecond.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ Basic and simple to use Rating:3 out of 5 stars This case is easy to use but may be a little short for the 4″ wide GPS systems as they stick out a bit.
  • Garmin 3.5Inch Carrying Case | Ultra Gps 16 January 2010 16:26 UTC ultra-gps.com [Source type: FILTERED WITH BAYES]

^ The ionospheric data are transmitted via satellite in Satellite Based Augmentation Systems such as WAAS, which transmits it on the GPS frequency using a special pseudo-random noise sequence (PRN), so only one receiver and antenna are required.
  • Global Positioning System (GPS) - History, Facts and Pictures 27 January 2010 23:56 UTC www.aviationexplorer.com [Source type: Reference]

.These Gold codes are highly mutually orthogonal, so that it is unlikely that one satellite signal will be misinterpreted as another.^ These Gold codes are highly mutually orthogonal, so that it is unlikely that one satellite signal will be misinterpreted as another.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ These effects are smallest when the satellite is directly overhead and become greater for satellites nearer the horizon since the signal is affected for a longer time.
  • Global Positioning System! 27 January 2010 23:56 UTC www.kipaddotta.com [Source type: FILTERED WITH BAYES]

^ The Gold codes used in GPS are a sequence of 1023 bits with a period of one millisecond.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

.As well, the Gold codes have good auto-correlation properties.^ As well, the Gold codes have good auto-correlation properties.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ The receiver uses the C/A Gold code with the same PRN number as the satellite to compute an offset, O, that generates the best correlation.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ Gold Code- A subset of Pseudo-Random Numbers with low cross-correlation properties (used for GPS PRNs).
  • Micro Modular Technologies - GPS and Wireless Modules - Support 27 January 2010 23:56 UTC www.micro-modular.com [Source type: Reference]

[44]
.There are 1,025 different Gold codes of length 1,023 bits, but only 32 are used.^ There are 1025 different Gold codes of length 1023 bits, but only 32 are used.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ Typically, commercial receivers use the single frequency L1 C/A code only.
  • Micro Modular Technologies - GPS and Wireless Modules - Support 27 January 2010 23:56 UTC www.micro-modular.com [Source type: Reference]

^ The Gold codes used in GPS are a sequence of 1023 bits with a period of one millisecond.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

.These Gold codes are quite often referred to as pseudo random noise since they contain no data and are said to look like random sequences[45].^ A signal with properties like random noise, however it is a defined sequence of 1's and 0's.
  • Micro Modular Technologies - GPS and Wireless Modules - Support 27 January 2010 23:56 UTC www.micro-modular.com [Source type: Reference]

^ Pseudo-Random Noise (PRN) - A signal with properties like random noise, however it is a defined sequence of 1's and 0's.
  • Micro Modular Technologies - GPS and Wireless Modules - Support 27 January 2010 23:56 UTC www.micro-modular.com [Source type: Reference]

^ These Gold codes are quite often referred to as pseudo random noise since they contain no data and are said to look like random sequences.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

.However, this may be misleading since they are actually deterministic sequences.^ However, this may be misleading since they are actually deterministic sequences.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ The navigation message contains corrections for these errors and estimates of the accuracy of the atomic clock, however they are based on observations and may not indicate the clock's current state.
  • Global Positioning System (GPS) - History, Facts and Pictures 27 January 2010 23:56 UTC www.aviationexplorer.com [Source type: Reference]

^ Since the carrier frequency received can vary due to Doppler shift, the points where received PRN sequences begin may not differ from O by an exact integral number of milliseconds.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

.If the almanac information has previously been acquired, the receiver picks which satellites to listen for by their PRNs.^ To start off, the receiver picks which C/A codes to listen for by PRN number, based on the almanac information it has previously acquired.
  • Global Positioning System! 27 January 2010 23:56 UTC www.kipaddotta.com [Source type: FILTERED WITH BAYES]
  • Global Positioning System (GPS) - History, Facts and Pictures 27 January 2010 23:56 UTC www.aviationexplorer.com [Source type: Reference]

^ This process is repeated for each satellite to which the receiver is listening.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ The receiver can then acquire the almanac and determine the satellites it should listen for.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

.If the almanac information is not in memory, the receiver enters a search mode and cycles through the PRN numbers until a lock is obtained on one of the satellites.^ If the almanac information is not in memory, the receiver enters a search mode and cycles through the PRN numbers until a lock is obtained on one of the satellites.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ If the almanac information has previously been acquired, the receiver picks which satellites to listen for by their PRN numbers.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ In order to measure the delay, the satellite repeatedly sends a 1,023 bit long pseudo random sequence; the receiver calculates an identical sequence from a known seed number, and shifts it until the two sequences match.
  • GPS GLOBAL POSITIONING SYSTEM 27 January 2010 23:56 UTC www.speedace.info [Source type: FILTERED WITH BAYES]

.To obtain a lock, it is necessary that there be an unobstructed line of sight from the receiver to the satellite.^ To obtain a lock, it is necessary that there be an unobstructed line of sight from the receiver to the satellite.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ Because of this, carrier frequency tracking along with PRN code tracking are used to determine when the received satellite's PRN code begins (see "How a GPS Receiver Gets a Lock" ).
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ While a minimum of four receiving channels is necessary for parallel processing, the extra ones are used to keep track of whatever satellites are in view and to be ready to replace one of the four being used.
  • A Practical Guide to GPS -UTM 13 January 2010 11:56 UTC www.dbartlett.com [Source type: FILTERED WITH BAYES]

.The receiver can then acquire the almanac and determine the satellites it should listen for.^ This process is repeated for each satellite to which the receiver is listening.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ The receiver can then acquire the almanac and determine the satellites it should listen for.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ If the almanac information has previously been acquired, the receiver picks which satellites to listen for by their PRN numbers.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

.As it detects each satellite's signal, it identifies it by its distinct C/A code pattern.^ As it detects each satellite's signal, it identifies it by its distinct C/A code pattern, then measures the time delay for each satellite.
  • Global Positioning System! 27 January 2010 23:56 UTC www.kipaddotta.com [Source type: FILTERED WITH BAYES]

^ As it detects each satellite's signal, it identifies it by its distinct C/A code pattern.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ As it detects each satellite's signal, it identifies it by its distinct C/A code pattern, then measures the received time for each satellite.
  • Global Positioning System (GPS) - History, Facts and Pictures 27 January 2010 23:56 UTC www.aviationexplorer.com [Source type: Reference]

.The receiver uses the C/A Gold code with the same PRN number as the satellite to compute an offset, O, that generates the best correlation.^ It then computes the offset to the local clock that generates the maximum correlation.
  • Global Positioning System (GPS) - History, Facts and Pictures 27 January 2010 23:56 UTC www.aviationexplorer.com [Source type: Reference]

^ To do this, the receiver produces an identical C/A sequence using the same seed number as the satellite.
  • Global Positioning System! 27 January 2010 23:56 UTC www.kipaddotta.com [Source type: FILTERED WITH BAYES]

^ Since the GPS receiver computes its approximate altitude, this error is relatively simple to correct, either by applying a function regression or correlating margin of atmospheric error to ambient pressure using a barometric altimeter.
  • Global Positioning System (GPS) - History, Facts and Pictures 27 January 2010 23:56 UTC www.aviationexplorer.com [Source type: Reference]

.The offset, O, is computed in a trial and error manner.^ The offset, O, is computed in a trial and error manner.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

.The 1,023 bits of the satellite PRN signal are compared with the receiver PRN signal.^ The 1023 bits of the satellite PRN signal are compared with the receiver PRN signal.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ Because of this, carrier frequency tracking along with PRN code tracking are used to determine when the received satellite's PRN code begins (see "How a GPS Receiver Gets a Lock" ).
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ By comparing the rising and trailing edges of the bit transitions, modern electronics can measure signal offset to within about 1% of a bit time, or approximately 10 nanoseconds for the C/A code.
  • Global Positioning System! 27 January 2010 23:56 UTC www.kipaddotta.com [Source type: FILTERED WITH BAYES]

.If correlation is not achieved, the 1,023 bits of the receiver's internally generated PRN code are shifted by one bit relative to the satellite's PRN code and the signals are again compared.^ A measurement of the difference in phase between the received GPS PRN code and the PRN code generated internally in the receiver.
  • Micro Modular Technologies - GPS and Wireless Modules - Support 27 January 2010 23:56 UTC www.micro-modular.com [Source type: Reference]

^ Code phase- A measurement of the difference in phase between the received GPS PRN code and the PRN code generated internally in the receiver.
  • Micro Modular Technologies - GPS and Wireless Modules - Support 27 January 2010 23:56 UTC www.micro-modular.com [Source type: Reference]

^ If correlation is not achieved, the 1023 bits of the receiver's internally generated PRN code are shifted by one bit relative to the satellite's PRN code and the signals are again compared.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

.This process is repeated until correlation is achieved or all 1,023 possible cases have been tried.^ This process is repeated until correlation is achieved or all 1023 possible cases have been tried (see "How a GPS Receiver Gets a Lock" ).
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ If all 1023 cases have been tried without achieving correlation, the frequency oscillator is offset to the next value and the process is repeated.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ I tried to have ANTOnline either accept it back as a return or an exchange for the correct case (see Garmin website for the correct case)but they ignored all my requests until they finally emailed me to tell me they contacted Garmin who will work with me to correct the matter.
  • Garmin 3.5Inch Carrying Case | Ultra Gps 16 January 2010 16:26 UTC ultra-gps.com [Source type: FILTERED WITH BAYES]

[46] .If all 1,023 cases have been tried without achieving correlation, the frequency oscillator is offset to the next value and the process is repeated.^ If all 1023 cases have been tried without achieving correlation, the frequency oscillator is offset to the next value and the process is repeated.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ This process is repeated until correlation is achieved or all 1023 possible cases have been tried (see "How a GPS Receiver Gets a Lock" ).
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

.Since the carrier frequency received can vary due to Doppler shift, the points where received PRN sequences begin may not differ from O by an exact integral number of milliseconds.^ Since the carrier frequency received can vary due to Doppler shift, the points where received PRN sequences begin may not differ from O by an exact integral number of milliseconds.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ In order to measure the delay, the satellite repeatedly sends a 1,023 bit long pseudo random sequence; the receiver calculates an identical sequence from a known seed number, and shifts it until the two sequences match.
  • GPS GLOBAL POSITIONING SYSTEM 27 January 2010 23:56 UTC www.speedace.info [Source type: FILTERED WITH BAYES]

^ The GPS satellites broadcast signals on two different frequencies so that sophisticated user receivers can correct for distortion effects due to the ionosphere, a layer of the atmosphere several hundred miles above the Earth.

.Because of this, carrier frequency tracking along with PRN code tracking are used to determine when the received satellite's PRN code begins.^ Each satellite has its own C/A code so that it can be uniquely identified and received separately from the other satellites transmitting on the same frequency.
  • Global Positioning System! 27 January 2010 23:56 UTC www.kipaddotta.com [Source type: FILTERED WITH BAYES]

^ L2 Frequency- One of the carrier frequencies transmitted by the GPS satellites.
  • Micro Modular Technologies - GPS and Wireless Modules - Support 27 January 2010 23:56 UTC www.micro-modular.com [Source type: Reference]

^ Typically, commercial receivers use the single frequency L1 C/A code only.
  • Micro Modular Technologies - GPS and Wireless Modules - Support 27 January 2010 23:56 UTC www.micro-modular.com [Source type: Reference]

[46] .Unlike the earlier computation of offset in which trials of all 1,023 offsets could potentially be required, the tracking to maintain lock usually requires shifting of half a pulse width or less.^ Unlike cellular tracking systems, there are no subscriptions or setup fees required to use the device.
  • GPS dog collars, tracking your lost dog or pet, GPS tracking systems, GPS tracking device, GPS tracking, 13 January 2010 11:56 UTC www.gpsdogcollartracking.com [Source type: General]

.To perform this tracking, the receiver observes two quantities, phase error and received frequency offset.^ Cycle slip- A discontinuity of an interger number of cycles in the measured carrier phase due to a temporary loss-of-lock in the carrier tracking loop of a GPS receiver.
  • Micro Modular Technologies - GPS and Wireless Modules - Support 27 January 2010 23:56 UTC www.micro-modular.com [Source type: Reference]

^ A change in the observed frequency of a wave, occurring when the receiver and transmitter are in motion relative to each other, with the frequency increasing when the source and observer approach each other and decreasing when they move apart.
  • Micro Modular Technologies - GPS and Wireless Modules - Support 27 January 2010 23:56 UTC www.micro-modular.com [Source type: Reference]

^ Accurate measurement of the relative positions of two receivers tracking the same GPS signals.
  • Micro Modular Technologies - GPS and Wireless Modules - Support 27 January 2010 23:56 UTC www.micro-modular.com [Source type: Reference]

.The correlation of the received PRN code with respect to the receiver generated PRN code is computed to determine if the bits of the two signals are misaligned.^ It then computes the offset to the local clock that generates the maximum correlation.
  • Global Positioning System (GPS) - History, Facts and Pictures 27 January 2010 23:56 UTC www.aviationexplorer.com [Source type: Reference]

^ The precise or precision code of the GPS signal, typically used alone by U.S. and allied military receivers.
  • NPS GPS Support Facility - Glossary of Common GPS Terms 13 January 2010 11:56 UTC www.nps.gov [Source type: Reference]

^ Accurate measurement of the relative positions of two receivers tracking the same GPS signals.
  • Micro Modular Technologies - GPS and Wireless Modules - Support 27 January 2010 23:56 UTC www.micro-modular.com [Source type: Reference]

.Comparisons with correlation computed with receiver generated PRN code shifted half a pulse width early and half a pulse width late (see section 1.4.2.4 of [22]) are used to estimate adjustment required.^ Using the GPS receiver, players can acquire their current location and display the exact stars that they should be seeing up in the sky.
  • TGS 06: Sony debuts PSP GPS - News at GameSpot 13 January 2010 11:56 UTC www.gamespot.com [Source type: FILTERED WITH BAYES]

^ GPS User Equipment consists of the receivers that use the signal from GPS satellites to compute position, time, and velocity primarily for military users.

^ Once the receiver's rough location is known, an internal mathematical model can be used to estimate and correct for the error.
  • GPS GLOBAL POSITIONING SYSTEM 27 January 2010 23:56 UTC www.speedace.info [Source type: FILTERED WITH BAYES]

.The amount of adjustment required for maximum correlation is used in estimating phase error.^ Once the receiver's approximate location is known, a mathematical model can be used to estimate and compensate for these errors.
  • Global Positioning System! 27 January 2010 23:56 UTC www.kipaddotta.com [Source type: FILTERED WITH BAYES]
  • Global Positioning System (GPS) - History, Facts and Pictures 27 January 2010 23:56 UTC www.aviationexplorer.com [Source type: Reference]

^ The basic requirement for the ease of use of a GPS on land and the correlation of the readings directly to a map require that the GPS be capable of handling the UTM grid system (Universal Transverse Mercator grid).
  • A Practical Guide to GPS -UTM 13 January 2010 11:56 UTC www.dbartlett.com [Source type: FILTERED WITH BAYES]

^ The phase difference error in the normal GPS amounts to between 2 and 3 meters (6 to 10 ft) of ambiguity.
  • Global Positioning System! 27 January 2010 23:56 UTC www.kipaddotta.com [Source type: FILTERED WITH BAYES]

.Received frequency offset from the frequency generated by the receiver provides an estimate of phase rate error.^ To perform this tracking, the receiver observes two quantities, phase error and received frequency offset.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ Received frequency offset from the frequency generated by the receiver provides an estimate of phase rate error.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ However, it is often better than no correction, since ionospheric error is the largest error source for a single-frequency GPS receiver.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

.The command for the frequency generator and any further PRN code shifting required are computed as a function of the phase error and the phase rate error in accordance with the control law used.^ Since the GPS receiver computes its approximate altitude, this error is relatively simple to correct, either by applying a function regression or correlating margin of atmospheric error to ambient pressure using a barometric altimeter.
  • Global Positioning System (GPS) - History, Facts and Pictures 27 January 2010 23:56 UTC www.aviationexplorer.com [Source type: Reference]

^ The ionospheric data are transmitted via satellite in Satellite Based Augmentation Systems such as WAAS, which transmits it on the GPS frequency using a special pseudo-random noise sequence (PRN), so only one receiver and antenna are required.
  • Global Positioning System (GPS) - History, Facts and Pictures 27 January 2010 23:56 UTC www.aviationexplorer.com [Source type: Reference]

^ A measurement of the difference in phase between the received GPS PRN code and the PRN code generated internally in the receiver.
  • Micro Modular Technologies - GPS and Wireless Modules - Support 27 January 2010 23:56 UTC www.micro-modular.com [Source type: Reference]

The Doppler velocity is computed as a function of the frequency offset from the carrier nominal frequency. .The Doppler velocity is the velocity component along the line of sight of the receiver relative to the satellite.^ The orbits are arranged so that at least six satellites are always within line of sight from almost everywhere on Earth's surface.
  • Global Positioning System! 27 January 2010 23:56 UTC www.kipaddotta.com [Source type: FILTERED WITH BAYES]
  • Global Positioning System (GPS) - History, Facts and Pictures 27 January 2010 23:56 UTC www.aviationexplorer.com [Source type: Reference]

^ The capacity to determine relative movement enables a receiver to calculate local velocity and orientation, useful in vessels or observations of the Earth.
  • Global Positioning System! 27 January 2010 23:56 UTC www.kipaddotta.com [Source type: FILTERED WITH BAYES]

^ Line Of Sight Propagation (LOS) - Of an electromagnetic wave, propagation in which the transmission path is a direct straight line from the transmitter to the receiver.
  • Micro Modular Technologies - GPS and Wireless Modules - Support 27 January 2010 23:56 UTC www.micro-modular.com [Source type: Reference]

.As the receiver continues to read successive PRN sequences, it will encounter a sudden change in the phase of the 1,023 bit received PRN signal.^ In order to measure the delay, the satellite repeatedly sends a 1,023 bit long pseudo random sequence; the receiver calculates an identical sequence from a known seed number, and shifts it until the two sequences match.
  • GPS GLOBAL POSITIONING SYSTEM 27 January 2010 23:56 UTC www.speedace.info [Source type: FILTERED WITH BAYES]

^ A measurement of the difference in phase between the received GPS PRN code and the PRN code generated internally in the receiver.
  • Micro Modular Technologies - GPS and Wireless Modules - Support 27 January 2010 23:56 UTC www.micro-modular.com [Source type: Reference]

^ Code phase- A measurement of the difference in phase between the received GPS PRN code and the PRN code generated internally in the receiver.
  • Micro Modular Technologies - GPS and Wireless Modules - Support 27 January 2010 23:56 UTC www.micro-modular.com [Source type: Reference]

.This indicates the beginning of a data bit of the navigation message (see section 1.4.2.5 of [22]).^ The week number is transmitted as a ten-bit field in the C/A and P(Y) navigation messages, and so it becomes zero again every 1,024 weeks (19.6 years).
  • Global Positioning System! 27 January 2010 23:56 UTC www.kipaddotta.com [Source type: FILTERED WITH BAYES]

^ The navigation message contains corrections for these errors and estimates of the accuracy of the atomic clock, however they are based on observations and may not indicate the clock's current state.
  • Global Positioning System (GPS) - History, Facts and Pictures 27 January 2010 23:56 UTC www.aviationexplorer.com [Source type: Reference]

^ The week number is transmitted as a ten- bit field in the C/A and P(Y) navigation messages, and so it becomes zero again every 1,024 weeks (19.6 years).
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

.This enables the receiver to begin reading the 20 millisecond bits of the navigation message.^ This enables the receiver to begin reading the 20 millisecond bits of the navigation message.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ This indicates the beginning of a data bit of the navigation message (see section 1.4.2.5 of ).
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ The week number is transmitted as a ten-bit field in the C/A and P(Y) navigation messages, and so it becomes zero again every 1,024 weeks (19.6 years).
  • Global Positioning System! 27 January 2010 23:56 UTC www.kipaddotta.com [Source type: FILTERED WITH BAYES]

.Each subframe of the navigation frame begins with a Telemetry Word which enables the receiver to detect the beginning of a subframe and determine the receiver clock time at which the navigation subframe begins.^ The first word is the telemetry word which indicates the beginning of a subframe and is used by the receiver to synch with the navigation message.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ Each subframe of the navigation frame begins with a Telemetry Word which enables the receiver to detect the beginning of a subframe and determine the receiver clock time at which the navigation subframe begins.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ The receiver knows the receiver clock time of when the beginning of the next subframe was received from detection of the Telemetry Word thereby enabling computation of the transit time and thus the pseudorange.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

.Also each subframe of the navigation frame is identified by bits in the handover word (HOW) thereby enabling the receiver to determine which subframe (see section 1.4.2.6 of [22] and section 2.5.4 of "Essentials of Satellite Navigation Compendium").^ Also each subframe of the navigation frame is identified by bits in the Handover Word (HOW) thereby enabling the receiver to determine which subframe (see section 1.4.2.6 of and section 2.5.4 of "Essentials of Satellite Navigation Compendium" ).
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ The second word is the HOW or handover word and it contains timing information which enables the receiver to identify the subframe and provides the time the next subframe was sent.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ Each subframe of the navigation frame begins with a Telemetry Word which enables the receiver to detect the beginning of a subframe and determine the receiver clock time at which the navigation subframe begins.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

.There can be a delay of up to 30 seconds before the first estimate of position because of the need to read the ephemeris data before computing the intersections of sphere surfaces.^ There can be a delay of up to 30 seconds before the first estimate of position because of the need to read the epheremis data before computing the intersections of sphere surfaces.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ Because ionospheric delay affects the speed of radio waves differently based on their frequencies, a second frequency band was added to help eliminate this type of error.
  • GPS GLOBAL POSITIONING SYSTEM 27 January 2010 23:56 UTC www.speedace.info [Source type: FILTERED WITH BAYES]

^ The time needed to acquire the ephemeris is becoming a significant element of the delay to first position fix, because, as the hardware becomes more capable, the time to lock onto the satellite signals shrinks, but the ephemeris data requires 30 seconds (worst case) before it is received, due to the low data transmission rate.
  • Global Positioning System! 27 January 2010 23:56 UTC www.kipaddotta.com [Source type: FILTERED WITH BAYES]
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

.After a subframe has been read and interpreted, the time the next subframe was sent can be calculated through the use of the clock correction data and the HOW. The receiver knows the receiver clock time of when the beginning of the next subframe was received from detection of the Telemetry Word thereby enabling computation of the transit time and thus the pseudorange.^ After a subframe has been read and interpreted, the time the next subframe was sent can be calculated through the use of the clock correction data and the HOW word.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ Knowing the indicated time the message was received , the GPS receiver can compute the indicated transit time, .
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ The receiver measures the transit time of each message and computes the distance to each satellite.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

.The receiver is potentially capable of getting a new pseudorange measurement at the beginning of each subframe or every 6 seconds.^ The receiver is potentially capable of getting a new pseudorange measurement at the beginning of each subframe or every 6 seconds.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ Because of this, carrier frequency tracking along with PRN code tracking are used to determine when the received satellite's PRN code begins (see "How a GPS Receiver Gets a Lock" ).
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ The measured pseudoranges from four satellites have already been determined with the receiver's internal clock, and thus have an unknown amount of clock error.
  • Global Positioning System! 27 January 2010 23:56 UTC www.kipaddotta.com [Source type: FILTERED WITH BAYES]

.Then the orbital position data, or ephemeris, from the navigation message is used to calculate precisely where the satellite was at the start of the message.^ Data message- See Navigation Message .
  • Micro Modular Technologies - GPS and Wireless Modules - Support 27 January 2010 23:56 UTC www.micro-modular.com [Source type: Reference]

^ Ephemeris- A data set of precise orbit information for a GPS satellite.
  • Micro Modular Technologies - GPS and Wireless Modules - Support 27 January 2010 23:56 UTC www.micro-modular.com [Source type: Reference]

^ Navigation Message- The message transmitted by each GPS satellite.
  • Micro Modular Technologies - GPS and Wireless Modules - Support 27 January 2010 23:56 UTC www.micro-modular.com [Source type: Reference]

.A more sensitive receiver will potentially acquire the ephemeris data more quickly than a less sensitive receiver, especially in a noisy environment.^ A more-sensitive receiver will potentially acquire the ephemeris data quicker than a less-sensitive receiver, especially in a noisy environment.
  • Global Positioning System! 27 January 2010 23:56 UTC www.kipaddotta.com [Source type: FILTERED WITH BAYES]

^ A more sensitive receiver will potentially acquire the ephemeris data more quickly than a less sensitive receiver, especially in a noisy environment.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ A more-sensitive receiver will potentially acquire the ephemeris data more quickly than a less-sensitive receiver, especially in a noisy environment.
  • Global Positioning System (GPS) - History, Facts and Pictures 27 January 2010 23:56 UTC www.aviationexplorer.com [Source type: Reference]

[47]
.This process is repeated for each satellite to which the receiver is listening.^ This process is repeated for each satellite to which the receiver is listening.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ This process is repeated until correlation is achieved or all 1023 possible cases have been tried (see "How a GPS Receiver Gets a Lock" ).
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ While a minimum of four receiving channels is necessary for parallel processing, the extra ones are used to keep track of whatever satellites are in view and to be ready to replace one of the four being used.
  • A Practical Guide to GPS -UTM 13 January 2010 11:56 UTC www.dbartlett.com [Source type: FILTERED WITH BAYES]

Position calculation advanced

.Before providing a more mathematical description of position calculation, the introductory material on this topics is reviewed.^ Before providing a more mathematical description of position calculation, the introductory material on this topics is reviewed.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ To provide an introductory description of how a GPS receiver works, measurement errors will be ignored in this section.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ A typical GPS receiver calculates its position using the signals from four or more GPS satellites.
  • Global Positioning System (GPS) - History, Facts and Pictures 27 January 2010 23:56 UTC www.aviationexplorer.com [Source type: Reference]

.To describe the basic concept of how a GPS receiver works, the errors are at first ignored.^ To provide an introductory description of how a GPS receiver works, measurement errors will be ignored in this section.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ To describe the basic concept of how a GPS receiver works, the errors are at first ignored.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ This paragraph has described the basic concept of GPS while ignoring errors.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

.Using messages received from four satellites, the GPS receiver is able to determine the satellite positions and time sent.^ Let and denote the true coordinates of GPS receiver position at time, .
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ Knowing the indicated time the message was received , the GPS receiver can compute the indicated transit time, .
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ Using messages received from four satellites, the GPS receiver is able to determine the satellite positions and time sent.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

.The x, y, and z components of position and the time sent are designated as \ \left [x_i, y_i, z_i, t_i\right ] where the subscript i denotes which satellite and has the value 1, 2, 3, or 4. Knowing the indicated time the message was received \ \ tr_i, the GPS receiver can compute the transit time of the message as \ \left (tr_i-t_i\right ) .^ Let and denote the true coordinates of GPS receiver position at time, .
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ Knowing the indicated time the message was received , the GPS receiver can compute the indicated transit time, .
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ Let denote the phase of the carrier of satellite j measured by receiver i at time .
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

.Assuming the message traveled at the speed of light, c, the distance traveled, \ \ p_i can be computed as \ \left (tr_i-t_i\right )c .^ Assuming the message traveled at the speed of light, c , the distance traveled, can be computed as .
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ Assume the message travels at the speed of light , then the pseudorange satisfies the equation, .
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ Because of the very large value of the speed of light , c , the estimated distances from the GPS receiver to the satellites, the pseudoranges, are very sensitive to errors in the GPS receiver clock.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

.Knowing the distance from GPS receiver to a satellite and the position of a satellite implies that the GPS receiver is on the surface of a sphere centered at the position of a satellite.^ Thus we know that the indicated position of the GPS receiver is at or near the intersection of the surfaces of four spheres.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ The correct position of the GPS receiver is the one that is closest to the fourth sphere.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ The correct position of the GPS receiver is also the intersection which is closest to the surface of the sphere corresponding to the fourth satellite.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

.Thus we know that the indicated position of the GPS receiver is at or near the intersection of the surfaces of four spheres.^ Knowing the indicated time the message was received , the GPS receiver can compute the indicated transit time, .
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ Thus we know that the indicated position of the GPS receiver is at or near the intersection of the surfaces of four spheres.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ The correct position of the GPS receiver is the one that is closest to the fourth sphere.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

.In the ideal case of no errors, the GPS receiver will be at an intersection of the surfaces of four spheres.^ Once the location and distance of each satellite is known, the receiver should theoretically be located at the intersection of four imaginary spheres, one around each satellite, with a radius equal to the time delay between the satellite and the receiver multiplied by the speed of the radio signals.
  • GPS GLOBAL POSITIONING SYSTEM 27 January 2010 23:56 UTC www.speedace.info [Source type: FILTERED WITH BAYES]

^ We assumed a Gaussian error distribution for measurements of latitude and longitude, which has been shown to be reasonably representative of coordinate measurements based on stand-alone GPS receivers [ 66 ].
  • International Journal of Health Geographics | Full text | Development of a wearable global positioning system for place and health research 27 January 2010 23:56 UTC www.ij-healthgeographics.com [Source type: Academic]

^ Knowing the position and the distance of a satellite indicates that the receiver is located somewhere on the surface of an imaginary sphere centered on that satellite and whose radius is the distance to it.
  • Global Positioning System (GPS) - History, Facts and Pictures 27 January 2010 23:56 UTC www.aviationexplorer.com [Source type: Reference]

.The surfaces of two spheres if they intersect in more than one point intersect in a circle.^ Two sphere surfaces intersecting in a circle The article, trilateration , shows mathematically that two spheres intersecting in more than one point intersect in a circle.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ The distance between these two points is the diameter of the circle of intersection.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ A circle and sphere surface in most cases of practical interest intersect at two points, although it is conceivable that they could intersect in 0 or 1 point.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

.We are here excluding the unrealistic case for GPS purposes of two coincident spheres.^ We are here excluding the unrealistic case for GPS purposes of two coincident spheres.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ We are here excluding the unrealistic case for GPS purposes of three colinear (lying on same straight line) sphere centers.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ Pretty, but your GPS will fall out of this case Rating:1 out of 5 stars I own two Garmin Nuvi’s a 670 and 765.
  • Garmin 3.5Inch Carrying Case | Ultra Gps 16 January 2010 16:26 UTC ultra-gps.com [Source type: FILTERED WITH BAYES]

.A figure, Two Sphere Surfaces Intersecting in a Circle, is shown below depicting this which hopefully will aid the reader in visualizing this intersection.^ Another figure, Surface of Sphere Intersecting a Circle (not disk) at Two Points, is shown below to aid in visualizing this intersection.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ This should make it clear to the reader that the surfaces of the two spheres actually do intersect in a circle.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ A figure, Two Sphere Surfaces Intersecting in a Circle, is shown below depicting this which hopefully will aid the reader in visualizing this intersection.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

.Two points at which the surfaces of the spheres intersect are clearly marked on the figure.^ It is clearly shown in trilateration that the surfaces of three spheres intersect in 0, 1, or 2 points.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ The surfaces of two spheres, if they intersect in more than one point, intersect in a circle.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ Two points at which the surfaces of the spheres intersect are clearly marked on the figure.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

.The distance between these two points is the diameter of the circle of intersection.^ The distance between these two points is the diameter of the circle of intersection.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ You are at either of the two points where the two arcs or circles intersect, but which one?
  • A Practical Guide to GPS -UTM 13 January 2010 11:56 UTC www.dbartlett.com [Source type: FILTERED WITH BAYES]

^ Another figure, Surface of Sphere Intersecting a Circle (not disk) at Two Points, is shown below to aid in visualizing this intersection.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

.If you are not convinced of this, consider how a side view of the intersecting spheres would look.^ If you are not convinced of this, consider how a side view of the intersecting spheres would look.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ And in fact a view from any horizontal direction would look exactly the same.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ Two sphere surfaces intersecting in a circle The article, trilateration , shows mathematically how the equation for a circle is determined.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

.This view would look exactly the same as the figure because of the symmetry of the spheres.^ And in fact a view from any horizontal direction would look exactly the same.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ This view would look exactly the same as the figure because of the symmetry of the spheres.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ If you are not convinced of this, consider how a side view of the intersecting spheres would look.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

.And in fact a view from any horizontal direction would look exactly the same.^ And in fact a view from any horizontal direction would look exactly the same.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ This view would look exactly the same as the figure because of the symmetry of the spheres.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ If you are not convinced of this, consider how a side view of the intersecting spheres would look.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

.This should make it clear to the reader that the surfaces of the two spheres actually do intersect in a circle.^ The surfaces of two spheres, if they intersect in more than one point, intersect in a circle.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ Two points at which the surfaces of the spheres intersect are clearly marked on the figure.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ Another figure, Surface of Sphere Intersecting a Circle (not disk) at Two Points , shows this intersection.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

Two sphere surfaces intersecting in a circle
.The article, trilateration, shows mathematically how the equation for this circle of intersection is determined.^ Again trilateration clearly shows this mathematically.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ Two sphere surfaces intersecting in a circle The article, trilateration , shows mathematically how the equation for a circle is determined.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ Two sphere surfaces intersecting in a circle The article, trilateration , shows mathematically that two spheres intersecting in more than one point intersect in a circle.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

.A circle and sphere surface in most cases of practical interest intersect at two points, although it is conceivable that they could intersect in 0 or 1 point.^ The distance between these two points is the diameter of the circle of intersection.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ A circle and sphere surface in most cases of practical interest intersect at two points, although it is conceivable that they could intersect in 0 or 1 point.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ It is clearly shown in trilateration that the surfaces of three spheres intersect in 0, 1, or 2 points.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

.We are here excluding the unrealistic case for GPS purposes of three colinear (lying on same straight line) sphere centers.^ We are here excluding the unrealistic case for GPS purposes of two coincident spheres.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ We are here excluding the unrealistic case for GPS purposes of three colinear (lying on same straight line) sphere centers.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ In the ideal case of no errors, the GPS receiver will be at an intersection of the surfaces of four spheres.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

.Another figure, Surface of Sphere Intersecting a Circle (not disk) at Two Points, is shown below to aid in visualizing this intersection.^ Another figure, Surface of Sphere Intersecting a Circle (not disk) at Two Points, is shown below to aid in visualizing this intersection.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ The surfaces of two spheres, if they intersect in more than one point, intersect in a circle.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ Another figure, Surface of Sphere Intersecting a Circle (not disk) at Two Points , shows this intersection.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

.Again trilateration clearly shows this mathematically.^ Again trilateration clearly shows this mathematically.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ Two sphere surfaces intersecting in a circle The article, trilateration , shows mathematically that two spheres intersecting in more than one point intersect in a circle.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ Two sphere surfaces intersecting in a circle The article, trilateration , shows mathematically how the equation for a circle is determined.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

.The correct position of the GPS receiver is the one that is closest to the fourth sphere.^ The correct position of the GPS receiver is the one that is closest to the fourth sphere.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ The correct position of the GPS receiver is also the intersection which is closest to the surface of the sphere corresponding to the fourth satellite.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ Correcting a GPS receiver's clock .
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

.This paragraph has described the basic concept of GPS while ignoring errors.^ To describe the basic concept of how a GPS receiver works, the errors are at first ignored.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ This paragraph has described the basic concept of GPS while ignoring errors.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ Basic concept of GPS .
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

.The next problem is how to process the messages when errors are present.^ The next problem is how to process the messages when errors are present.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

Surface of a sphere intersecting a circle (i.e., the edge of a disk) at two points
.Let \ \ b denote the clock error or bias, the amount by which the receiver's clock is slow.^ Let denote the time error, the true time minus the receiver indicated time.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ Let denote the unknown clock error or bias, the amount by which the receiver's clock is slow.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ Surface of a sphere intersecting a circle (i.e., the edge of a disk) at two points Let denote the clock error or bias, the amount by which the receiver's clock is slow.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

.The GPS receiver has four unknowns, the three components of GPS receiver position and the clock bias \ \left [x, y, z, b\right ].^ GPS receiver clock can be advanced if is positive or delayed if is negative.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ The GPS receiver has four unknowns, the three components of GPS receiver position and the clock bias .
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ Correcting a GPS receiver's clock .
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

The equation of the sphere surfaces are given by:
(x-x_i)^2 + (y-y_i)^2 + (z-z_i)^2 = \bigl([tr_i + b - t_i]c\bigr)^2,\;i=1,2,3,4
.Another useful form of these equations is in terms of the pseudoranges, which are simply the ranges approximated based on GPS receiver clock's indicated (i.e., uncorrected) time so that  p_i = \left (tr_i - t_i \right )c.^ Knowing the indicated time the message was received , the GPS receiver can compute the indicated transit time, .
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ Another useful form of these equations is in terms of the pseudoranges , which are simply the ranges approximated based on GPS receiver clock's indicated (i.e.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ Correcting a GPS receiver's clock .
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

Then the equations becomes:
p_i = \sqrt{(x-x_i)^2 + (y-y_i)^2 + (z-z_i)^2}- bc, \;i=1,2,3,4.
.Two of the most important methods of computing GPS receiver position and clock bias are (1) trilateration followed by one dimensional numerical root finding and (2) multidimensional Newton-Raphson calculations.^ The GPS receiver's reported position coordinates.
  • Micro Modular Technologies - GPS and Wireless Modules - Support 27 January 2010 23:56 UTC www.micro-modular.com [Source type: Reference]

^ Accurate measurement of the relative positions of two receivers tracking the same GPS signals.
  • Micro Modular Technologies - GPS and Wireless Modules - Support 27 January 2010 23:56 UTC www.micro-modular.com [Source type: Reference]

^ Ground Track- The plot of positions reported over time by a navigation device such as a GPS receiver.
  • Micro Modular Technologies - GPS and Wireless Modules - Support 27 January 2010 23:56 UTC www.micro-modular.com [Source type: Reference]

.These two methods along with their advantages are discussed.^ These two methods along with their advantages are discussed.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

.
  • The receiver can solve by trilateration followed by one dimensional numerical root finding.^ One advantage of this method is that it involves one dimensional as opposed to multidimensional numerical root finding.
    • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

    ^ The receiver can solve by trilateration followed by one dimensional numerical root finding.
    • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

    ^ Two of the most important methods of computing GPS receiver position and clock bias are (1) trilateration followed by one dimensional numerical root finding and (2) multidimensional Newton-Raphson calculations.
    • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

    [48] .This method involves using trilateration to determine the intersection of the surfaces of three spheres.^ It is clearly shown in trilateration that the surfaces of three spheres intersect in 0, 1, or 2 points.
    • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

    ^ This method involves using Trilateration to determine the intersection of the surfaces of three spheres.
    • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

    ^ It is very unlikely that the surface of the sphere corresponding to the fourth satellite will intersect either of the two points of intersection of the first three since any clock error could cause it to miss intersecting a point.
    • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

    .It is clearly shown in trilateration that the surfaces of three spheres intersect in 0, 1, or 2 points.^ It is clearly shown in trilateration that the surfaces of three spheres intersect in 0, 1, or 2 points.
    • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

    ^ Two points at which the surfaces of the spheres intersect are clearly marked on the figure.
    • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

    ^ A figure, Two Sphere Surfaces Intersecting in a Circle , is shown below.
    • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

    .In the usual case of two intersections, the solution which is nearest the surface of the sphere corresponding to the fourth satellite is chosen.^ The correct position of the GPS receiver is also the intersection which is closest to the surface of the sphere corresponding to the fourth satellite.
    • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

    ^ Two points at which the surfaces of the spheres intersect are clearly marked on the figure.
    • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

    ^ The bias, is then computed based on the distance from the solution to the surface of the sphere corresponding to the fourth satellite.
    • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

    .The surface of the earth can also sometimes be used instead, especially in the case of civilian GPS receivers since it is illegal in the United States to track vehicles of more than 60,000 feet (18,000 m) in altitude.^ The surface of the earth can also sometimes be used instead, especially in the case of civilian GPS receivers since it is illegal in the United States to track vehicles of more than 60,000 feet in altitude.
    • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

    ^ GPS tours are also an example of civilian use.
    • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

    ^ A GPS receiver which can simultaneously track more than one satellite signal.
    • Micro Modular Technologies - GPS and Wireless Modules - Support 27 January 2010 23:56 UTC www.micro-modular.com [Source type: Reference]

    .The bias, \ b is then computed as a function of the distance from the solution to the surface of the sphere corresponding to the fourth satellite.^ The bias, is then computed based on the distance from the solution to the surface of the sphere corresponding to the fourth satellite.
    • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

    ^ Note that is the distance from the computed GPS receiver position to the surface of the sphere corresponding to the fourth satellite.
    • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

    ^ In the usual case of two intersections, the solution which is nearest the surface of the sphere corresponding to the fourth satellite is chosen.
    • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

    .To determine what function to use for computing \ b see the chapter on root finding in [48] or the preview.^ Because of this, carrier frequency tracking along with PRN code tracking are used to determine when the received satellite's PRN code begins (see "How a GPS Receiver Gets a Lock" ).
    • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

    ^ The command for the frequency generator and any further PRN code shifting required are computed as a function of the phase error and the phase rate error in accordance with the control law used.
    • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

    ^ For example if the position of receiver 1 is known but the position of receiver 2 unknown, it may be possible to estimate the position of receiver 2 using numerical root finding and least squares .
    • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

    .Using an updated received time based on this bias, new spheres are computed and the process is repeated.^ Using an updated received time based on this bias, new spheres are computed and the process is repeated.
    • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

    ^ This process is repeated for each satellite to which the receiver is listening.
    • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

    ^ Doppler Aiding- A signal processing strategy that uses a measured doppler shift to help the receiver smoothly track the GPS signal.
    • Micro Modular Technologies - GPS and Wireless Modules - Support 27 January 2010 23:56 UTC www.micro-modular.com [Source type: Reference]

    .This repetition is continued until the distance from the valid trilateration solution is sufficiently close to the surface of the sphere corresponding to the fourth satellite.^ This repetition is continued until the distance from the valid trilateration solution is sufficiently close to the surface of the sphere corresponding to the fourth satellite.
    • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

    ^ A solution will have been found when is zero or sufficiently close to zero for .
    • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

    ^ The bias, is then computed based on the distance from the solution to the surface of the sphere corresponding to the fourth satellite.
    • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

    .One advantage of this method is that it involves one dimensional as opposed to multidimensional numerical root finding.
  • The receiver can utilize a multidimensional root finding method such as the Newton-Raphson method.^ One advantage of this method is that it involves one dimensional as opposed to multidimensional numerical root finding.
    • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

    ^ The receiver can solve by trilateration followed by one dimensional numerical root finding.
    • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

    ^ Two of the most important methods of computing GPS receiver position and clock bias are (1) trilateration followed by one dimensional numerical root finding and (2) multidimensional Newton-Raphson calculations.
    • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

    [48] .Linearize around an approximate solution, say \ \left [x^{(k)}, y^{(k)}, z^{(k)}, b^{(k)}\right ] from iteration k, then solve four linear equations derived from the quadratic equations above to obtain \left [x^{(k+1)}, y^{(k+1)}, z^{(k+1)}, b^{(k+1)}\right ].^ Linearize around an approximate solution, say from iteration k, then solve four linear equations derived from the quadratic equations above to obtain .
    • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

    ^ In order to linearize equation 2, the partial derivatives are computed as .
    • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

    ^ Equations 6 provide a set of four linear equations in four unknowns, the delta terms.
    • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

    .The radii are large and so the sphere surfaces are close to flat.^ The radii are large and so the sphere surfaces are close to flat.
    • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

    ^ It is likely the surfaces of the three spheres intersect since the circle of intersection of the first two spheres is normally quite large and thus the third sphere surface is likely to intersect this large circle.
    • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

    ^ This repetition is continued until the distance from the valid trilateration solution is sufficiently close to the surface of the sphere corresponding to the fourth satellite.
    • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

    [49][50] .This near flatness may cause the iterative procedure to converge rapidly in the case where \ b is near the correct value and the primary change is in the values of  x, y,\; and\; z, since in this case the problem is merely to find the intersection of nearly flat surfaces and thus close to a linear problem.^ The near-Earth intersection will be the correct position for the case of a near-Earth vehicle.
    • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

    ^ This near flatness may cause the iterative procedure to converge rapidly in the case where is near the correct value and the primary change is in the values of , since in this case the problem is merely to find the intersection of nearly flat surfaces and thus close to a linear problem.
    • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

    ^ The radii are large and so the sphere surfaces are close to flat.
    • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

    .However when \ b is changing significantly, this near flatness does not appear to be advantageous in producing rapid convergence, since in this case these near flat surfaces will be moving as the spheres expand and contract.^ However when is changing significantly, this near flatness does not appear to be advantageous in producing rapid convergence, since in this case these near flat surfaces will be moving as the spheres expand and contract.
    • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

    ^ The radii are large and so the sphere surfaces are close to flat.
    • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

    ^ It is likely the surfaces of the three spheres intersect since the circle of intersection of the first two spheres is normally quite large and thus the third sphere surface is likely to intersect this large circle.
    • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

    .This possible fast convergence is an advantage of this method.^ This possible fast convergence is an advantage of this method.
    • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

    .Also it has been claimed that this method is the "typical" method used by GPS receivers.^ Also it has been claimed that this method is the "typical" method used by GPS receivers.
    • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

    ^ A typical GPS receiver with integrated antenna.
    • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

    ^ Artillery projectiles with embedded GPS receivers able to withstand accelerations of 12,000 G have been developed for use in 155 mm howitzers .
    • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

    [51][52][53] A disadvantage of this multidimensional root finding method as compared to single dimensional root findiing is that according to,[48] "There are no good general methods for solving systems of more than one nonlinear equations." For a more detailed description of the mathematics see Multidimensional Newton Raphson.
  • Other methods include:
  1. Solving for the intersection of the expanding signals from light cones in 4-space cones
  2. Solving for the intersection of hyperboloids determined by the time difference of signals received from satellites utilizing multilateration,
  3. Solving the equations in accordance with .[51][52][54]
  4. .
  • When more than four satellites are available, a decision must be made on whether to use the four best or more than four taking into considerations such factors as number of channels, processing capability, and geometric dilution of precision.^ When more than four satellites are available, a decision must be made on whether to use the four best or more than four taking into considerations such factors as number of channels, processing capability, and geometric dilution of precision .
    • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

    ^ Geometric dilution of precision computation (DOP) .
    • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

    ^ Therefore d as in dilution of precision is used.
    • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

    .Using more than four results in an over-determined system of equations with no unique solution, which must be solved by least-squares or a similar technique.^ To get estimates for an over determined system, least squares can be used.
    • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

    ^ Using more than four results in an over-determined system of equations with no unique solution, which must be solved by least-squares or a similar technique.
    • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

    ^ Using the values of and determined by this linear equation solution, .
    • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

    .If all visible satellites are used, the results are always at least as good as using the four best, and usually better.^ If all visible satellites are used, the results are always at least as good as using the four best, and usually better.
    • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

    ^ The orbits are designed so at least four satellites are always within line of sight from almost any place on earth.
    • GPS GLOBAL POSITIONING SYSTEM 27 January 2010 23:56 UTC www.speedace.info [Source type: FILTERED WITH BAYES]

    ^ While a minimum of four receiving channels is necessary for parallel processing, the extra ones are used to keep track of whatever satellites are in view and to be ready to replace one of the four being used.
    • A Practical Guide to GPS -UTM 13 January 2010 11:56 UTC www.dbartlett.com [Source type: FILTERED WITH BAYES]

    Also the errors in results can be estimated through the residuals.[55] .With each combination of four or more satellites, a geometric dilution of precision (GDOP) factor can be calculated, based on the relative sky directions of the satellites used.^ Geometric dilution of precision computation (DOP) .
    • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

    ^ Therefore d as in dilution of precision is used.
    • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

    ^ With each combination of four or more satellites, a geometric dilution of precision (GDOP) vector can be calculated, based on the relative sky positions of the satellites used.As more satellites are picked up, pseudoranges from more combinations of four satellites can be processed to add more estimates to the location and clock offset.
    • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

    [55][56] .As more satellites are picked up, pseudoranges from more combinations of four satellites can be processed to add more estimates to the location and clock offset.^ With each combination of four or more satellites, a geometric dilution of precision (GDOP) vector can be calculated, based on the relative sky positions of the satellites used.As more satellites are picked up, pseudoranges from more combinations of four satellites can be processed to add more estimates to the location and clock offset.
    • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

    ^ Pseudorange differs from the actual range by the amount that the satellite and receiver clocks are offset, by propagation delays, and other errors including those introduced by selective availability.
    • Micro Modular Technologies - GPS and Wireless Modules - Support 27 January 2010 23:56 UTC www.micro-modular.com [Source type: Reference]

    ^ The master control station, at Schriever AFB, processes their combined observations and sends updates to the satellites through the stations at Ascension Island, Diego Garcia, Kwajalein.
    • GPS GLOBAL POSITIONING SYSTEM 27 January 2010 23:56 UTC www.speedace.info [Source type: FILTERED WITH BAYES]

    .The receiver then determines which combinations to use and how to calculate the estimated position by determining the weighted average of these positions and clock offsets.^ Geometric trilateration is used to combine these distances with the location of the satellites to determine the receiver's location.
    • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

    ^ The receiver then determines which combinations to use and how to calculate the estimated position by determining the weighted average of these positions and clock offsets.
    • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

    ^ With each combination of four or more satellites, a geometric dilution of precision (GDOP) vector can be calculated, based on the relative sky positions of the satellites used.As more satellites are picked up, pseudoranges from more combinations of four satellites can be processed to add more estimates to the location and clock offset.
    • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

    .After the final location and time are calculated, the location is expressed in a specific coordinate system such as latitude and longitude, using the WGS 84 geodetic datum or a local system specific to a country.^ Position- A location described by coordinates (typically Latitude Longitude and Altitude).
    • Micro Modular Technologies - GPS and Wireless Modules - Support 27 January 2010 23:56 UTC www.micro-modular.com [Source type: Reference]

    ^ The GPS system normally uses WGS-84 .
    • Micro Modular Technologies - GPS and Wireless Modules - Support 27 January 2010 23:56 UTC www.micro-modular.com [Source type: Reference]

    ^ After the final location and time are calculated, the location is expressed in a specific coordinate system such as latitude and longitude , using the WGS 84 geodetic datum or a local system specific to a country.
    • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

    [57]
  • .
  • Finally, results from other positioning systems such as GLONASS or the upcoming Galileo can be used in the fit, or used to double check the result.^ Finally, results from other positioning systems such as GLONASS or the upcoming Galileo can be used in the fit, or used to double check the result.
    • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

    ^ L3 (1381.05 MHz): Used by the Nuclear Detonation (NUDET) Detection System Payload (NDS) to signal detection of nuclear detonations and other high-energy infrared events.
    • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

    ^ To use such a numerical method, an initial approximation of the position of receiver 2 is required.
    • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

    .(By design, these systems use the same bands, so much of the receiver circuitry can be shared, though the decoding is different.^ (By design, these systems use the same bands, so much of the receiver circuitry can be shared, though the decoding is different.
    • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

    ^ These receivers provide real-time situational awareness for the warfighter much more quickly and accurately than previous, conventional methods.

    ^ Geometric trilateration is used to combine these distances with the location of the satellites to determine the receiver's location.
    • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

    )
Multidimensional Newton-Raphson for GPS
. This section provides a more detailed discussion of the equations used in the second method described in Position calculation advanced.^ Position calculation advanced .
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ In the same method is discussed but the equations are not shown.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ This section provides a more detailed discussion of the equations used in the second method described in Position calculation advanced .
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

.The linearized equations are developed using the appropriate partial derivatives and the algorithm is described.^ In order to linearize equation 2, the partial derivatives are computed as .
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ The linearized equations are developed using the appropriate partial derivatives and the algorithm is described.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ This section describes the derivation of these equations.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

.In [50] the same method is discussed but the equations are not shown.^ In the same method is discussed but the equations are not shown.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ This section provides a more detailed discussion of the equations used in the second method described in Position calculation advanced .
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

.Let  x, y\; and  z\; denote the true coordinates of GPS receiver position at time, \ t.^ Let and denote the true coordinates of GPS receiver position at time, .
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ Let denote the phase of the carrier of satellite j measured by receiver i at time .
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ Let denote the time error, the true time minus the receiver indicated time.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

.Let \ b denote the unknown clock error or bias, the amount by which the receiver's clock is slow.^ Let denote the time error, the true time minus the receiver indicated time.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ Let denote the unknown clock error or bias, the amount by which the receiver's clock is slow.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ Surface of a sphere intersecting a circle (i.e., the edge of a disk) at two points Let denote the clock error or bias, the amount by which the receiver's clock is slow.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

.Let the coordinates of each satellite, and the time the message was sent, be  \left [x_i, y_i, z_i, t_i\right ], let the GPS clock's indicated received time be  tr_i\; \mbox{for} \ i=1,2,3,4 and c be the speed of light.^ Let and denote the true coordinates of GPS receiver position at time, .
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ Knowing the indicated time the message was received , the GPS receiver can compute the indicated transit time, .
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ Let denote the phase of the carrier of satellite j measured by receiver i at time .
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

The pseudorange is computed as:
p_i = \left(tr_i - t_i\right)c
Assume the message travels at the speed of light, then the pseudorange satisfies the equation:
p_i = \sqrt{(x-x_i)^2 + (y-y_i)^2 + (z-z_i)^2}- bc, \;\;\mbox{for} \; i=1,2,3,4. \qquad (1)
.When an approximate solution,  \left [x^{(k)}, y^{(k)}, z^{(k)}, b^{(k)}\right ] rather than the exact solution,  \left [x, y, z, b\right ] is used in equation 1, there is a residual,  f_i^{(k)}.^ When an approximate solution, rather than the exact solution, is used in equation 1, there is a residual, .
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ Linearize around an approximate solution, say from iteration k, then solve four linear equations derived from the quadratic equations above to obtain .
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ Another useful form of these equations is in terms of the pseudoranges , which are simply the ranges approximated based on GPS receiver clock's indicated (i.e.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

Transforming \ p_i to the right hand side of the equation there results,
f_i^{(k)} = \sqrt{(x^{(k)}-x_i)^2 + (y^{(k)}-y_i)^2 + (z^{(k)}-z_i)^2}- b^{(k)}c - p_i, \;\;
\mbox{for} \; i=1,2,3,4. \qquad \qquad \qquad \qquad \qquad \qquad \qquad \qquad \qquad \qquad \;\;\;\;\; (2)
.A solution will have been found when  f_i^{(k)} is zero or sufficiently close to zero for \ i=1,2,3,4.^ A solution will have been found when is zero or sufficiently close to zero for .
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ This repetition is continued until the distance from the valid trilateration solution is sufficiently close to the surface of the sphere corresponding to the fourth satellite.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

In order to linearize equation 2, the partial derivatives are computed as:
\frac{\partial f_i^{(k)}} {\partial x^{(k)}} = \frac {(x^{(k)} - x_i)} {R_i^{(k)} }, \frac{\partial f_i^{(k)}} {\partial y^{(k)}} = \frac {(y^{(k)}-y_i)} {R_i^{(k)}},
\frac{\partial f_i^{(k)}} {\partial z^{(k)}} = \frac {(z^{(k)} -z_i)} {R_i^{(k)} }, \frac{\partial f_i^{(k)}} {\partial b^{(k)}} = -c \qquad \qquad \qquad \qquad \qquad \qquad \qquad \;\;\;(3)
where
R_i^{(k)} = \sqrt{(x^{(k)}-x_i)^2 + (y^{(k)}-y_i)^2 + (z^{(k)}-z_i)^2}.
Linearizing the right hand side of equation 2 about the approximate solution,  \left [x^{(k)}, y^{(k)}, z^{(k)}, b^{(k)}\right ] there results
f_i^{(k)} = \frac {(x^{(k)}-x_i)} {R_i^{(k)}} x^{(k)} + \frac {(y^{(k)}-y_i)} {R_i^{(k)}} y^{(k)} + \frac {(z^{(k)}-z_i)} {R_i^{(k)}} z^{(k)} - b^{(k)}c - p_i + \epsilon_i, \;\;
\mbox{for} i=1,2,3,4 \qquad \qquad \qquad \qquad \qquad \qquad \qquad \qquad \qquad \qquad \qquad(4)
where .\ \epsilon_i is the residual due to linearization which is in addition to the residual, \ f_i^{(k)} , due to an approximate solution.^ Linearize around an approximate solution, say from iteration k, then solve four linear equations derived from the quadratic equations above to obtain .
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ When an approximate solution, rather than the exact solution, is used in equation 1, there is a residual, .
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ Linearizing the right hand side of equation 2 about the approximate solution, there results .
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

In order to drive \ f_i^{(k+1)} closer to zero choose the values  \left [x^{(k+1)}, y^{(k+1)}, z^{(k+1)}, b^{(k+1)}\right ] such that
-f_i^{(k)} = \frac {(x^{(k)}-x_i)} {p_i} (x^{(k+1)}- x^{(k)}) + \frac {(y^{(k)}-y_i)} {p_i} (y^{(k+1)}- y^{(k)})\;+
\frac {(z^{(k)}-z_i)} {p_i} (z^{(k+1)}- z^{(k)}) - (b^{(k+1)} - b^{(k)})c - p_i. \qquad \qquad \qquad \qquad (5)
That is choose the values
\left [x^{(k+1)}, y^{(k+1)}, z^{(k+1)}, b^{(k+1)}\right ]
such that the residual in equation 2 changes by approximately \ \ - f_i^{(k)}.
Let
\Delta x^{(k+1)}\ =\ (x^{(k+1)}- x^{(k)}), \Delta y^{(k+1)}\ =\ (y^{(k+1)}- y^{(k)}),
\Delta z^{(k+1)}\ =\ (z^{(k+1)}- z^{(k)}), \Delta b^{(k+1)}\ =\ (b^{(k+1)}- b^{(k)}).
Substituting and transposing \ \ p_i to the left hand side of the equation, there results
- f_i^{(k)} + p_i = \frac {(x^{(k)}-x_i)} {p_i} \Delta x^{(k+1)} + \frac {(y^{(k)}-y_i)} {p_i} \Delta y^{(k+1)} \;+
\frac {(z^{(k)}-z_i)} {p_i} \Delta z^{(k+1)} - \Delta b^{(k+1)} c. \qquad \qquad \qquad \qquad \qquad \qquad \qquad \;\;\;\;\;\;(6)
Equations 6 provide a set of four linear equations in four unknowns, the delta terms. .They are in a form for solution.^ They are in a form for solution.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

Using the values of \ \;\Delta x^{(k+1)}, \Delta y^{(k+1)}, \Delta z^{(k+1)} and \; \Delta b^{(k+1)} determined by this linear equation solution,
\left [x^{(k+1)}, y^{(k+1)}, z^{(k+1)}, b^{(k+1)}\right ]
is evaluated using:
\ x^{(k+1)}\ =\ x^{(k)}\ +\Delta x^{(k+1)}, \ y^{(k+1)}\ =\ y^{(k)}\ +\Delta y^{(k+1)},
\ z^{(k+1)}\ =\ z^{(k)}\ +\Delta z^{(k+1)}, \ b^{(k+1)}\ =\ b^{(k)}\ +\Delta b^{(k+1)}. \qquad \qquad \;\;\;\;\;\; (7)
Then set \ k = k + 1 in equations 2 through 6, plug the terms
\left \{ x^{(k+1)}, y^{(k+1)}, z^{(k+1)}, b^{(k+1)} \right \}
from equations .7 into equations 2, set  \ k = k + 1 in equations 7, and reevaluate the residuals in equations 2. This procedure is repeated until the residuals are sufficiently small in magnitude.^ This procedure is repeated until the residuals are sufficiently small in magnitude.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ This may require the use of a numerical procedure such as one of those found in the chapter on root finding and nonlinear sets of equations in Numerical Recipes.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

P(Y) code

.Calculating a position with the P(Y) signal is generally similar in concept, assuming one can decrypt it.^ Calculating a position with the P(Y) signal is generally similar in concept, assuming one can decrypt it.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ Differential-enabled GPS receivers can receive the broadcast DGPS signals from the ground stations and make correction calculations, improving accuracy of position to within 3 m or less.
  • International Journal of Health Geographics | Full text | Development of a wearable global positioning system for place and health research 27 January 2010 23:56 UTC www.ij-healthgeographics.com [Source type: Academic]

^ If correlation is not achieved, the 1023 bits of the receiver's internally generated PRN code are shifted by one bit relative to the satellite's PRN code and the signals are again compared.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

.The encryption is essentially a safety mechanism: if a signal can be successfully decrypted, it is reasonable to assume it is a real signal being sent by a GPS satellite.^ The encryption is essentially a safety mechanism: if a signal can be successfully decrypted, it is reasonable to assume it is a real signal being sent by a GPS satellite .
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ The GPS satellites continuously transmit digital radio signals that contain data on the satellites location and the exact time to the earth-bound receivers.

^ The windshield on some cars has a metallic coating through which the GPS can't receive the weak signals from the satellites.
  • A Practical Guide to GPS -UTM 13 January 2010 11:56 UTC www.dbartlett.com [Source type: FILTERED WITH BAYES]

.September 2007" style="white-space:nowrap;">[citation needed] In comparison, civil receivers are highly vulnerable to spoofing since correctly formatted C/A signals can be generated using readily available signal generators.^ In comparison, civil receivers are highly vulnerable to spoofing since correctly formatted C/A signals can be generated using readily available signal generators.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ In fact, the system serves millions of civil users with over a 1.4 million handheld and vehicle-mounted GPS receivers having been produced each year since 1997.

^ Doppler Aiding- A signal processing strategy that uses a measured doppler shift to help the receiver smoothly track the GPS signal.
  • Micro Modular Technologies - GPS and Wireless Modules - Support 27 January 2010 23:56 UTC www.micro-modular.com [Source type: Reference]

.RAIM features do not protect against spoofing, since RAIM only checks the signals from a navigational perspective.^ RAIM features do not protect against spoofing, since RAIM only checks the signals from a navigational perspective.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ It fits well, but the case is really only designed to protect against scratches and dings of the LCD instead of the device itself.
  • Garmin 3.5Inch Carrying Case | Ultra Gps 16 January 2010 16:26 UTC ultra-gps.com [Source type: FILTERED WITH BAYES]

^ In comparison, civil receivers are highly vulnerable to spoofing since correctly formatted C/A signals can be generated using readily available signal generators.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

Error sources and analysis

Sources of User Equivalent Range Errors (UERE)
Source Effect (m)
Signal arrival C/A ±3
Signal arrival P(Y) ±0.3
Ionospheric effects ±5
Ephemeris errors ±2.5
Satellite clock errors ±2
Multipath distortion ±1
Tropospheric effects ±0.5
\ \sigma_R C/A ±6.7
\ \sigma_R P(Y) ±6.0
Accuracy of Navigation Systems.svg
Error Diagram Showing Relation of Indicated Receiver Position, Intersection of Sphere Surfaces, and True Receiver Position in Terms of Pseudorange Errors, PDOP, and Numerical Errors
.User equivalent range errors (UERE) are shown in the table.^ User equivalent range errors (UERE) are shown in the table.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ Error Diagram Showing Relation of Indicated Receiver Position, Intersection of Sphere Surfaces, and True Receiver Position in Terms of Pseudorange Errors, PDOP, and Numerical Errors The term user equivalent range error (UERE) refers to the standard deviation of a component of the error in the distance from receiver to a satellite.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ The standard deviation of the error in receiver position, , is computed by multiplying PDOP (Position Dilution Of Precision) by , the standard deviation of the user equivalent range errors.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

.There is also a numerical error with an estimated value, \ \sigma_{num} , of about 1 meter.^ There is also a numerical error with an estimated value, , of about 1 meter.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ Because of the very large value of the speed of light , c , the estimated distances from the GPS receiver to the satellites, the pseudoranges, are very sensitive to errors in the GPS receiver clock.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ Since GPS signals propagate at the speed of light , this represents an error of about 3 meters.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

.The standard deviations, \ \sigma_R, for the coarse/acquisition and precise codes are also shown in the table.^ The standard deviations, , for the coarse/acquisition and precise codes are also shown in the table.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ The standard deviation of the error in receiver position, , is computed by multiplying PDOP (Position Dilution Of Precision) by , the standard deviation of the user equivalent range errors.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ See Course Deviation Indicator See Code Division Multiple Access See Circular Error Probable A statistical measure of horizontal precision accuracy.
  • Micro Modular Technologies - GPS and Wireless Modules - Support 27 January 2010 23:56 UTC www.micro-modular.com [Source type: Reference]

.These standard deviations are computed by taking the square root of the sum of the squares of the individual components (i.e., RSS for root sum squares).^ These standard deviations are computed by taking the square root of the sum of the squares of the individual components (i.e.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ RSS for root sum squares).
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ The standard deviation of the error in receiver position, , is computed by multiplying PDOP (Position Dilution Of Precision) by , the standard deviation of the user equivalent range errors.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

.To get the standard deviation of receiver position estimate, these range errors must be multiplied by the appropriate dilution of precision terms and then RSS'ed with the numerical error.^ The standard deviation of the error in receiver position, , is computed by multiplying PDOP (Position Dilution Of Precision) by , the standard deviation of the user equivalent range errors.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ Estimated Position Error (EPE) - An estimate of horizontal position error.
  • Micro Modular Technologies - GPS and Wireless Modules - Support 27 January 2010 23:56 UTC www.micro-modular.com [Source type: Reference]

^ An estimate of horizontal position error.
  • Micro Modular Technologies - GPS and Wireless Modules - Support 27 January 2010 23:56 UTC www.micro-modular.com [Source type: Reference]

.Electronics errors are one of several accuracy-degrading effects outlined in the table above.^ Electronics errors are one of several accuracy-degrading effects outlined in the table above.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

.When taken together, autonomous civilian GPS horizontal position fixes are typically accurate to about 15 meters (50 ft).^ When taken together, autonomous civilian GPS horizontal position fixes are typically accurate to about 15 meters (50 ft).
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ Typical horizontal positioning accuracy for military users is 7 to 10 meters.

^ However, the advancement of technology means that today, civilian GPS fixes under a clear view of the sky are on average accurate to about 5 meters (16 ft) horizontally.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

.These effects also reduce the more precise P(Y) code's accuracy.^ These effects also reduce the more precise P(Y) code's accuracy.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ Position precision estimates worsened under urban canyon conditions where multipath effects are expected to be more of an issue.
  • International Journal of Health Geographics | Full text | Development of a wearable global positioning system for place and health research 27 January 2010 23:56 UTC www.ij-healthgeographics.com [Source type: Academic]

^ These traits make precise measurement and compensation of humidity errors more difficult than ionospheric effects.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

.However, the advancement of technology means that today, civilian GPS fixes under a clear view of the sky are on average accurate to about 5 meters (16 ft) horizontally.^ BUT, this technique presupposes that you have ample battery power (external hook-up) AND a clear view of the sky.
  • A Practical Guide to GPS -UTM 13 January 2010 11:56 UTC www.dbartlett.com [Source type: FILTERED WITH BAYES]

^ Figure 5 shows the relationship between horizontal (HDOP) and positional dilution of position (PDOP) under static and dynamic GPS instrument testing conditions.
  • International Journal of Health Geographics | Full text | Development of a wearable global positioning system for place and health research 27 January 2010 23:56 UTC www.ij-healthgeographics.com [Source type: Academic]

^ In more urbanized areas the application of GPS technology to accurately measure location over time requires evaluative pilot testing for reliability and validity to ensure feasibility of the technology under actual conditions.
  • International Journal of Health Geographics | Full text | Development of a wearable global positioning system for place and health research 27 January 2010 23:56 UTC www.ij-healthgeographics.com [Source type: Academic]

(see summary table near end of "Sources of Errors in GPS")
.The term user equivalent range error (UERE) refers to the standard deviation of a component of the error in the distance from receiver to a satellite.^ Error Diagram Showing Relation of Indicated Receiver Position, Intersection of Sphere Surfaces, and True Receiver Position in Terms of Pseudorange Errors, PDOP, and Numerical Errors The term user equivalent range error (UERE) refers to the standard deviation of a component of the error in the distance from receiver to a satellite.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ The standard deviation of the error in receiver position, , is computed by multiplying PDOP (Position Dilution Of Precision) by , the standard deviation of the user equivalent range errors.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ User equivalent range errors (UERE) are shown in the table.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

.The standard deviation of the error in receiver position, \ \sigma_{rc}, is computed by multiplying PDOP (Position Dilution Of Precision) by \ \sigma_R, the standard deviation of the user equivalent range errors.^ The standard deviation of the error in receiver position, , is computed by multiplying PDOP (Position Dilution Of Precision) by , the standard deviation of the user equivalent range errors.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ Geometric dilution of precision computation (DOP) .
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ User equivalent range errors (UERE) are shown in the table.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

.\ \sigma_R is computed by taking the square root of the sum of the squares of the individual component standard deviations.^ These standard deviations are computed by taking the square root of the sum of the squares of the individual components (i.e.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ RSS for root sum squares).
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ The standard deviation of the error in receiver position, , is computed by multiplying PDOP (Position Dilution Of Precision) by , the standard deviation of the user equivalent range errors.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

.PDOP is computed as a function of receiver and satellite positions.^ PDOP is computed as a function of receiver and satellite positions.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ Error Diagram Showing Relation of Indicated Receiver Position, Intersection of Sphere Surfaces, and True Receiver Position in Terms of Pseudorange Errors, PDOP, and Numerical Errors The term user equivalent range error (UERE) refers to the standard deviation of a component of the error in the distance from receiver to a satellite.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ The standard deviation of the error in receiver position, , is computed by multiplying PDOP (Position Dilution Of Precision) by , the standard deviation of the user equivalent range errors.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

.Consider the unit vectors pointing from the receiver to the satellites.^ In addition to the satellites, the system consists of a worldwide satellite control network and GPS receiver units that acquire the satellites signals and translate them into position information.

.Connecting the tails of these unit vectors forms a tetrahedron.^ Connecting the tails of these unit vectors forms a tetrahedron .
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

.PDOP is sometimes approximated as being inversely proportional to the tetrahedron volume.^ PDOP is sometimes approximated as being inversely proportional to the tetrahedron volume [ 31 ] .
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

[50] .A more detailed description of how to calculate PDOP is given in the section, geometric dilution of precision computation (GDOP).^ Geometric dilution of precision computation (DOP) .
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ PDOP, TDOP and GDOP are given by .
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ The equations for computing the geometric dilution of precision terms have been described in the previous section.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

\ \sigma_R for the C/A code is given by:
\sigma_R= \sqrt{3^2+5^2+2.5^2+2^2+1^2+0.5^2} \, meters \,=\,6.7 \, meters
The standard deviation of the error in estimated receiver position \ \sigma_{rc}, again for the C/A code is given by:
\ \sigma_{rc} = \sqrt{PDOP^2 	imes \sigma_R^2 + \sigma_{num}^2} = \sqrt{PDOP^2 	imes 6.7^2 + 1^2} \, meters
.The error diagram to the right shows the inter relationship of indicated receiver position, true receiver position, and the intersection of the four sphere surfaces.^ Thus we know that the indicated position of the GPS receiver is at or near the intersection of the surfaces of four spheres.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ Let denote the time error, the true time minus the receiver indicated time.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ The error diagram to the right shows the inter relationship of indicated receiver position, true receiver position, and the intersection of the four sphere surfaces.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

Signal arrival time measurement

.The position calculated by a GPS receiver requires the current time, the position of the satellite and the measured delay of the received signal.^ GPS receiver clock can be advanced if is positive or delayed if is negative.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ Let and denote the true coordinates of GPS receiver position at time, .
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ Accurate measurement of the relative positions of two receivers tracking the same GPS signals.
  • Micro Modular Technologies - GPS and Wireless Modules - Support 27 January 2010 23:56 UTC www.micro-modular.com [Source type: Reference]

.The position accuracy is primarily dependent on the satellite position and signal delay.^ The position accuracy is primarily dependent on the satellite position and signal delay.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ As expected, signal accuracy for walking and cycling deteriorated as the potential for the built environment to interfere with satellite reception increased.
  • International Journal of Health Geographics | Full text | Development of a wearable global positioning system for place and health research 27 January 2010 23:56 UTC www.ij-healthgeographics.com [Source type: Academic]

^ The antenna has a 2 m cable and can be positioned appropriately to maximize visibility of the sky and satellite signal reception.
  • International Journal of Health Geographics | Full text | Development of a wearable global positioning system for place and health research 27 January 2010 23:56 UTC www.ij-healthgeographics.com [Source type: Academic]

.To measure the delay, the receiver compares the bit sequence received from the satellite with an internally generated version.^ The 1023 bits of the satellite PRN signal are compared with the receiver PRN signal.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ To measure the delay, the receiver compares the bit sequence received from the satellite with an internally generated version.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ A measurement of the difference in phase between the received GPS PRN code and the PRN code generated internally in the receiver.
  • Micro Modular Technologies - GPS and Wireless Modules - Support 27 January 2010 23:56 UTC www.micro-modular.com [Source type: Reference]

.By comparing the rising and trailing edges of the bit transitions, modern electronics can measure signal offset to within about one percent of a bit pulse width, \frac{0.01}{(1.023 	imes 10^6 /sec)}, or approximately 10 nanoseconds for the C/A code.^ By comparing the rising and trailing edges of the bit transitions, modern electronics can measure signal offset to within about one percent of a bit pulse width, , or approximately 10 nanoseconds for the C/A code.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ Assuming the same one percent of bit pulse width accuracy, the high-frequency P(Y) signal results in an accuracy of or about 30 centimeters.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ The Gold codes used in GPS are a sequence of 1023 bits with a period of one millisecond.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

.Since GPS signals propagate at the speed of light, this represents an error of about 3 meters.^ Since GPS signals propagate at the speed of light , this represents an error of about 3 meters.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ However, it is often better than no correction, since ionospheric error is the largest error source for a single-frequency GPS receiver.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ Because of the very large value of the speed of light , c , the estimated distances from the GPS receiver to the satellites, the pseudoranges, are very sensitive to errors in the GPS receiver clock.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

.This component of position accuracy can be improved by a factor of 10 using the higher-chiprate P(Y) signal.^ This component of position accuracy can be improved by a factor of 10 using the higher-chiprate P(Y) signal.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ A signal processing strategy that uses the GPS carrier phase to augment the measured code phase for better accuracy.
  • Micro Modular Technologies - GPS and Wireless Modules - Support 27 January 2010 23:56 UTC www.micro-modular.com [Source type: Reference]

^ GPS is also used to investigate the positional accuracy of geocoding processing in epidemiological research [ 47 , 48 ].
  • International Journal of Health Geographics | Full text | Development of a wearable global positioning system for place and health research 27 January 2010 23:56 UTC www.ij-healthgeographics.com [Source type: Academic]

.Assuming the same one percent of bit pulse width accuracy, the high-frequency P(Y) signal results in an accuracy of \frac {(0.01 	imes 300,000,000\ m/sec)} {(10.23 	imes 10^6 / sec)} or about 30 centimeters.^ Assuming the same one percent of bit pulse width accuracy, the high-frequency P(Y) signal results in an accuracy of or about 30 centimeters.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ If correlation is not achieved, the 1023 bits of the receiver's internally generated PRN code are shifted by one bit relative to the satellite's PRN code and the signals are again compared.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ By eliminating this source of error, CPGPS coupled with DGPS normally realizes between 20 and 30 centimeters (8 to 12 inches) of absolute accuracy.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

Atmospheric effects

.Inconsistencies of atmospheric conditions affect the speed of the GPS signals as they pass through the Earth's atmosphere, especially the ionosphere.^ Variability in atmospheric conditions may affect the velocity of GPS signals.
  • International Journal of Health Geographics | Full text | Development of a wearable global positioning system for place and health research 27 January 2010 23:56 UTC www.ij-healthgeographics.com [Source type: Academic]

^ Inconsistencies of atmospheric conditions affect the speed of the GPS signals as they pass through the Earth's atmosphere , especially the ionosphere .
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ GPS signals can also be affected by multipath issues, where the radio signals reflect off surrounding terrain; buildings, canyon walls, hard ground, etc.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

.Correcting these errors is a significant challenge to improving GPS position accuracy.^ Correcting these errors is a significant challenge to improving GPS position accuracy.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ However, it is often better than no correction, since ionospheric error is the largest error source for a single-frequency GPS receiver.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ GPS is also used to investigate the positional accuracy of geocoding processing in epidemiological research [ 47 , 48 ].
  • International Journal of Health Geographics | Full text | Development of a wearable global positioning system for place and health research 27 January 2010 23:56 UTC www.ij-healthgeographics.com [Source type: Academic]

.These effects are smallest when the satellite is directly overhead and become greater for satellites nearer the horizon since the path through the atmosphere is longer (see airmass).^ These effects are greater for satellite signals nearer the horizon where signals travel further through the atmosphere before reaching the GPS receiver.
  • International Journal of Health Geographics | Full text | Development of a wearable global positioning system for place and health research 27 January 2010 23:56 UTC www.ij-healthgeographics.com [Source type: Academic]

^ The sum of these atmospheric effects can result in errors of 30 to 60 m and vary depending on the angle of inclination of the satellites in view [ 41 ].
  • International Journal of Health Geographics | Full text | Development of a wearable global positioning system for place and health research 27 January 2010 23:56 UTC www.ij-healthgeographics.com [Source type: Academic]

^ See Leg A data set of approximate orbit information, clock corrections, and atmospheric delay parameters for all GPS satellites.
  • Micro Modular Technologies - GPS and Wireless Modules - Support 27 January 2010 23:56 UTC www.micro-modular.com [Source type: Reference]

.Once the receiver's approximate location is known, a mathematical model can be used to estimate and compensate for these errors.^ Once the receiver's approximate location is known, a mathematical model can be used to estimate and compensate for these errors.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ Since the GPS receiver computes its approximate altitude, this error is relatively simple to correct, either by applying a function regression or correlating margin of atmospheric error to ambient pressure using a barometric altimeter.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ To use such a numerical method, an initial approximation of the position of receiver 2 is required.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

.Ionospheric delay of a microwave signal depends on its frequency.^ Because ionospheric delay affects the speed of microwave signals differently depending on their frequency — a characteristic known as dispersion - delays measured on two or more frequency bands can be used to measure dispersion, and this measurement can then be used to estimate the delay at each frequency.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ Then all users will be able to perform dual-frequency measurements and directly compute ionospheric delay errors.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ This effect both is more localized and changes more quickly than ionospheric effects, and is not frequency dependent.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

.This phenomenon is known as dispersion and can be calculated from measurements of delays for two or more frequency bands, allowing delays at other frequencies to be estimated.^ Because ionospheric delay affects the speed of microwave signals differently depending on their frequency — a characteristic known as dispersion - delays measured on two or more frequency bands can be used to measure dispersion, and this measurement can then be used to estimate the delay at each frequency.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ The effects for any particular geographical area can be easily calculated by comparing the GPS-measured position to a known surveyed location.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ Some military and expensive survey-grade civilian receivers measure the different delays in the L1 and L2 frequencies to measure atmospheric dispersion, and apply a more precise correction.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

[58] .Some military and expensive survey-grade civilian receivers calculate atmospheric dispersion from the different delays in the L1 and L2 frequencies, and apply a more precise correction.^ Some military and expensive survey-grade civilian receivers measure the different delays in the L1 and L2 frequencies to measure atmospheric dispersion, and apply a more precise correction.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ Apply some corrections.
  • Global Positioning System 27 January 2010 23:56 UTC michna.com [Source type: FILTERED WITH BAYES]

^ Since the GPS receiver computes its approximate altitude, this error is relatively simple to correct, either by applying a function regression or correlating margin of atmospheric error to ambient pressure using a barometric altimeter.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

.This can be done in civilian receivers without decrypting the P(Y) signal carried on L2, by tracking the carrier wave instead of the modulated code.^ The L1 carrier is modulated by both the C/A and P codes, while the L2 carrier is only modulated by the P code.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ It allows a direct comparison of the L1 and L2 signals using the coded signal instead of the carrier wave.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ This can be done in civilian receivers without decrypting the P(Y) signal carried on L2, by tracking the carrier wave instead of the modulated code.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

.To facilitate this on lower cost receivers, a new civilian code signal on L2, called L2C, was added to the Block IIR-M satellites, which was first launched in 2005. It allows a direct comparison of the L1 and L2 signals using the coded signal instead of the carrier wave.^ This can be done in civilian receivers without decrypting the P(Y) signal carried on L2, by tracking the carrier wave instead of the modulated code.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ In 2005, the first modernized GPS satellite was launched and began transmitting a second civilian signal (L2C) for enhanced user performance.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ It allows a direct comparison of the L1 and L2 signals using the coded signal instead of the carrier wave.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

(see Atmospheric Effects in "Sources of Errors in GPS")
.The effects of the ionosphere generally change slowly, and can be averaged over time.^ Variation changes with location and (slowly) over time.
  • Micro Modular Technologies - GPS and Wireless Modules - Support 27 January 2010 23:56 UTC www.micro-modular.com [Source type: Reference]

^ The effects of the ionosphere generally change slowly, and can be averaged over time.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ This effect is called the "modifiable aerial unit problem" and, because changing the shape or size of the units on which data are mapped will change average values of the variables recorded, this can change the resulting correlations or statistical models generated from the data [ 18 ].
  • International Journal of Health Geographics | Full text | Development of a wearable global positioning system for place and health research 27 January 2010 23:56 UTC www.ij-healthgeographics.com [Source type: Academic]

.Those for any particular geographical area can be easily calculated by comparing the GPS-measured position to a known surveyed location.^ The effects for any particular geographical area can be easily calculated by comparing the GPS-measured position to a known surveyed location.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ Accurate measurement of the relative positions of two receivers tracking the same GPS signals.
  • Micro Modular Technologies - GPS and Wireless Modules - Support 27 January 2010 23:56 UTC www.micro-modular.com [Source type: Reference]

^ Contrast with 2D Operating Mode A measure indicating how closely the reported GPS position matches the true position.
  • Micro Modular Technologies - GPS and Wireless Modules - Support 27 January 2010 23:56 UTC www.micro-modular.com [Source type: Reference]

.This correction is also valid for other receivers in the same general location.^ This correction is also valid for other receivers in the same general location.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ A receiver set up at a known location for specifically collecting data to differentially correct rover files.
  • Micro Modular Technologies - GPS and Wireless Modules - Support 27 January 2010 23:56 UTC www.micro-modular.com [Source type: Reference]

^ Several systems send this information over radio or other links to allow L1-only receivers to make ionospheric corrections.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

.Several systems send this information over radio or other links to allow L1-only receivers to make ionospheric corrections.^ Several systems send this information over radio or other links to allow L1-only receivers to make ionospheric corrections.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ Not only does the Garmin Rino 520 HCx GPS make navigation easier than ever, it includes a GMRS radio to communicate with your group and Position Reporting feature which sends out your location.

^ Typically, commercial receivers use the single frequency L1 C/A code only.
  • Micro Modular Technologies - GPS and Wireless Modules - Support 27 January 2010 23:56 UTC www.micro-modular.com [Source type: Reference]

.The ionospheric data are transmitted via satellite in Satellite Based Augmentation Systems (SBAS) such as WAAS (available in North America and Hawaii), EGNOS (Europe and Asia) or MSAS (Japan), which transmits it on the GPS frequency using a special pseudo-random noise sequence (PRN), so only one receiver and antenna are required.^ L2 Frequency- One of the carrier frequencies transmitted by the GPS satellites.
  • Micro Modular Technologies - GPS and Wireless Modules - Support 27 January 2010 23:56 UTC www.micro-modular.com [Source type: Reference]

^ Garmin GPS 18x USB receiver for PC Antenna Only .
  • Garmin GPS Units: Portable handheld Car and Marine 13 January 2010 11:56 UTC www.thegpsstore.com [Source type: General]

^ The corrections are not as accurate as augmentation systems like WAAS or dual-frequency receivers.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

.Humidity also causes a variable delay, resulting in errors similar to ionospheric delay, but occurring in the troposphere.^ Humidity also causes a variable delay, resulting in errors similar to ionospheric delay, but occurring in the troposphere .
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ These traits make precise measurement and compensation of humidity errors more difficult than ionospheric effects.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ The sum of these atmospheric effects can result in errors of 30 to 60 m and vary depending on the angle of inclination of the satellites in view [ 41 ].
  • International Journal of Health Geographics | Full text | Development of a wearable global positioning system for place and health research 27 January 2010 23:56 UTC www.ij-healthgeographics.com [Source type: Academic]

.This effect both is more localized and changes more quickly than ionospheric effects, and is not frequency dependent.^ In both directions the change is dependent on a reference location.
  • International Journal of Health Geographics | Full text | Development of a wearable global positioning system for place and health research 27 January 2010 23:56 UTC www.ij-healthgeographics.com [Source type: Academic]

.These traits make precise measurement and compensation of humidity errors more difficult than ionospheric effects.^ These traits make precise measurement and compensation of humidity errors more difficult than ionospheric effects.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ These effects also reduce the more precise P(Y) code's accuracy.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ There is some evidence that different makes and models of various GPS units are slightly more accurate than others.
  • A Practical Guide to GPS -UTM 13 January 2010 11:56 UTC www.dbartlett.com [Source type: FILTERED WITH BAYES]

[citation needed]
.Changes in receiver altitude also change the amount of delay, due to the signal passing through less of the atmosphere at higher elevations.^ Changes in receiver altitude also change the amount of delay, due to the signal passing through less of the atmosphere at higher elevations.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ Differential-enabled GPS receivers can receive the broadcast DGPS signals from the ground stations and make correction calculations, improving accuracy of position to within 3 m or less.
  • International Journal of Health Geographics | Full text | Development of a wearable global positioning system for place and health research 27 January 2010 23:56 UTC www.ij-healthgeographics.com [Source type: Academic]

^ Pseudorange differs from the actual range by the amount that the satellite and receiver clocks are offset, by propagation delays, and other errors including those introduced by selective availability.
  • Micro Modular Technologies - GPS and Wireless Modules - Support 27 January 2010 23:56 UTC www.micro-modular.com [Source type: Reference]

.Since the GPS receiver computes its approximate altitude, this error is relatively simple to correct, either by applying a function regression or correlating margin of atmospheric error to ambient pressure using a barometric altimeter.^ Correcting a GPS receiver's clock .
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ Since the GPS receiver computes its approximate altitude, this error is relatively simple to correct, either by applying a function regression or correlating margin of atmospheric error to ambient pressure using a barometric altimeter.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ Artillery projectiles with embedded GPS receivers able to withstand accelerations of 12,000 G have been developed for use in 155 mm howitzers .
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

[citation needed]

Multipath effects

.GPS signals can also be affected by multipath issues, where the radio signals reflect off surrounding terrain; buildings, canyon walls, hard ground, etc.^ The GPS unit does not send out radio signals, it only receives them.
  • A Practical Guide to GPS -UTM 13 January 2010 11:56 UTC www.dbartlett.com [Source type: FILTERED WITH BAYES]

^ Uplink- A transmission path by which radio or other signals are sent from the ground to an aircraft or a communications satellite.
  • Micro Modular Technologies - GPS and Wireless Modules - Support 27 January 2010 23:56 UTC www.micro-modular.com [Source type: Reference]

^ Pseudo-lite- A ground-based transmitter transmits a signal like that of an actual GPS satellite which can be used for ranging.
  • Micro Modular Technologies - GPS and Wireless Modules - Support 27 January 2010 23:56 UTC www.micro-modular.com [Source type: Reference]

.These delayed signals can cause inaccuracy.^ These delayed signals can cause inaccuracy.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ Short delay reflections are harder to filter out because they interfere with the true signal, causing effects almost indistinguishable from routine fluctuations in atmospheric delay.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

A variety of techniques, most notably narrow correlator spacing, have been developed to mitigate multipath errors. .For long delay multipath, the receiver itself can recognize the wayward signal and discard it.^ For long delay multipath, the receiver itself can recognize the wayward signal and discard it.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ Changes in receiver altitude also change the amount of delay, due to the signal passing through less of the atmosphere at higher elevations.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ To address shorter delay multipath from the signal reflecting off the ground, specialized antennas (e.g.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

.To address shorter delay multipath from the signal reflecting off the ground, specialized antennas (e.g., a choke ring antenna) may be used to reduce the signal power as received by the antenna.^ To address shorter delay multipath from the signal reflecting off the ground, specialized antennas (e.g.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ GPS signals can also be affected by multipath issues, where the radio signals reflect off surrounding terrain; buildings, canyon walls, hard ground, etc.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ Doppler Aiding- A signal processing strategy that uses a measured doppler shift to help the receiver smoothly track the GPS signal.
  • Micro Modular Technologies - GPS and Wireless Modules - Support 27 January 2010 23:56 UTC www.micro-modular.com [Source type: Reference]

.Short delay reflections are harder to filter out because they interfere with the true signal, causing effects almost indistinguishable from routine fluctuations in atmospheric delay.^ Short delay reflections are harder to filter out because they interfere with the true signal, causing effects almost indistinguishable from routine fluctuations in atmospheric delay.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ These delayed signals can cause inaccuracy.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ Basic and simple to use Rating:3 out of 5 stars This case is easy to use but may be a little short for the 4″ wide GPS systems as they stick out a bit.
  • Garmin 3.5Inch Carrying Case | Ultra Gps 16 January 2010 16:26 UTC ultra-gps.com [Source type: FILTERED WITH BAYES]

.Multipath effects are much less severe in moving vehicles.^ Multipath effects are much less severe in moving vehicles.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

.When the GPS antenna is moving, the false solutions using reflected signals quickly fail to converge and only the direct signals result in stable solutions.^ The GPS will only give direction when it (and you) are moving.
  • A Practical Guide to GPS -UTM 13 January 2010 11:56 UTC www.dbartlett.com [Source type: FILTERED WITH BAYES]

^ P-Code- The precise code of the GPS signal typically used only by the U.S. military.
  • Micro Modular Technologies - GPS and Wireless Modules - Support 27 January 2010 23:56 UTC www.micro-modular.com [Source type: Reference]

^ When the GPS antenna is moving, the false solutions using reflected signals quickly fail to converge and only the direct signals result in stable solutions.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

Ephemeris and clock errors

.While the ephemeris data is transmitted every 30 seconds, the information itself may be up to two hours old.^ The data may be used for several hours and is normally refreshed every two hours.
  • Micro Modular Technologies - GPS and Wireless Modules - Support 27 January 2010 23:56 UTC www.micro-modular.com [Source type: Reference]

^ While the ephemeris data is transmitted every 30 seconds, the information itself may be up to two hours old.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ There can be a delay of up to 30 seconds before the first estimate of position because of the need to read the epheremis data before computing the intersections of sphere surfaces.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

.If a fast time to first fix (TTFF) is needed, it is possible to upload a valid ephemeris to a receiver, and in addition to setting the time, a position fix can be obtained in under ten seconds.^ Time To First Fix (TTFF) - The time it takes a GPS receiver to report a valid fix from startup.
  • Micro Modular Technologies - GPS and Wireless Modules - Support 27 January 2010 23:56 UTC www.micro-modular.com [Source type: Reference]

^ If a fast Time To First Fix (TTFF) is needed, it is possible to upload a valid ephemeris to a receiver, and in addition to setting the time, a position fix can be obtained in under ten seconds.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ The time it takes a GPS receiver to report a valid fix from startup.
  • Micro Modular Technologies - GPS and Wireless Modules - Support 27 January 2010 23:56 UTC www.micro-modular.com [Source type: Reference]

.It is feasible to put such ephemeris data on the web so it can be loaded into mobile GPS devices.^ It is feasible to put such ephemeris data on the web so it can be loaded into mobile GPS devices.See also Assisted GPS .
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ GPS receivers come in a variety of formats, from devices integrated into cars, phones, and watches, to dedicated devices such as those shown here from manufacturers Trimble , Garmin and Leica (left to right).
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ The two-way transfer of GPS information with another device, such as a nav plotter, autopilot, or another GPS unit.
  • Micro Modular Technologies - GPS and Wireless Modules - Support 27 January 2010 23:56 UTC www.micro-modular.com [Source type: Reference]

[59] .See also Assisted GPS.^ It is feasible to put such ephemeris data on the web so it can be loaded into mobile GPS devices.See also Assisted GPS .
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

.The satellite's atomic clocks experience noise and clock drift errors.^ The satellite's atomic clocks experience noise and clock drift errors.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ Satellite clock errors .
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ Because of the very large value of the speed of light , c , the estimated distances from the GPS receiver to the satellites, the pseudoranges, are very sensitive to errors in the GPS receiver clock.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

.The navigation message contains corrections for these errors and estimates of the accuracy of the atomic clock.^ Where DGPS radio stations broadcasting the corrections to be applied because of SA are locally available, and these corrections are fed to the GPS unit, accuracy is much improved, perhaps giving an error of 20 metres instead of closer to 100.
  • A Practical Guide to GPS -UTM 13 January 2010 11:56 UTC www.dbartlett.com [Source type: FILTERED WITH BAYES]

^ The average of all logged coordinates was compared with the known geodetic point to obtain an estimate of the accuracy of each instrument and to evaluate the total mean error from all four instruments.
  • International Journal of Health Geographics | Full text | Development of a wearable global positioning system for place and health research 27 January 2010 23:56 UTC www.ij-healthgeographics.com [Source type: Academic]

^ A base station calculates the error for each satellite, improving the accuracy of GPS positions collected at unknown locations by a roving GPS receiver through differential correction.
  • Micro Modular Technologies - GPS and Wireless Modules - Support 27 January 2010 23:56 UTC www.micro-modular.com [Source type: Reference]

.However, they are based on observations and may not indicate the clock's current state.^ However, they are based on observations and may not indicate the clock's current state.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ Another useful form of these equations is in terms of the pseudoranges , which are simply the ranges approximated based on GPS receiver clock's indicated (i.e.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ However, this may be misleading since they are actually deterministic sequences.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

.These problems tend to be very small, but may add up to a few meters (tens of feet) of inaccuracy.^ These problems tend to be very small, but may add up to a few meters (10s of feet) of inaccuracy.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ When I am travelling in the bush, my GPS is at the back of my head, securely closed up in a very small belted pack, in a platic bag and turned on to record track.
  • A Practical Guide to GPS -UTM 13 January 2010 11:56 UTC www.dbartlett.com [Source type: FILTERED WITH BAYES]

[60]
.For very precise positioning (e.g., in geodesy), these effects can be eliminated by differential GPS: the simultaneous use of two or more receivers at several survey points.^ These effects also reduce the more precise P(Y) code's accuracy.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ Artillery projectiles with embedded GPS receivers able to withstand accelerations of 12,000 G have been developed for use in 155 mm howitzers .
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ Two GPS developers received the National Academy of Engineering Charles Stark Draper Prize for 2003: .
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

.In the 1990s when receivers were quite expensive, some methods of quasi-differential GPS were developed, using only one receiver but reoccupation of measuring points.^ Also it has been claimed that this method is the "typical" method used by GPS receivers.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ Artillery projectiles with embedded GPS receivers able to withstand accelerations of 12,000 G have been developed for use in 155 mm howitzers .
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ Two GPS developers received the National Academy of Engineering Charles Stark Draper Prize for 2003: .
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

At the TU Vienna the method was named qGPS and adequate software of post processing was developed.

Geometric dilution of precision computation (GDOP)

.The concept of geometric dilution of precision was introduced in the section, error sources and analysis.^ Geometric dilution of precision computation (DOP) .
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ Error sources and analysis .
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ The standard deviation of the error in receiver position, , is computed by multiplying PDOP (Position Dilution Of Precision) by , the standard deviation of the user equivalent range errors.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

.Computations were provided to show how PDOP was used and how it affected the receiver position error standard deviation.^ The standard deviation of the error in receiver position, , is computed by multiplying PDOP (Position Dilution Of Precision) by , the standard deviation of the user equivalent range errors.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ PDOP is computed as a function of receiver and satellite positions.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ The standard deviation of the error in estimated receiver position, , is given by for the C/A code.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

.When visible GPS satellites are close together in the sky (i.e., small angular separation), the DOP values are high; when far apart, the DOP values are low.^ The antenna has a 2 m cable and can be positioned appropriately to maximize visibility of the sky and satellite signal reception.
  • International Journal of Health Geographics | Full text | Development of a wearable global positioning system for place and health research 27 January 2010 23:56 UTC www.ij-healthgeographics.com [Source type: Academic]

^ When you turn on your GPS and point the antenna to the sky, it starts picking up signals from the satellites, starting with the strongest signal.
  • A Practical Guide to GPS -UTM 13 January 2010 11:56 UTC www.dbartlett.com [Source type: FILTERED WITH BAYES]

^ Because of the very large value of the speed of light , c , the estimated distances from the GPS receiver to the satellites, the pseudoranges, are very sensitive to errors in the GPS receiver clock.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

.Conceptually, satellites that are close together cannot provide as much information as satellites that are widely separated.^ Wide Area Augmentation System (WAAS) - A system of satellites and ground stations that provide GPS signal corrections for better position accuracy.
  • Micro Modular Technologies - GPS and Wireless Modules - Support 27 January 2010 23:56 UTC www.micro-modular.com [Source type: Reference]

.Low DOP values represent a better GPS positional accuracy due to the wider angular separation between the satellites used to calculate GPS receiver position.^ Using messages received from four satellites, the GPS receiver is able to determine the satellite positions and time sent.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ The GPS receiver's reported position coordinates.
  • Micro Modular Technologies - GPS and Wireless Modules - Support 27 January 2010 23:56 UTC www.micro-modular.com [Source type: Reference]

^ The difference between the clock time maintained in the GPS receiver and GPS satellite time.
  • Micro Modular Technologies - GPS and Wireless Modules - Support 27 January 2010 23:56 UTC www.micro-modular.com [Source type: Reference]

.HDOP, VDOP, PDOP and TDOP are respectively Horizontal, Vertical, Position (3-D) and Time Dilution of Precision.^ Position Dilution of Precision (PDOP) - See Dilution of Precision DOP .
  • Micro Modular Technologies - GPS and Wireless Modules - Support 27 January 2010 23:56 UTC www.micro-modular.com [Source type: Reference]

^ Contrast with Quadrifilar Helix Antenna Abbreviation for Position Dilution of Precision See Dilution of Precision DOP .
  • Micro Modular Technologies - GPS and Wireless Modules - Support 27 January 2010 23:56 UTC www.micro-modular.com [Source type: Reference]

^ The standard deviation of the error in receiver position, , is computed by multiplying PDOP (Position Dilution Of Precision) by , the standard deviation of the user equivalent range errors.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

.Figure 3.1 Dilution of Precision of [22] provide a graphical indication of how geometry affect accuracy.^ A lower DOP value indicates better geometry and correspondingly higher accuracy.
  • Micro Modular Technologies - GPS and Wireless Modules - Support 27 January 2010 23:56 UTC www.micro-modular.com [Source type: Reference]

^ Also a more detailed description of how to calculate PDOP is given in the section, Geometric dilution of precision computation (DOP) .
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ Accuracy- A measure indicating how closely the reported GPS position matches the true position.
  • Micro Modular Technologies - GPS and Wireless Modules - Support 27 January 2010 23:56 UTC www.micro-modular.com [Source type: Reference]

.We now take on the task of how to compute the dilution of precision terms.^ Geometric dilution of precision computation (DOP) .
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ The standard deviation of the error in receiver position, , is computed by multiplying PDOP (Position Dilution Of Precision) by , the standard deviation of the user equivalent range errors.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ The equations for computing the geometric dilution of precision terms have been described in the previous section.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

As a first step in computing DOP, consider the unit vector from the receiver to satellite i with components \frac{(x_i- x)}{R_i}, \frac {(y_i-y)}{R_i}, and \frac {(z_i-z)}{R_i} where the distance from receiver to the satellite, \ R_i , is given by:
R_i\,=\,\sqrt{(x_i- x)^2 + (y_i-y)^2 + (z_i-z)^2}
where .\ x, y, and\ z denote the position of the receiver and \ x_i, y_i, and\ z_i denote the position of satellite i.^ Acquisition Time- Period required by a GPS receiver to determine initial position based on acquisition of satellite signals.
  • Micro Modular Technologies - GPS and Wireless Modules - Support 27 January 2010 23:56 UTC www.micro-modular.com [Source type: Reference]

^ See Navigation Sensitivity and Tracking Sensitivity Period required by a GPS receiver to determine initial position based on acquisition of satellite signals.
  • Micro Modular Technologies - GPS and Wireless Modules - Support 27 January 2010 23:56 UTC www.micro-modular.com [Source type: Reference]

^ It may involve acquiring satellite signals, receiving almanac and ephemeris, calculating pseudoranges, and developing a position estimate.
  • Micro Modular Technologies - GPS and Wireless Modules - Support 27 January 2010 23:56 UTC www.micro-modular.com [Source type: Reference]

.These x, y, and z components may be components in a North, East, Down coordinate system a South, East, Up coordinate system or other convenient system.^ In using UTM grid coordinates, the "easting" from the zone meridian is always given first, and then the "northing".
  • A Practical Guide to GPS -UTM 13 January 2010 11:56 UTC www.dbartlett.com [Source type: FILTERED WITH BAYES]

^ In other words, the easting is always given before the northing.
  • A Practical Guide to GPS -UTM 13 January 2010 11:56 UTC www.dbartlett.com [Source type: FILTERED WITH BAYES]

^ The other 14 digit number must be broken up: 0439535 is the EASTING from the zone 18 meridian, down to the closest metre.
  • A Practical Guide to GPS -UTM 13 January 2010 11:56 UTC www.dbartlett.com [Source type: FILTERED WITH BAYES]

Formulate the matrix A as:
A = \begin{bmatrix} \frac {(x_1- x)} {R_1} & \frac {(y_1-y)} {R_1} & \frac {(z_1-z)} {R_1} & c \ \frac {(x_2- x)} {R_2} & \frac {(y_2-y)} {R_2} & \frac {(z_2-z)} {R_2} & c \ \frac {(x_3- x)} {R_3} & \frac {(y_3-y)} {R_3} & \frac {(z_3-z)} {R_3} & c \ \frac {(x_4- x)} {R_4} & \frac {(y_4-y)} {R_4} & \frac {(z_4-z)} {R_4} & c \end{bmatrix}
.The first three elements of each row of A are the components of a unit vector from the receiver to the indicated satellite.^ As a first step in computing DOP, consider the unit vector from the receiver to satellite i with components, .
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ Consider the unit vectors pointing from the receiver to the satellites.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ Formulate the matrix A as The first three elements of each row of A are the components of a unit vector from the receiver to the indicated satellite.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

.The elements in the fourth column are c where c denotes the speed of light.^ The elements in the fourth column are c where c denotes the speed of light .
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

Formulate the matrix, Q, as
 Q = \left (A^T A \right )^{-1}
.This computation is in accordance with Chapter 11 of The global positioning system by Parkinson and Spilker where the weighting matrix, P, has been set to the identity matrix.^ This computation is in accordance with "Section 1.4.2 of PRINCIPLES OF SATELLITE POSITIONING" where the weighting matrix, P, has been set to the identity matrix.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ Submissions for the collection: Global Positioning System .
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ GPS (Global Positioning System) is one of the technical marvels of our time.
  • Global Positioning System 27 January 2010 23:56 UTC michna.com [Source type: FILTERED WITH BAYES]

The elements of the Q matrix are designated as:
Q = \begin{bmatrix} d_x^2 & d_{xy}^2 & d_{xz}^2 & d_{xt}^2 \ d_{xy}^2 & d_{y}^2 & d_{yz}^2 & d_{yt}^2 \ d_{xz}^2 & d_{yz}^2 & d_{z}^2 & d_{zt}^2 \ d_{xt}^2 & d_{yt}^2 & d_{zt}^2 & d_{t}^2 \end{bmatrix}
.The Greek letter \ \sigma is used quite often where we have used d.^ The Greek letter is used quite often where we have used d.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

.However the elements of the Q matrix do not represent variances and covariances as they are defined in probability and statistics.^ However the elements of the Q matrix do not represent variances and covariances as they are defined in probability and statistics.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ Assuming the pseudorange errors are uncorrelated and have the same variance, the covariance matrix on the right side can be expressed as a scalar times the identity matrix.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

.Instead they are strictly geometric terms.^ Instead they are strictly geometric terms.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

.Therefore d as in dilution of precision is used.^ Therefore d as in dilution of precision is used.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ The horizontal dilution of precision, , and the vertical dilution of precision, , are both dependent on the coordinate system used.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

PDOP, TDOP and GDOP are given by
PDOP = \sqrt{d_x^2 + d_y^2 + d_z^2},
\ TDOP = \sqrt{d_{t}^2} = |d_{t}|\ , and
 GDOP = \sqrt{PDOP^2 + TDOP^2}
.The horizontal dilution of precision,  HDOP = \sqrt{d_x^2 + d_y^2}, and the vertical dilution of precision, \ VDOP = \sqrt{d_{z}^2}, are both dependent on the coordinate system used.^ Grid- A pattern of regularly spaced horizontal and vertical lines forming square zones on a map used as a reference for establishing points.
  • Micro Modular Technologies - GPS and Wireless Modules - Support 27 January 2010 23:56 UTC www.micro-modular.com [Source type: Reference]

^ UTM is the primary coordinate system used on U.S. Geological Survey topographic maps.
  • Micro Modular Technologies - GPS and Wireless Modules - Support 27 January 2010 23:56 UTC www.micro-modular.com [Source type: Reference]

^ A pattern of regularly spaced horizontal and vertical lines forming square zones on a map used as a reference for establishing points.
  • Micro Modular Technologies - GPS and Wireless Modules - Support 27 January 2010 23:56 UTC www.micro-modular.com [Source type: Reference]

.To correspond to the local horizon plane and the local vertical, x, y, and z should denote positions in either a North, East, Down coordinate system or a South, East, Up coordinate system.^ Latitude- The angular distance north or south from the equator of a position.
  • Micro Modular Technologies - GPS and Wireless Modules - Support 27 January 2010 23:56 UTC www.micro-modular.com [Source type: Reference]

^ See Local Area Augmentation System The angular distance north or south from the equator of a position.
  • Micro Modular Technologies - GPS and Wireless Modules - Support 27 January 2010 23:56 UTC www.micro-modular.com [Source type: Reference]

^ A system of plane coordinates based upon 60 north-south trending zones, each 6 degrees of longitude wide, that circle the globe.
  • Micro Modular Technologies - GPS and Wireless Modules - Support 27 January 2010 23:56 UTC www.micro-modular.com [Source type: Reference]

Derivation of DOP equations

.The equations for computing the geometric dilution of precision terms have been described in the previous section.^ Geometric Dilution of Precision (GDOP) - See Dilution of Precision DOP .
  • Micro Modular Technologies - GPS and Wireless Modules - Support 27 January 2010 23:56 UTC www.micro-modular.com [Source type: Reference]

^ GDOP- Abbreviation for Geometric Dilution of Precision See Dilution of Precision DOP .
  • Micro Modular Technologies - GPS and Wireless Modules - Support 27 January 2010 23:56 UTC www.micro-modular.com [Source type: Reference]

^ See Federal Radionavigation Plan The proposed European counterpart to GPS Abbreviation for Geometric Dilution of Precision See Dilution of Precision DOP .
  • Micro Modular Technologies - GPS and Wireless Modules - Support 27 January 2010 23:56 UTC www.micro-modular.com [Source type: Reference]

This section describes the derivation of these equations. The method used here is similar to that used in "Global Positioning System (preview) by Parkinson and Spiker"
.Consider the position error vector, \mathbf{e}, defined as the vector from the intersection of the four sphere surfaces corresponding to the pseudoranges to the true position of the receiver.^ CEP is defined as the radius of a circle (centered on the true position) that contains 50% of the reported positions.
  • Micro Modular Technologies - GPS and Wireless Modules - Support 27 January 2010 23:56 UTC www.micro-modular.com [Source type: Reference]

^ See Differential GPS A technique to improve position accuracy by supplying pseudorange corrections transmitted by a Beacon close to the GPS receiver.
  • Micro Modular Technologies - GPS and Wireless Modules - Support 27 January 2010 23:56 UTC www.micro-modular.com [Source type: Reference]

^ Contrast with 3D Operating Mode The mode of operation in which a GPS receiver computes a position using at least four Pseudorange measurements.
  • Micro Modular Technologies - GPS and Wireless Modules - Support 27 January 2010 23:56 UTC www.micro-modular.com [Source type: Reference]

\mathbf{e} = e_x\hat{x} + e_y\hat{y} + e_z\hat{z} where bold denotes a vector and \hat{x}, \hat{y}, and \hat{z} denote unit vectors along the x, y, and z axes respectively. Let \ e_t denote the time error, the true time minus the receiver indicated time. Assume that the mean value of the three components of \mathbf {e} and \ e_t are zero.
A\ \begin{bmatrix} e_x \\ e_y \\ e_z \\ e_t \end{bmatrix} = \begin{bmatrix} \frac {(x_1- x)} {R_1} & \frac {(y_1-y)} {R_1} & \frac {(z_1-z)} {R_1} & c \ \frac {(x_2- x)} {R_2} & \frac {(y_2-y)} {R_2} & \frac {(z_2-z)} {R_2} & c \ \frac {(x_3- x)} {R_3} & \frac {(y_3-y)} {R_3} & \frac {(z_3-z)} {R_3} & c \ \frac {(x_4- x)} {R_4} & \frac {(y_4-y)} {R_4} & \frac {(z_4-z)} {R_4} & c \end{bmatrix}\ \begin{bmatrix} e_x \\ e_y \\ e_z \\ e_t \end{bmatrix} = \begin{bmatrix} e_1 \\ e_2 \\ e_3 \\ e_4 \end{bmatrix} \ (1)
where \ e_1,\ e_2,\ e_3,\ and\ e_4 are the errors in pseudoranges 1 through 4 respectively. .This equation comes from linearizing the equation relating pseudoranges to receiver position, satellite positions, and receiver clock errors as shown in.^ This equation comes from linearizing the equation relating pseudoranges to receiver position, satellite positions, and receiver clock errors as shown in .
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ The satellite clock errors will be approximately eliminated by this between receiver differencing.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ Satellite clock errors .
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

[61] Multiplying both sides by \ A^{-1}\ there results
\ \begin{bmatrix} e_x \\ e_y \\ e_z \\ e_t \end{bmatrix} = A^{-1} \begin{bmatrix} e_1 \\ e_2 \\ e_3 \\ e_4 \end{bmatrix} \ (2) .
Transposing both sides:
\ \begin{bmatrix} e_x & e_y & e_z & e_t \end{bmatrix} = \begin{bmatrix} e_1 & e_2 & e_3 & e_4 \end{bmatrix}\left (A^{-1} \right )^T \ (3) .
Post multiplying the matrices on both sides of equation (2) by the corresponding matrices in equation (3), there results
\ \begin{bmatrix} e_x \\ e_y \\ e_z \\ e_t \end{bmatrix} \begin{bmatrix} e_x & e_y & e_z & e_t \end{bmatrix} = A^{-1} \begin{bmatrix} e_1 \\ e_2 \\ e_3 \\ e_4 \end{bmatrix} \begin{bmatrix} e_1 & e_2 & e_3 & e_4 \end{bmatrix}\left (A^{-1} \right )^T \ (4) .
Taking the expected value of both sides and taking the non-random matrices outside the expectation operator, E, there results:
\ E \left (\begin{bmatrix} e_x \\ e_y \\ e_z \\ e_t \end{bmatrix} \begin{bmatrix} e_x & e_y & e_z & e_t \end{bmatrix} \right ) = A^{-1} \ E \left (\begin{bmatrix} e_1 \\ e_2 \\ e_3 \\ e_4 \end{bmatrix} \begin{bmatrix} e_1 & e_2 & e_3 & e_4 \end{bmatrix} \right ) \left (A^{-1} \right )^T \ (5)
.Assuming the pseudorange errors are uncorrelated and have the same variance, the covariance matrix on the right side can be expressed as a scalar times the identity matrix.^ Assuming the pseudorange errors are uncorrelated and have the same variance, the covariance matrix on the right side can be expressed as a scalar times the identity matrix.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ Pseudorange- A measure of the apparent propagation time from the satellite to the receiver antenna, expressed as a distance.
  • Micro Modular Technologies - GPS and Wireless Modules - Support 27 January 2010 23:56 UTC www.micro-modular.com [Source type: Reference]

^ The remaining position and time error variance terms follow in a straightforward manner.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

Thus
 \begin{bmatrix} \sigma_x^2 & \sigma_{xy}^2 & \sigma_{xz}^2 & \sigma_{xt}^2 \ \sigma_{xy}^2 & \sigma_{y}^2 & \sigma_{yz}^2 & \sigma_{yt}^2 \ \sigma_{xz}^2 & \sigma_{yz}^2 & \sigma_{z}^2 & \sigma_{zt}^2 \ \sigma_{xt}^2 & \sigma_{yt}^2 & \sigma_{zt}^2 & \sigma_{t}^2 \end{bmatrix} = \sigma_R^2 \ A^{-1} \left (A^{-1} \right )^T = \sigma_R^2 \ \left (A^T A \right )^{-1} \ (6)
since \ A^{-1} \left (A^{-1} \right )^T \left (A^T A \right ) = I
Note: \left (A^{-1} \right )^T = \left (A^{T} \right )^{-1},\ since \ I = \left(A A^{-1}\right)^T = \left(A^{-1}\right)^T A^T
Substituting for \left (A^T A \right )^{-1} = Q there follows
 \begin{bmatrix} \sigma_x^2 & \sigma_{xy}^2 & \sigma_{xz}^2 & \sigma_{xt}^2 \ \sigma_{xy}^2 & \sigma_{y}^2 & \sigma_{yz}^2 & \sigma_{yt}^2 \ \sigma_{xz}^2 & \sigma_{yz}^2 & \sigma_{z}^2 & \sigma_{zt}^2 \ \sigma_{xt}^2 & \sigma_{yt}^2 & \sigma_{zt}^2 & \sigma_{t}^2 \end{bmatrix} = \sigma_R^2 \ \begin{bmatrix} d_x^2 & d_{xy}^2 & d_{xz}^2 & d_{xt}^2 \ d_{xy}^2 & d_{y}^2 & d_{yz}^2 & d_{yt}^2 \ d_{xz}^2 & d_{yz}^2 & d_{z}^2 & d_{zt}^2 \ d_{xt}^2 & d_{yt}^2 & d_{zt}^2 & d_{t}^2 \end{bmatrix} \ (7)
From equation (7), it follows that the variances of indicated receiver position and time are
\sigma_{rc}^2 = \sigma_x^2 + \sigma_y^2 + \sigma_z^2 = \sigma_R^2\left(d_x^2 + d_y^2 + d_z^2\right) = PDOP^2 \sigma_R^2 and
\sigma_t^2 = \sigma_R^2 d_t^2 = TDOP^2 \sigma_R^2
.The remaining position and time error variance terms follow in a straightforward manner.^ The remaining position and time error variance terms follow in a straightforward manner.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ From equation (7), it follows that the variances of indicated receiver position and time are .
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ Assuming the pseudorange errors are uncorrelated and have the same variance, the covariance matrix on the right side can be expressed as a scalar times the identity matrix.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

Selective availability

.GPS includes a (currently disabled) feature called Selective Availability (SA) that adds intentional, time varying errors of up to 100 meters (328 ft) to the publicly available navigation signals.^ GPS includes a (currently disabled) feature called Selective Availability ( SA ) that can introduce intentional, slowly changing random errors of up to a hundred meters (328 ft) into the publicly available navigation signals to confound, for example, the guidance of long range missiles to precise targets.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ Assuming the pseudorange errors are uncorrelated and have the same variance, the covariance matrix on the right side can be expressed as a scalar times the identity matrix.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ The format includes definitions for three fundamental GPS observables: time, phase, and range.
  • Micro Modular Technologies - GPS and Wireless Modules - Support 27 January 2010 23:56 UTC www.micro-modular.com [Source type: Reference]

.This was intended to deny an enemy the use of civilian GPS receivers for precision weapon guidance.^ GPS tours are also an example of civilian use.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ Artillery projectiles with embedded GPS receivers able to withstand accelerations of 12,000 G have been developed for use in 155 mm howitzers .
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ GPS is often used by civilians as a navigation system.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

.SA errors are actually pseudorandom, generated by a cryptographic algorithm from a classified seed key available only to authorized users (the U.S. military, its allies and a few other users, mostly government) with a special military GPS receiver.^ When enabled, the accuracy is still available in the signal, but in an encrypted form that is only available to the United States military, its allies and a few others, mostly government users.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ Precise Positioning Service (PPS) - The GPS positioning service available only to authorized users with a key to decrypt the P(Y) code.
  • Micro Modular Technologies - GPS and Wireless Modules - Support 27 January 2010 23:56 UTC www.micro-modular.com [Source type: Reference]

^ See Precise Positioning Service The GPS positioning service available only to authorized users with a key to decrypt the P(Y) code.
  • Micro Modular Technologies - GPS and Wireless Modules - Support 27 January 2010 23:56 UTC www.micro-modular.com [Source type: Reference]

.Mere possession of the receiver is insufficient; it still needs the tightly controlled daily key.^ Even those who have managed to acquire military GPS receivers would still need to obtain the daily key , whose dissemination is tightly controlled.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

.Before it was turned off on May 1, 2000, typical SA errors were about 50 m (164 ft) horizontally and about 100 m (328 ft) vertically.^ SA has been turned off since 2000 by presidential order.
  • Micro Modular Technologies - GPS and Wireless Modules - Support 27 January 2010 23:56 UTC www.micro-modular.com [Source type: Reference]

^ It knows turn-off lanes and directs you into them before actually reaching the turn-off itself.
  • Global Positioning System 27 January 2010 23:56 UTC michna.com [Source type: FILTERED WITH BAYES]

^ When you have only 1,600 ft altitude above ground left, then you have to turn towards the airfield, otherwise you may not make it.
  • Global Positioning System 27 January 2010 23:56 UTC michna.com [Source type: FILTERED WITH BAYES]

[62] .Because SA affects every GPS receiver in a given area almost equally, a fixed station with an accurately known position can measure the SA error values and transmit them to the local GPS receivers so they may correct their position fixes.^ Accurate measurement of the relative positions of two receivers tracking the same GPS signals.
  • Micro Modular Technologies - GPS and Wireless Modules - Support 27 January 2010 23:56 UTC www.micro-modular.com [Source type: Reference]

^ The GPS receiver's reported position coordinates.
  • Micro Modular Technologies - GPS and Wireless Modules - Support 27 January 2010 23:56 UTC www.micro-modular.com [Source type: Reference]

^ Position Fix- The GPS receiver's reported position coordinates.
  • Micro Modular Technologies - GPS and Wireless Modules - Support 27 January 2010 23:56 UTC www.micro-modular.com [Source type: Reference]

.This is called Differential GPS or DGPS.^ DGPS- See Differential GPS .
  • Micro Modular Technologies - GPS and Wireless Modules - Support 27 January 2010 23:56 UTC www.micro-modular.com [Source type: Reference]

^ Differential GPS (DGPS) - A technique to improve position accuracy by supplying pseudorange corrections transmitted by a Beacon close to the GPS receiver.
  • Micro Modular Technologies - GPS and Wireless Modules - Support 27 January 2010 23:56 UTC www.micro-modular.com [Source type: Reference]

.DGPS also corrects for several other important sources of GPS errors, particularly ionospheric delay, so it continues to be widely used even though SA has been turned off.^ After SA, which has been turned off, the largest error in GPS is usually the unpredictable delay through the ionosphere.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ Since the GPS receiver computes its approximate altitude, this error is relatively simple to correct, either by applying a function regression or correlating margin of atmospheric error to ambient pressure using a barometric altimeter.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ Basic and simple to use Rating:3 out of 5 stars This case is easy to use but may be a little short for the 4″ wide GPS systems as they stick out a bit.
  • Garmin 3.5Inch Carrying Case | Ultra Gps 16 January 2010 16:26 UTC ultra-gps.com [Source type: FILTERED WITH BAYES]

The ineffectiveness of SA in the face of widely available DGPS was a common argument for turning off SA, and this was finally done by order of President Clinton in 2000.
Another restriction on GPS, antispoofing, remains on. .This encrypts the P-code so that it cannot be mimicked by an enemy transmitter sending false information.^ Anti-Spoofing- The process of encrypting P-Code information so that it cannot be replicated by an adversary.
  • Micro Modular Technologies - GPS and Wireless Modules - Support 27 January 2010 23:56 UTC www.micro-modular.com [Source type: Reference]

^ Contrast with Digital Signal The process of encrypting P-Code information so that it cannot be replicated by an adversary.
  • Micro Modular Technologies - GPS and Wireless Modules - Support 27 January 2010 23:56 UTC www.micro-modular.com [Source type: Reference]

.Few civilian receivers have ever used the P-code, and the accuracy attainable with the public C/A code is so much better than originally expected (especially with DGPS) that the antispoof policy has relatively little effect on most civilian users.^ Typically, commercial receivers use the single frequency L1 C/A code only.
  • Micro Modular Technologies - GPS and Wireless Modules - Support 27 January 2010 23:56 UTC www.micro-modular.com [Source type: Reference]

^ Because of this, carrier frequency tracking along with PRN code tracking are used to determine when the received satellite's PRN code begins (see "How a GPS Receiver Gets a Lock" ).
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ However, it is often better than no correction, since ionospheric error is the largest error source for a single-frequency GPS receiver.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

.Turning off antispoof would primarily benefit surveyors and some scientists who need extremely precise positions for experiments such as tracking the motion of a tectonic plate.^ Ground Track- The plot of positions reported over time by a navigation device such as a GPS receiver.
  • Micro Modular Technologies - GPS and Wireless Modules - Support 27 January 2010 23:56 UTC www.micro-modular.com [Source type: Reference]

^ Even those who have managed to acquire military GPS receivers would still need to obtain the daily key , whose dissemination is tightly controlled.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

DGPS services are widely available from both commercial and government sources. .The latter include WAAS and the U.S. Coast Guard's network of LF marine navigation beacons.^ Beacon- A radio station (Operated by the Coast Guard in the US) that broadcasts Differential Corrections for GPS receivers to improve accuracy.
  • Micro Modular Technologies - GPS and Wireless Modules - Support 27 January 2010 23:56 UTC www.micro-modular.com [Source type: Reference]

^ In the US, DGPS beacons are operated by the Coast Guard.
  • Micro Modular Technologies - GPS and Wireless Modules - Support 27 January 2010 23:56 UTC www.micro-modular.com [Source type: Reference]

.The accuracy of the corrections depends on the distance between the user and the DGPS receiver.^ Satellite Based Augmentation System (SBAS) - A system designed to improve the accuracy of GPS using ground stations to monitor the GPS signals, calculate corrections, and then transmit them from satellites to the GPS receiver.
  • Micro Modular Technologies - GPS and Wireless Modules - Support 27 January 2010 23:56 UTC www.micro-modular.com [Source type: Reference]

^ See Differential GPS A technique to improve position accuracy by supplying pseudorange corrections transmitted by a Beacon close to the GPS receiver.
  • Micro Modular Technologies - GPS and Wireless Modules - Support 27 January 2010 23:56 UTC www.micro-modular.com [Source type: Reference]

^ Real Time Kinematic (RTK) - The Differential GPS procedure whereby carrier phase corrections are transmitted in real time from a reference station to the user's roving receiver.
  • Micro Modular Technologies - GPS and Wireless Modules - Support 27 January 2010 23:56 UTC www.micro-modular.com [Source type: Reference]

.As the distance increases, the errors at the two sites will not correlate as well, resulting in less precise differential corrections.^ Ephemeris errors can be removed by differential correction.
  • Micro Modular Technologies - GPS and Wireless Modules - Support 27 January 2010 23:56 UTC www.micro-modular.com [Source type: Reference]

^ A base station calculates the error for each satellite, improving the accuracy of GPS positions collected at unknown locations by a roving GPS receiver through differential correction.
  • Micro Modular Technologies - GPS and Wireless Modules - Support 27 January 2010 23:56 UTC www.micro-modular.com [Source type: Reference]

.During the 1990-91 Gulf War, the shortage of military GPS units caused many troops and their families to buy readily available civilian units.^ During the 1990-91 Gulf War , the shortage of military GPS units and the ready availability of civilian ones caused many troops to buy their own civilian GPS units: their wide use among personnel resulted in a decision to disable Selective Availability.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ Many civilian applications benefit from GPS signals, using one or more of three basic components of the GPS: absolute location, relative movement, and time transfer.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ This was ironic, as SA had been introduced specifically for these situations, allowing friendly troops to use the signal for accurate navigation, while at the same time denying it to the enemy—but the assumption underlying this policy was that all U.S. troops and enemy troops would have military-specification GPS receivers and that civilian receivers would not exist in war zones.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

.This significantly impeded the U.S. military's own battlefield use of GPS, so the military made the decision to turn off SA for the duration of the war.^ During the 1990-91 Gulf War , the shortage of military GPS units and the ready availability of civilian ones caused many troops to buy their own civilian GPS units: their wide use among personnel resulted in a decision to disable Selective Availability.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ This was ironic, as SA had been introduced specifically for these situations, allowing friendly troops to use the signal for accurate navigation, while at the same time denying it to the enemy—but the assumption underlying this policy was that all U.S. troops and enemy troops would have military-specification GPS receivers and that civilian receivers would not exist in war zones.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ P-Code- The precise code of the GPS signal typically used only by the U.S. military.
  • Micro Modular Technologies - GPS and Wireless Modules - Support 27 January 2010 23:56 UTC www.micro-modular.com [Source type: Reference]

.In the 1990s, the FAA started pressuring the military to turn off SA permanently.^ In the 1990s, the FAA started pressuring the military to turn off SA permanently.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ After SA, which has been turned off, the largest error in GPS is usually the unpredictable delay through the ionosphere.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ SA has been turned off since 2000 by presidential order.
  • Micro Modular Technologies - GPS and Wireless Modules - Support 27 January 2010 23:56 UTC www.micro-modular.com [Source type: Reference]

.This would save the FAA millions of dollars every year in maintenance of their own radio navigation systems.^ This would save the FAA millions of dollars every year in maintenance of their own radio navigation systems.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ In the 1970s, the ground-based Omega Navigation System , based on signal phase comparison, became the first worldwide radio navigation system.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ The week number is transmitted as a ten- bit field in the C/A and P(Y) navigation messages, and so it becomes zero again every 1,024 weeks (19.6 years).
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

.The amount of error added was "set to zero"[63] at midnight on May 1, 2000 following an announcement by U.S. President Bill Clinton, allowing users access to the error-free L1 signal.^ The amount of error added was "set to zero"at midnight on May 1, 2000 following an announcement by U.S. President Bill Clinton , allowing users access to the error-free L1 signal.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ In 1996, recognizing the importance of GPS to civilian users as well as military users, U.S. President Bill Clinton issued a policy directive ] declaring GPS to be a dual-use system and establishing an Interagency GPS Executive Board to manage it as a national asset.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ It allows a direct comparison of the L1 and L2 signals using the coded signal instead of the carrier wave.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

Per the directive, the induced error of SA was changed to add no error to the public signals (C/A code). .Clinton's executive order required SA to be set to zero by 2006; it happened in 2000 once the U.S. military developed a new system that provides the ability to deny GPS (and other navigation services) to hostile forces in a specific area of crisis without affecting the rest of the world or its own military systems.^ Clinton's executive order required SA to be set to zero by 2006; it happened in 2000 once the US military developed a new system that provides the ability to deny GPS (and other navigation services) to hostile forces in a specific area of crisis without affecting the rest of the world or its own military systems.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ HTC Touch Accessories In Car GPS systems TomTom GPS items as GPS navigation software now New TomTom Sat Nav Tomtom Go One Cheap .
  • GPS. GPS Software, Palm GPS. Pocket pc GPS. Handheld gps. GPS navigation 13 January 2010 11:56 UTC gps.pdatopsoft.com [Source type: Academic]

^ Bradford Parkinson , professor of aeronautics and astronautics at Stanford University , conceived the present satellite-based system in the early 1960s and developed it in conjunction with the U.S. Air Force.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

[63]
.Selective Availability is still a system capability of GPS, and could, in theory, be reintroduced at any time.^ Selective Availability is still a system capability of GPS, and error could, in theory, be reintroduced at any time.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ GPS (Global Positioning System) is one of the technical marvels of our time.
  • Global Positioning System 27 January 2010 23:56 UTC michna.com [Source type: FILTERED WITH BAYES]

^ On May 1st, 2000, the US made a surprise move and switched off the dreaded Selective Availability (SA) distortion of the GPS sattelite signals.
  • Global Positioning System 27 January 2010 23:56 UTC michna.com [Source type: FILTERED WITH BAYES]

.In practice, in view of the hazards and costs this would induce for U.S. and foreign shipping, it is unlikely to be reintroduced, and various government agencies, including the FAA,[64] have stated that it is not intended to be reintroduced.^ In practice, in view of the hazards and costs this would induce for US and foreign shipping, it is unlikely to be reintroduced, and various government agencies, including the FAA , have stated that it is not intended to be reintroduced.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ It shipped and the cost of returning would be more than the value of the case.
  • Garmin 3.5Inch Carrying Case | Ultra Gps 16 January 2010 16:26 UTC ultra-gps.com [Source type: FILTERED WITH BAYES]

.One interesting side effect of the Selective Availability hardware is the capability to add corrections to the outgoing signal of the GPS cesium and rubidium atomic clocks to an accuracy of approximately 2 × 10−13 This represented a significant improvement over the raw accuracy of the clocks.^ GPS satellites contain multiple cesium and rubidium clocks.
  • Micro Modular Technologies - GPS and Wireless Modules - Support 27 January 2010 23:56 UTC www.micro-modular.com [Source type: Reference]

^ See Radio Technical Commission For Maritime Services See Real Time Kinematic See Selective Availability A system designed to improve the accuracy of GPS using ground stations to monitor the GPS signals, calculate corrections, and then transmit them from satellites to the GPS receiver.
  • Micro Modular Technologies - GPS and Wireless Modules - Support 27 January 2010 23:56 UTC www.micro-modular.com [Source type: Reference]

^ A precision clock that depends for its operation on an electrical oscillator regulated by the natural vibration frequencies of a beam of cesium or rubidium atoms.
  • Micro Modular Technologies - GPS and Wireless Modules - Support 27 January 2010 23:56 UTC www.micro-modular.com [Source type: Reference]

[citation needed]
.On 19 September 2007, the United States Department of Defense announced that future GPS III satellites will not be capable of implementing SA,[65] eventually making the policy permanent.^ On 19 September 2007, the United States Department of Defense announced that future GPS III satellites will not be capable of implementing SA,eventually making the policy permanent.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ The GPS satellites also carry a set of nuclear detonation detectors consisting of an optical sensor (Y-sensor), an X-ray sensor, a dosimeter, and an Electro-Magnetic Pulse (EMP) sensor (W-sensor) which form a major portion of the United States Nuclear Detonation Detection System .
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ WAAS consists of approximately 25 ground reference stations positioned across the United States that monitor GPS satellites.
  • Micro Modular Technologies - GPS and Wireless Modules - Support 27 January 2010 23:56 UTC www.micro-modular.com [Source type: Reference]

[66]

Relativity

Satellite clocks are slowed by their orbital speed but sped up by their distance out of the Earth's gravitational well.
.A number of sources of error exist due to relativistic effects [67] that would render the system useless if uncorrected.^ Atmospheric Effects in "Sources of Errors in GPS" ) .
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

Three relativistic effects are the time dilation, gravitational frequency shift, and eccentricity effects. .For example, the relativistic time slowing due to the speed of the satellite of about 1 part in 1010, the gravitational time dilation that makes a satellite run about 5 parts in 1010 faster than an Earth based clock, and the Sagnac effect due to rotation relative to receivers on Earth.^ The difference between the clock time maintained in the GPS receiver and GPS satellite time.
  • Micro Modular Technologies - GPS and Wireless Modules - Support 27 January 2010 23:56 UTC www.micro-modular.com [Source type: Reference]

^ Satellite clocks are slowed by their orbital speed but sped up by their distance out of the earth's gravitational well.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ A specific orbit where a satellite rotates around the earth at the same rotational speed as the earth.
  • Micro Modular Technologies - GPS and Wireless Modules - Support 27 January 2010 23:56 UTC www.micro-modular.com [Source type: Reference]

These topics are examined below, one at a time.

Special and general relativity

.According to the theory of relativity, due to their constant movement and height relative to the Earth-centered, non-rotating approximately inertial reference frame, the clocks on the satellites are affected by their speed.^ According to the theory of relativity , due to their constant movement and height relative to the Earth-centered inertial reference frame , the clocks on the satellites are affected by their speed ( special relativity ) as well as their gravitational potential ( general relativity ).
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ A specific orbit where a satellite rotates around the earth at the same rotational speed as the earth.
  • Micro Modular Technologies - GPS and Wireless Modules - Support 27 January 2010 23:56 UTC www.micro-modular.com [Source type: Reference]

^ The six planes have approximately 55° inclination (tilt relative to Earth's equator ) and are separated by 60° right ascension of the ascending node (angle along the equator from a reference point to the orbit's intersection).The orbits are arranged so that at least six satellites are always within line of sight from almost everywhere on Earth's surface.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

.Special relativity predicts that the frequency of the atomic clocks moving at GPS orbital speeds will tick more slowly than stationary ground clocks by a factor of \frac{v^{2}}{2c^{2}}\approx 10 ^{-10}, or result in a delay of about 7 μs/day, where the orbital velocity is v = 4 km/s, and c = the speed of light.^ A change in the observed frequency of a wave, occurring when the receiver and transmitter are in motion relative to each other, with the frequency increasing when the source and observer approach each other and decreasing when they move apart.
  • Micro Modular Technologies - GPS and Wireless Modules - Support 27 January 2010 23:56 UTC www.micro-modular.com [Source type: Reference]

^ If you have more height than you need, move the final approach fix out to, say, 2 nm from the field.
  • Global Positioning System 27 January 2010 23:56 UTC michna.com [Source type: FILTERED WITH BAYES]

^ Multi-channel receiver- A GPS receiver which can simultaneously track more than one satellite signal.
  • Micro Modular Technologies - GPS and Wireless Modules - Support 27 January 2010 23:56 UTC www.micro-modular.com [Source type: Reference]

.The time dilation effect has been measured and verified using the GPS system.^ Doppler Aiding- A signal processing strategy that uses a measured doppler shift to help the receiver smoothly track the GPS signal.
  • Micro Modular Technologies - GPS and Wireless Modules - Support 27 January 2010 23:56 UTC www.micro-modular.com [Source type: Reference]

^ GPS (Global Positioning System) is one of the technical marvels of our time.
  • Global Positioning System 27 January 2010 23:56 UTC michna.com [Source type: FILTERED WITH BAYES]

^ A signal processing strategy that uses the GPS carrier phase to augment the measured code phase for better accuracy.
  • Micro Modular Technologies - GPS and Wireless Modules - Support 27 January 2010 23:56 UTC www.micro-modular.com [Source type: Reference]

.The effect of gravitational frequency shift on the GPS system due to general relativity is that a clock closer to a massive object will be slower than a clock farther away.^ The apparent propagation time is determined from the time shift required to align a replica of the GPS code generated in the receiver with the received GPS code.
  • Micro Modular Technologies - GPS and Wireless Modules - Support 27 January 2010 23:56 UTC www.micro-modular.com [Source type: Reference]

^ Spread Spectrum- In GPS the L-band signal is spread over a frequency band much wider than the minimum bandwidth needed to transmit the information being sent.
  • Micro Modular Technologies - GPS and Wireless Modules - Support 27 January 2010 23:56 UTC www.micro-modular.com [Source type: Reference]

^ In GPS the L-band signal is spread over a frequency band much wider than the minimum bandwidth needed to transmit the information being sent.
  • Micro Modular Technologies - GPS and Wireless Modules - Support 27 January 2010 23:56 UTC www.micro-modular.com [Source type: Reference]

.Applied to the GPS system, the receivers are much closer to Earth than the satellites, causing the GPS clocks to be faster by a factor of 5×10^(-10), or about 45.9 μs/day.^ Correcting a GPS receiver's clock .
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

^ The difference between the clock time maintained in the GPS receiver and GPS satellite time.
  • Micro Modular Technologies - GPS and Wireless Modules - Support 27 January 2010 23:56 UTC www.micro-modular.com [Source type: Reference]

^ To account for this, the frequency standard on board each satellite is given a rate offset prior to launch, making it run slightly slower than the desired frequency on Earth; specifically, at 10.22999999543 MHz instead of 10.23 MHz.
  • Global Positioning System - a knol by Siddhant jain 27 January 2010 23:56 UTC knol.google.com [Source type: FILTERED WITH BAYES]

This gravitational frequency shift is also a noticeable effect.
When combining the time dilation and gravitational frequency shift, the discrepancy is about 38 microseconds per day; a difference of 4.465 parts in 1010.[68] .Without correction, errors in position determination of roughly 10 km/day would accumulate.^ They said they would correct the error, but made no offer to exchange for the correct item or make any other adjustment.
  • Garmin 3.5Inch Carrying Case | Ultra Gps 16 January 2010 16:26 UTC ultra-gps.com [Source type: FILTERED WITH BAYES]

^ The altitude error remains bigger than the position error by a factor of roughly 1.5 but has now become usable for many more purposes for which it was too imprecise in the days of SA. There are no plans to switch SA back on.
  • Global Positioning System 27 January 2010 23:56 UTC michna.com [Source type: FILTERED WITH BAYES]

^ A base station calculates the error for each satellite, improving the accuracy of GPS positions collected at unknown locations by a roving GPS receiver through differential correction.
  • Micro Modular Technologies - GPS and Wireless Modules - Support 27 January 2010 23:56 UTC www.micro-modular.com [Source type: Reference]

.In addition, because GPS satellite orbits are not perfectly circular, their elliptical orbits cause the time dilation and gravitational frequency shift effects to vary with time.^ Constellation- The set of GPS satellites in orbit.
  • Micro Modular Technologies - GPS and Wireless Modules - Support 27 January 2010 23:56 UTC www.micro-modular.com [Source type: Reference]

^ A satellite in geosynchronous orbit appears to remain at a fixed longitude (but its latitude may vary) .
  • Micro Modular Technologies - GPS and Wireless Modules - Support 27 January 2010 23:56 UTC www.micro-modular.com [Source type: Reference]

^ L2 Frequency- One of the carrier frequencies transmitted by the GPS satellites.
  • Micro Modular Technologies - GPS and Wireless Modules - Support 27 January 2010 23:56 UTC www.micro-modular.com [Source type: Reference]

This eccentricity effect causes the clock rate difference between a GPS satellite and a receiver to increase or decrease depending on the velocity orbital altitude of the satellite.
.To account for the discrepancy, the frequency standard on board each satellite is given a rate offset prior to launch, making it run slightly slower than the desired frequency on Earth; specifically, at 10.22999999543 MHz instead of 10.23 MHz.^ If you clicked on your desired emergency destination, then on Go To, and see that your required sink rate to destination is lower than your actual sink rate, you know you won't make it, so you have to do something.
  • Global Positioning System 27 January 2010 23:56 UTC michna.com [Source type: FILTERED WITH BAYES]

^ A specific orbit where a satellite rotates around the earth at the same rotational speed as the earth.
  • Micro Modular Technologies - GPS and Wireless Modules - Support 27 January 2010 23:56 UTC www.micro-modular.com [Source type: Reference]

^ Geosynchronous Orbit- A specific orbit where a satellite rotates around the earth at the same rotational speed as the earth.
  • Micro Modular Technologies - GPS and Wireless Modules - Support 27 January 2010 23:56 UTC www.micro-modular.com [Source type: Reference]

[69] .Since the atomic clocks on board the GPS satellites are precisely tuned, it makes the system a practical engineering application of the scientific theory of relativity in a real-world environment.^ GPS satellites contain multiple cesium and rubidium clocks.
  • Micro Modular Technologies - GPS and Wireless Modules - Support 27 January 2010 23:56 UTC www.micro-modular.com [Source type: Reference]

^ Clock Bias- The difference between the clock time maintained in the GPS receiver and GPS satellite time.
  • Micro Modular Technologies - GPS and Wireless Modules - Support 27 January 2010 23:56 UTC www.micro-modular.com [Source type: Reference]

^ Local Area Augmentation System (LAAS) - The FAA system of short range ground-based Differential GPS to support precision instrument approaches of aircraft.
  • Micro Modular Technologies - GPS and Wireless Modules - Support 27 January 2010 23:56 UTC www.micro-modular.com [Source type: Reference]

[70] Placing atomic clocks on artificial satellites to test Einstein's general theory was proposed by Friedwardt Winterberg in 1955.[71]

Sagnac distortion

GPS observation processing must also compensate for the Sagnac effect. .The GPS time scale is defined in an inertial system but observations are processed in an Earth-centered, Earth-fixed (co-rotating) system, a system in which simultaneity is not uniquely defined.^ GPS (Global Positioning System) is one of the technical marvels of our time.
  • Global Positioning System 27 January 2010 23:56 UTC michna.com [Source type: FILTERED WITH BAYES]

^ UTC is corrected by adding (or subtracting) leap seconds as required to match solar time (which is based on the Earth's rotation).
  • Micro Modular Technologies - GPS and Wireless Modules - Support 27 January 2010 23:56 UTC www.micro-modular.com [Source type: Reference]

^ See Velocity Made Good See Wide Area Augmentation System The start mode in which a GPS receiver has its position and approximate time available but not ephemeris data.
  • Micro Modular Technologies - GPS and Wireless Modules - Support 27 January 2010 23:56 UTC www.micro-modular.com [Source type: Reference]

A Lorentz transformation is thus applied to convert from the inertial system to the ECEF system. .The resulting signal run time correction has opposite algebraic signs for satellites in the Eastern and Western celestial hemispheres.^ It includes system time, clock correction parameters, ionospheric delay model parameters, the satellite's ephemeris data and health plus almanac data for all satellites.
  • Micro Modular Technologies - GPS and Wireless Modules - Support 27 January 2010 23:56 UTC www.micro-modular.com [Source type: Reference]

^ Satellite Based Augmentation System (SBAS) - A system designed to improve the accuracy of GPS using ground stations to monitor the GPS signals, calculate corrections, and then transmit them from satellites to the GPS receiver.
  • Micro Modular Technologies - GPS and Wireless Modules - Support 27 January 2010 23:56 UTC www.micro-modular.com [Source type: Reference]

^ Acquisition Time- Period required by a GPS receiver to determine initial position based on acquisition of satellite signals.
  • Micro Modular Technologies - GPS and Wireless Modules - Support 27 January 2010 23:56 UTC www.micro-modular.com [Source type: Reference]

.Ignoring this effect will produce an east-west error on the order of hundreds of nanoseconds, or tens of meters in position.^ The datum selected on a GPS receiver must match the datum listed on the corresponding paper map or errors of hundreds of meters can result.
  • Micro Modular Technologies - GPS and Wireless Modules - Support 27 January 2010 23:56 UTC www.micro-modular.com [Source type: Reference]

[72]

Natural sources of interference

.Since GPS signals at terrestrial receivers tend to be relatively weak, natural radio signals or scattering of the GPS signals can desensitize the receiver, making acquiring and tracking the satellite signals difficult or impossible.^ Accurate measurement of the relative positions of two receivers tracking the same GPS signals.
  • Micro Modular Technologies - GPS and Wireless Modules - Support 27 January 2010 23:56 UTC www.micro-modular.com [Source type: Reference]

^ A GPS receiver which can simultaneously track more than one satellite signal.
  • Micro Modular Technologies - GPS and Wireless Modules - Support 27 January 2010 23:56 UTC www.micro-modular.com [Source type: Reference]

^ Cycle slip- A discontinuity of an interger number of cycles in the measured carrier phase due to a temporary loss-of-lock in the carrier tracking loop of a GPS receiver.
  • Micro Modular Technologies - GPS and Wireless Modules - Support 27 January 2010 23:56 UTC www.micro-modular.com [Source type: Reference]

Space weather degrades GPS operation in two ways, direct interference by solar radio burst noise in the same frequency band[73] or by scattering of the GPS radio signal in ionospheric irregularities referred to as scintillation.[74] Both forms of degradation follow the 11 year solar cycle and are a maximum at sunspot maximum although they can occur at anytime. Solar radio bursts are associated with solar flares and their impact can affect reception over the half of the Earth facing the sun. Scintillation occurs most frequently at tropical latitudes where it is a night time phenomenon. It occurs less frequently at high latitudes or mid-latitudes where magnetic storms can lead to scintillation.[75] In addition to producing scintillation, magnetic storms can produce strong ionospheric gradients that degrade the accuracy of SBAS systems.[76]

Artificial sources of interference

In automotive GPS receivers, metallic features in windshields,[77] such as defrosters, or car window tinting films[78] can act as a Faraday cage, degrading reception just inside the car.
Man-made EMI (electromagnetic interference) can also disrupt, or jam, GPS signals. .In one well documented case, the entire harbor of Moss Landing, California was unable to receive GPS signals due to unintentional jamming caused by malfunctioning TV antenna preamplifiers.^ Perhaps a “belt loop” would have been nice, but if you are looking for a case to protect your GPS when you put it in a purse or glove compartment this one will do the job.
  • Garmin 3.5Inch Carrying Case | Ultra Gps 16 January 2010 16:26 UTC ultra-gps.com [Source type: FILTERED WITH BAYES]

^ Rating:5 out of 5 stars The case is a “must” to protect your GPS and this one is a nice, small, well-made one.
  • Garmin 3.5Inch Carrying Case | Ultra Gps 16 January 2010 16:26 UTC ultra-gps.com [Source type: FILTERED WITH BAYES]

^ Nice Rating:5 out of 5 stars I think this case is so necessary because it protects the GPS windows so well.
  • Garmin 3.5Inch Carrying Case | Ultra Gps 16 January 2010 16:26 UTC ultra-gps.com [Source type: FILTERED WITH BAYES]

[79][80] Intentional jamming is also possible. Generally, stronger signals can interfere with GPS receivers when they are within radio range, or line of sight. In 2002, a detailed description of how to build a short range GPS L1 C/A jammer was published in the online magazine Phrack.[81]
.The U.S. government believes that such jammers were used occasionally during the 2001 war in Afghanistan and the U.S. military claimed to destroy six GPS jammers during the Iraq War, including one that was destroyed ironically with a GPS-guided bomb.^ After more than one years use, the gps looks brand new.
  • Garmin 3.5Inch Carrying Case | Ultra Gps 16 January 2010 16:26 UTC ultra-gps.com [Source type: FILTERED WITH BAYES]

^ While I love the GPS, and think I definitely could use a case for it, I’m not completely sure this is the best one for the job.
  • Garmin 3.5Inch Carrying Case | Ultra Gps 16 January 2010 16:26 UTC ultra-gps.com [Source type: FILTERED WITH BAYES]

[82] Such a jammer is relatively easy to detect and locate, making it an attractive target for anti-radiation missiles. The UK Ministry of Defence tested a jamming system in the UK's West Country on 7 and 8 June 2007.[83]
.Some countries allow the use of GPS repeaters to allow for the reception of GPS signals indoors and in obscured locations, however, under EU and UK laws, the use of these is prohibited as the signals can cause interference to other GPS receivers that may receive data from both GPS satellites and the repeater.^ Basic and simple to use Rating:3 out of 5 stars This case is easy to use but may be a little short for the 4″ wide GPS systems as they stick out a bit.
  • Garmin 3.5Inch Carrying Case | Ultra Gps 16 January 2010 16:26 UTC ultra-gps.com [Source type: FILTERED WITH BAYES]

Due to the potential for both natural and man-made noise, numerous techniques continue to be developed to deal with the interference. The first is to not rely on GPS as a sole source. According to John Ruley, "IFR pilots should have a fallback plan in case of a GPS malfunction".[84] Receiver Autonomous Integrity Monitoring (RAIM) is a feature now included in some receivers, which is designed to provide a warning to the user if jamming or another problem is detected. The U.S. military has also deployed their Selective Availability / Anti-Spoofing Module (SAASM) in the Defense Advanced GPS Receiver (DAGR). In demonstration videos, the DAGR is able to detect jamming and maintain its lock on the encrypted GPS signals during interference which causes civilian receivers to lose lock.[85]

Accuracy enhancement and surveying

Augmentation

Augmentation methods of improving accuracy rely on external information being integrated into the calculation process. There are many such systems in place and they are generally named or described based on how the GPS sensor receives the information. Some systems transmit additional information about sources of error (such as clock drift, ephemeris, or ionospheric delay), others provide direct measurements of how much the signal was off in the past, while a third group provide additional navigational or vehicle information to be integrated in the calculation process.
.Examples of augmentation systems include the Wide Area Augmentation System, Differential GPS, Inertial Navigation Systems and Assisted GPS.^ Basic and simple to use Rating:3 out of 5 stars This case is easy to use but may be a little short for the 4″ wide GPS systems as they stick out a bit.
  • Garmin 3.5Inch Carrying Case | Ultra Gps 16 January 2010 16:26 UTC ultra-gps.com [Source type: FILTERED WITH BAYES]

Precise monitoring

The accuracy of a calculation can also be improved through precise monitoring and measuring of the existing GPS signals in additional or alternate ways.
After SA, which has been turned off, the largest error in GPS is usually the unpredictable delay through the ionosphere. The spacecraft broadcast ionospheric model parameters, but errors remain. .This is one reason the GPS spacecraft transmit on at least two frequencies, L1 and L2. Ionospheric delay is a well-defined function of frequency and the total electron content (TEC) along the path, so measuring the arrival time difference between the frequencies determines TEC and thus the precise ionospheric delay at each frequency.^ Rating:5 out of 5 stars The case is a “must” to protect your GPS and this one is a nice, small, well-made one.
  • Garmin 3.5Inch Carrying Case | Ultra Gps 16 January 2010 16:26 UTC ultra-gps.com [Source type: FILTERED WITH BAYES]

Receivers with decryption keys can decode the P(Y)-code transmitted on both L1 and L2. However, these keys are reserved for the military and authorized agencies and are not available to the public. Without keys, it is still possible to use a codeless technique to compare the P(Y) codes on L1 and L2 to gain much of the same error information. However, this technique is slow, so it is currently limited to specialized surveying equipment. In the future, additional civilian codes are expected to be transmitted on the L2 and L5 frequencies (see GPS modernization). Then all users will be able to perform dual-frequency measurements and directly compute ionospheric delay errors.
A second form of precise monitoring is called Carrier-Phase Enhancement (CPGPS). The error, which this corrects, arises because the pulse transition of the PRN is not instantaneous, and thus the correlation (satellite-receiver sequence matching) operation is imperfect. The CPGPS approach utilizes the L1 carrier wave, which has a period of  \frac{1 sec}{1575.42 * 10^6} = 0.63475 \ nanoseconds \approx 1 \ nanosecond \ which is about one-thousandth of the C/A Gold code bit period of  \frac{1 sec}{1023 * 10^3} = 977.5 \ nanosecond \ \approx 1000 \ nanosecond \ , to act as an additional clock signal and resolve the uncertainty. The phase difference error in the normal GPS amounts to between 2 and 3 meters (6 to 10 ft) of ambiguity. CPGPS working to within 1% of perfect transition reduces this error to 3 centimeters (1 inch) of ambiguity. By eliminating this source of error, CPGPS coupled with DGPS normally realizes between 20 and 30 centimeters (8 to 12 inches) of absolute accuracy.
Relative Kinematic Positioning (RKP) is another approach for a precise GPS-based positioning system. In this approach, determination of range signal can be resolved to a precision of less than 10 centimeters (4 in). This is done by resolving the number of cycles in which the signal is transmitted and received by the receiver. .This can be accomplished by using a combination of differential GPS (DGPS) correction data, transmitting GPS signal phase information and ambiguity resolution techniques via statistical tests—possibly with processing in real-time (real-time kinematic positioning, RTK).^ Really useful to keep your GPS protected.
  • Garmin 3.5Inch Carrying Case | Ultra Gps 16 January 2010 16:26 UTC ultra-gps.com [Source type: FILTERED WITH BAYES]

Timekeeping

While most clocks are synchronized to Coordinated Universal Time (UTC), the atomic clocks on the satellites are set to GPS time. The difference is that GPS time is not corrected to match the rotation of the Earth, so it does not contain leap seconds or other corrections which are periodically added to UTC. GPS time was set to match Coordinated Universal Time (UTC) in 1980, but has since diverged. The lack of corrections means that GPS time remains at a constant offset with International Atomic Time (TAI) (TAI - GPS = 19 seconds). Periodic corrections are performed on the on-board clocks to correct relativistic effects and keep them synchronized with ground clocks.
The GPS navigation message includes the difference between GPS time and UTC, which as of 2009 is 15 seconds due to the leap second added to UTC December 31, 2008. Receivers subtract this offset from GPS time to calculate UTC and specific timezone values. .New GPS units may not show the correct UTC time until after receiving the UTC offset message.^ So within a week’s time I received my new case from Garmin.
  • Garmin 3.5Inch Carrying Case | Ultra Gps 16 January 2010 16:26 UTC ultra-gps.com [Source type: FILTERED WITH BAYES]

The GPS-UTC offset field can accommodate 255 leap seconds (eight bits) which, given the current rate of change of the Earth's rotation (with one leap second introduced approximately every 18 months), should be sufficient to last until approximately the year 2300.
As opposed to the year, month, and day format of the Gregorian calendar, the GPS date is expressed as a week number and a seconds-into-week number. The week number is transmitted as a ten-bit field in the C/A and P(Y) navigation messages, and so it becomes zero again every 1,024 weeks (19.6 years). GPS week zero started at 00:00:00 UTC (00:00:19 TAI) on January 6, 1980, and the week number became zero again for the first time at 23:59:47 UTC on August 21, 1999 (00:00:19 TAI on August 22, 1999). To determine the current Gregorian date, a GPS receiver must be provided with the approximate date (to within 3,584 days) to correctly translate the GPS date signal. .To address this concern the modernized GPS navigation message uses a 13-bit field, which only repeats every 8,192 weeks (157 years), thus lasting until the year 2137 (157 years after GPS week zero).^ Basic and simple to use Rating:3 out of 5 stars This case is easy to use but may be a little short for the 4″ wide GPS systems as they stick out a bit.
  • Garmin 3.5Inch Carrying Case | Ultra Gps 16 January 2010 16:26 UTC ultra-gps.com [Source type: FILTERED WITH BAYES]

^ After more than one years use, the gps looks brand new.
  • Garmin 3.5Inch Carrying Case | Ultra Gps 16 January 2010 16:26 UTC ultra-gps.com [Source type: FILTERED WITH BAYES]

^ At the same time, Amazon refuses to recognize my rural address, which I’ve been using for more than 18 years.
  • Garmin 3.5Inch Carrying Case | Ultra Gps 16 January 2010 16:26 UTC ultra-gps.com [Source type: FILTERED WITH BAYES]

Carrier phase tracking (surveying)

Utilizing the navigation message to measure pseudorange has been discussed. .Another method that is used in GPS surveying applications is carrier phase tracking.^ If you always carry your GPS with the open end of the case between parallel and vertical to the ground, this is a gorgeous useful case.
  • Garmin 3.5Inch Carrying Case | Ultra Gps 16 January 2010 16:26 UTC ultra-gps.com [Source type: FILTERED WITH BAYES]

^ Carrying Case Not for Me Rating:2 out of 5 stars Since my GPS will pretty much stay in my car, this won’t be too useful for me.
  • Garmin 3.5Inch Carrying Case | Ultra Gps 16 January 2010 16:26 UTC ultra-gps.com [Source type: FILTERED WITH BAYES]

The period of the carrier frequency times the speed of light gives the wave length, which is about 0.19 meters for the L1 carrier. With a 1% of wave length accuracy in detecting the leading edge, this component of pseudorange error might be as low as 2 millimeters. This compares to 3 meters for the C/A code and 0.3 meters for the P code.
However, this 2 millimeter accuracy requires measuring the total phase, that is the total number of wave lengths plus the fractional wavelength. This requires specially equipped receivers. This method has many applications in the field of surveying.
We now describe a method which could potentially be used to estimate the position of receiver 2 given the position of receiver 1 using triple differencing followed by numerical root finding, and a mathematical technique called least squares. A detailed discussion of the errors is omitted in order to avoid detracting from the description of the methodology. In this description differences are taken in the order of differencing between satellites, differencing between receivers, and differencing between epochs. .This should not be construed to mean that this is the only order which can be used.^ Should Be Included With Purchase Rating:5 out of 5 stars This is a great case to have in order to protect the gps screen when not in use.
  • Garmin 3.5Inch Carrying Case | Ultra Gps 16 January 2010 16:26 UTC ultra-gps.com [Source type: FILTERED WITH BAYES]

Indeed other orders of taking differences are equally valid.
The satellite carrier total phase can be measured with ambiguity as to the number of cycles as described in CARRIER PHASE MEASUREMENT and CARRIER BEAT PHASE. Let \ \phi(r_i, s_j, t_k) denote the phase of the carrier of satellite j measured by receiver i at time \ \ t_k . This notation has been chosen so as to make it clear what the subscripts i, j, and k mean. In view of the fact that the receiver, satellite, and time come in alphabetical order as arguments of \ \phi and to strike a balance between readability and conciseness, let \ \phi_{i,j,k} = \phi(r_i, s_j, t_k) so as to have a concise abbreviation. Also we define three functions, :\ \Delta^r, \Delta^s, \Delta^t which perform differences between receivers, satellites, and time points respectively. Each of these functions has a linear combination of variables with three subscripts as its argument. These three functions are defined below. If \ \alpha_{i,j,k} is a function of the three integer arguments, i, j, and k then it is a valid argument for the functions, :\ \Delta^r, \Delta^s, \Delta^t , with the values defined as
\ \Delta^r(\alpha_{i,j,k}) = \alpha_{i+1,j,k} - \alpha_{i,j,k} ,
\ \Delta^s(\alpha_{i,j,k}) = \alpha_{i,j+1,k} - \alpha_{i,j,k} , and
\ \Delta^t(\alpha_{i,j,k}) = \alpha_{i,j,k+1} - \alpha_{i,j,k} .
Also if \ \alpha_{i,j,k}\ and\ \beta_{l,m,n} are valid arguments for the three functions and a and b are constants then \ ( a\ \alpha_{i,j,k} + b\ \beta_{l,m,n} ) is a valid argument with values defined as
\ \Delta^r(a\ \alpha_{i,j,k} + b\ \beta_{l,m,n}) = a \ \Delta^r(\alpha_{i,j,k}) + b \ \Delta^r(\beta_{l,m,n}) ,
\ \Delta^s(a\ \alpha_{i,j,k} + b\ \beta_{l,m,n} )= a \ \Delta^s(\alpha_{i,j,k}) + b \ \Delta^s(\beta_{l,m,n}) , and
\ \Delta^t(a\ \alpha_{i,j,k} + b\ \beta_{l,m,n} )= a \ \Delta^t(\alpha_{i,j,k}) + b \ \Delta^t(\beta_{l,m,n}) .
Receiver clock errors can be approximately eliminated by differencing the phases measured from satellite 1 with that from satellite 2 at the same epoch as shown in BETWEEN-SATELLITE DIFFERENCING. This difference is designated as \ \Delta^s(\phi_{1,1,1}) = \phi_{1,2,1} - \phi_{1,1,1}
Double differencing can be performed by taking the differences of the between satellite difference observed by receiver 1 with that observed by receiver 2. The satellite clock errors will be approximately eliminated by this between receiver differencing. This double difference is:
\begin{align} \Delta^r(\Delta^s(\phi_{1,1,1}))\,&=\,\Delta^r(\phi_{1,2,1} - \phi_{1,1,1}) &=\,\Delta^r(\phi_{1,2,1}) - \Delta^r(\phi_{1,1,1}) &=\,(\phi_{2,2,1} - \phi_{1,2,1}) - (\phi_{2,1,1} - \phi_{1,1,1}) \end{align}
Triple differencing can be performed by taking the difference of double differencing performed at time \ \ t_2 with that performed at time \ \ t_1 . This will eliminate the ambiguity associated with the integral number of wave lengths in carrier phase provided this ambiguity does not change with time. Thus the triple difference result has eliminated all or practically all clock bias errors and the integer ambiguity. Also errors associated with atmospheric delay and satellite ephemeris have been significantly reduced. This triple difference is:
\ \Delta^t(\Delta^r(\Delta^s(\phi_{1,1,1})))
Triple difference results can be used to estimate unknown variables. For example if the position of receiver 1 is known but the position of receiver 2 unknown, it may be possible to estimate the position of receiver 2 using numerical root finding and least squares. Triple difference results for three independent time pairs quite possibly will be sufficient to solve for the three components of position of receiver 2. This may require the use of a numerical procedure such as one of those found in the chapter on root finding and nonlinear sets of equations in Numerical Recipes.[48] Also see Preview of Root Finding. To use such a numerical method, an initial approximation of the position of receiver 2 is required. This initial value could probably be provided by a position approximation based on the navigation message and the intersection of sphere surfaces. Although multidimensional numerical root finding can have problems, this disadvantage may be overcome with this good initial estimate. This procedure using three time pairs and a fairly good initial value followed by iteration will result in one observed triple difference result for receiver 2 position. Greater accuracy may be obtained by processing triple difference results for additional sets of three independent time pairs. This will result in an over determined system with multiple solutions. To get estimates for an over determined system, least squares can be used. The least squares procedure determines the position of receiver 2 which best fits the observed triple difference results for receiver 2 positions under the criterion of minimizing the sum of the squares.

Applications

The Global Positioning System, while originally a military project, is considered a dual-use technology, meaning it has significant applications for both the military and the civilian industry.

Military

The military applications of GPS span many purposes:
  • Navigation: GPS allows soldiers to find objectives in the dark or in unfamiliar territory, and to coordinate the movement of troops and supplies. The GPS-receivers that commanders and soldiers use are respectively called the Commanders Digital Assistant and the Soldier Digital Assistant.[86][87][88][89]
  • Target tracking: Various military weapons systems use GPS to track potential ground and air targets before they are flagged as hostile.[citation needed] These weapon systems pass GPS co-ordinates of targets to precision-guided munitions to allow them to engage the targets accurately. Military aircraft, particularly those used in air-to-ground roles use GPS to find targets (for example, gun camera video from AH-1 Cobras in Iraq show GPS co-ordinates that can be looked up in Google Earth).
  • Missile and projectile guidance: GPS allows accurate targeting of various military weapons including ICBMs, cruise missiles and precision-guided munitions. Artillery projectiles with embedded GPS receivers able to withstand accelerations of 12,000g's or about 117,600 meters/second2 have been developed for use in 155 mm howitzers.[90]
  • Search and Rescue: Downed pilots can be located faster if they have a GPS receiver.
  • Reconnaissance and Map Creation: The military use GPS extensively to aid mapping and reconnaissance.
  • The GPS satellites also carry a set of nuclear detonation detectors consisting of an optical sensor (Y-sensor), an X-ray sensor, a dosimeter, and an electromagnetic pulse (EMP) sensor (W-sensor) which form a major portion of the United States Nuclear Detonation Detection System.[91][92]

Civilian

This antenna is mounted on the roof of a hut containing a scientific experiment needing precise timing.
Many civilian applications benefit from GPS signals, using one or more of three basic components of the GPS: absolute location, relative movement, and time transfer.
The ability to determine the receiver's absolute location allows GPS receivers to perform as a surveying tool or as an aid to navigation. The capacity to determine relative movement enables a receiver to calculate local velocity and orientation, useful in vessels or observations of the Earth. Being able to synchronize clocks to exacting standards enables time transfer, which is critical in large communication and observation systems. An example is CDMA digital cellular. Each base station has a GPS timing receiver to synchronize its spreading codes with other base stations to facilitate inter-cell hand off and support hybrid GPS/CDMA positioning of mobiles for emergency calls and other applications. Finally, GPS enables researchers to explore the Earth environment including the atmosphere, ionosphere and gravity field. GPS survey equipment has revolutionized tectonics by directly measuring the motion of faults in earthquakes.
The U.S. Government controls the export of some civilian receivers. All GPS receivers capable of functioning above 18 km (60,000 ft) altitude and 515 m/s (1,000 knots) [93] are classified as munitions (weapons) for which U.S. State Department export licenses are required. These parameters are clearly chosen to prevent use of a receiver in a ballistic missile. It would not prevent use in a cruise missile since their altitudes and speeds are similar to those of ordinary aircraft.
This rule applies even to otherwise purely civilian units that only receive the L1 frequency and the C/A code and cannot correct for SA, etc.
Disabling operation above these limits exempts the receiver from classification as a munition. Different vendors have interpreted these limitations differently. The rule specifies operation above 18 km and 515 m/s, but some receivers stop operating at 18 km even when stationary. This has caused problems with some amateur radio balloon launches as they regularly reach 100,000 feet (30 km).
GPS tours are also an example of civilian use. The GPS is used to determine which content to display. For instance, when approaching a monument it would tell you about the monument.
GPS functionality has now started to move into mobile phones en masse. The first handsets with integrated GPS were launched already in the late 1990’s, and were available for broader consumer availability on networks such as those run by Nextel, Sprint and Verizon in 2002 in response to U.S. FCC mandates for handset positioning in emergency calls. Capabilities for access by third party software developers to these features were slower in coming, with Nextel opening up those APIs upon launch to any developer, Sprint following in 2006, and Verizon soon thereafter.
GPS Pet Tracking devices use the same network of satellites to pinpoint and transmit information about the whereabouts of a missing pet. These devices are normally attached to the collar of the pet and are to be worn at all times. A GPS pet tracking system will then offer 24/7 tracking of a pet’s location via mobile or Internet updates. GPS Pet Tracking Systems may use either radio waves or cell phones to transmit information and receive signals.[citation needed]

Awards

Two GPS developers received the National Academy of Engineering Charles Stark Draper Prize for 2003:
One GPS developer, Roger L. Easton, received the National Medal of Technology on February 13, 2006 at the White House.[94]
On February 10, 1993, the National Aeronautic Association selected the Global Positioning System Team as winners of the 1992 Robert J. Collier Trophy, the most prestigious aviation award in the United States. This team consists of researchers from the Naval Research Laboratory, the U.S. Air Force, the Aerospace Corporation, Rockwell International Corporation, and IBM Federal Systems Company. The citation accompanying the presentation of the trophy honors the GPS Team "for the most significant development for safe and efficient navigation and surveillance of air and spacecraft since the introduction of radio navigation 50 years ago."

Other systems

Other satellite navigation systems in use or various states of development include:

See also

Civilian applications

Related technologies

References

  1. ^ Astronautica Acta II, 25 (1956)
  2. ^ Jerry Proc. "Omega". Jproc.ca. http://www.jproc.ca/hyperbolic/omega.html. Retrieved 2009-12-08. 
  3. ^ "Why Did the Department of Defense Develop GPS?". Trimble Navigation Ltd. http://www.trimble.com/gps/whygps.shtml#0. Retrieved 2010-01-13. 
  4. ^ "Charting a Course Toward Global Navigation". The Aerospace Corporation. http://www.aero.org/publications/crosslink/summer2002/01.html. Retrieved 2010-01-14. 
  5. ^ "A Guide To The Global Positioning System (GPS) - GPS Timeline". Radio Shack. http://support.radioshack.com/support_tutorials/gps/gps_tmline.htm. Retrieved 2010-01-14. 
  6. ^ Michael Russell Rip, James M. Hasik (2002). The Precision Revolution: GPS and the Future of Aerial Warfare. Naval Institute Press. p. 65. ISBN 1557509735. http://books.google.com/books?id=mB9W3H90KDUC. Retrieved 2010-01-14. 
  7. ^ "ICAO Completes Fact-Finding Investigation". International Civil Aviation Organization. http://www.icao.int/cgi/goto_m.pl?icao/en/trivia/kal_flight_007.htm. Retrieved 2008-09-15. 
  8. ^ "United States Updates Global Positioning System Technology". America.gov. February 3, 2006. http://www.america.gov/xarchives/display.html?p=washfile-english&y=2006&m=February&x=20060203125928lcnirellep0.5061609. 
  9. ^ GPS Wing Reaches GPS III IBR Milestone in InsideGNSS November 10, 2008
  10. ^ Dietrich Schroeer, Mirco Elena (2000). Technology Transfer. Ashgate. p. 80. ISBN 075462045X. http://books.google.com/books?lr=&id=I7JRAAAAMAAJ. Retrieved 2008-05-25. 
  11. ^ Michael Russell Rip, James M. Hasik (2002). The Precision Revolution: GPS and the Future of Aerial Warfare. Naval Institute Press. ISBN 1557509735. http://books.google.com/books?lr=&id=_wpUAAAAMAAJ. Retrieved 2008-05-25. 
  12. ^ United States Department of Defense. Announcement of Initial Operational Capability Announcement of Initial Operational Capability at the Internet Archive. December 8, 1993.
  13. ^ National Archives and Records Administration. U.S. Global Positioning System Policy. March 29, 1996.
  14. ^ "3g.co.uk". 3g.co.uk. 2004-11-10. http://www.3g.co.uk/PR/November2004/8641.htm. Retrieved 2009-10-13. 
  15. ^ losangeles.af.mil
  16. ^ "United States Naval Observatory (USNO) GPS Constellation Status". ftp://tycho.usno.navy.mil/pub/gps/gpstd.txt. Retrieved 2009-10-13. 
  17. ^ United States Naval Observatory. GPS Constellation Status. Retrieved December 20, 2008.
  18. ^ Johnson, Bobbie (May 19, 2009). "GPS system 'close to breakdown'". The Guardian. http://www.guardian.co.uk/technology/2009/may/19/gps-close-to-breakdown. Retrieved 2009-12-08. 
  19. ^ Coursey, David (May 21, 2009). "Air Force Responds to GPS Outage Concerns". ABC News. http://abcnews.go.com/Technology/AheadoftheCurve/story?id=7647002&page=1. Retrieved 2009-05-22. 
  20. ^ GPS signals travel at the speed of light, so computing the distance for a given elapsed time is almost a straightforward calculation. However, the speed of light varies slightly between the partial vacuum of space and the atmosphere. A receiver can approximate these effects and produce a reasonable estimate. Once a rough position is determined, some receivers carefully compute the amount of atmosphere the signal traveled through and adjust the distance accordingly.
  21. ^ Georg zur Bonsen, Daniel Ammann, Michael Ammann, Etienne Favey, Pascal Flammant (2005-04-01). "Continuous Navigation Combining GPS with Sensor-Based Dead Reckoning". GPS World. http://www.gpsworld.com/gpsworld/article/articleDetail.jsp?id=154870&pageID=6. 
  22. ^ a b c d e "NAVSTAR GPS User Equipment Introduction" (PDF). US Government. http://www.navcen.uscg.gov/pubs/gps/gpsuser/gpsuser.pdf. 
  23. ^ "GPS Support Notes" (PDF). January 19, 2007. http://www.navmanwireless.com/uploads/EK/C8/EKC8zb1ITsNwDqWcqLQxiQ/Support_Notes_GPS_OperatingParameters.pdf. Retrieved 2008-11-10. 
  24. ^ It is also possible for a circle and a spherical surface to intersect at zero points, one point, or in the very special case in which the centers of the three spheres are colinear (i.e., all three on the same straight line) the sphere surface could intersect the entire circumference of the circle.
  25. ^ The two intersections are symmetrical about the plane containing the three satellites. Unless they are all in the same orbital plane, the plane containing them will not be a vertical one passing through the center of the Earth, and one intersection will be nearer the earth than the other.
  26. ^ John Pike. "GPS III Operational Control Segment (OCX)". Globalsecurity.org. http://www.globalsecurity.org/space/systems/gps_3-ocx.htm. Retrieved 2009-12-08. 
  27. ^ Daly, P.. "Navstar GPS and GLONASS: global satellite navigation systems". IEEE. http://ieeexplore.ieee.org/iel1/2219/7072/00285510.pdf?arnumber=285510. 
  28. ^ Dana, Peter H. (1996-08-08). "GPS Orbital Planes" (GIF). http://www.colorado.edu/geography/gcraft/notes/gps/gif/oplanes.gif. 
  29. ^ What the Global Positioning System Tells Us about Relativity. Retrieved January 2, 2007.
  30. ^ GPS Overview from the NAVSTAR Joint Program Office. Retrieved December 15, 2006.
  31. ^ "USCG Navcen: GPS Frequently Asked Questions". http://www.navcen.uscg.gov/faq/gpsfaq.htm. Retrieved 2007-01-31. 
  32. ^ Agnew, D.C. and Larson, K.M. (2007). "Finding the repeat times of the GPS constellation". GPS Solutions (Springer) 11 (1): 71–76. doi:10.1007/s10291-006-0038-4.  This article from author's web site, with minor correction.
  33. ^ Tis-pf-nisws. "Nanu 2008030". http://cgls.uscg.mil/pipermail/gps/2008-March/001625.html. 
  34. ^ Massatt, Paul; Wayne Brady (Summer 2002). "Optimizing performance through constellation management". Crosslink: 17–21. http://www.aero.org/publications/crosslink/summer2002/index.html. 
  35. ^ US Coast Guard General GPS News 9-9-05
  36. ^ USNO NAVSTAR Global Positioning System. Retrieved May 14, 2006.
  37. ^ Note that though there are many receiver manufacturers, they almost all use one of the chipsets produced for this purpose. An example: "GPS Receiver Chip Performance Survey". GPS Technology Reviews. http://gpstekreviews.com/2007/04/14/gps-receiver-chip-performance-survey/. 
  38. ^ NMEA NMEA 2000
  39. ^ "Publications and Standards from the National Marine Electronics Association (NMEA)". National Marine Electronics Association. http://www.nmea.org/pub/index.html. Retrieved 2008-06-27. 
  40. ^ "Interface Specification IS-GPS-200, Revision D: Navstar GPS Space Segment/Navigation User Interfaces" (PDF). Navstar GPS Joint Program Office. http://www.losangeles.af.mil/shared/media/document/AFD-070803-059.pdf.  Page 103.
  41. ^ How GPS works. Konowa.de (2005).
  42. ^ Fact Sheets - Global Positioning System. Los Angeles Air Force Base. August 2009.
  43. ^ "GPS Almanacs, NANUS, and Ops Advisories (including archives)". GPS Almanac Information. US Coast Guard. http://www.navcen.uscg.gov/gps/almanacs.htm. Retrieved 2009-09-09. 
  44. ^ "George, M., Hamid, M., and Miller A. Gold Code Generators in Virtex DevicesPDF (126 KB)
  45. ^ "GPS - explained (Signals)"
  46. ^ a b ""How a GPS Receiver Gets a Lock"". Gpsinformation.net. http://gpsinformation.net/main/gpslock.htm. Retrieved 2009-10-13. 
  47. ^ "AN02 Network Assistance". http://www.navsync.com/notes2.html. Retrieved 2007-09-10. 
  48. ^ a b c d e Press, Flannery, Tekolsky, and Vetterling 1986, Numerical Recipes, The Art of Scientific Computing (Cambridge University Press).
  49. ^ Noe, P.S.; Myers, K.A. (March 1976). "A Position Fixing Algorithm for the Low-Cost GPS Receiver". IEEE Transactions on Aerospace and Electronic Systems AES-12 (2): 295–297. doi:10.1109/TAES.1976.308310. http://ieeexplore.ieee.org/xpls/abs_all.jsp?arnumber=4101635. 
  50. ^ a b c Richard Langley (July/August 1991). "The Mathematics of GPS" (PDF). GPS World. http://gauss.gge.unb.ca/gpsworld/EarlyInnovationColumns/Innov.1991.07-08.pdf. 
  51. ^ a b Lundberg, J.B. (2001). "Alternative algorithms for the GPS static positioning solution". Applied Mathematics and Computation (Elsevier) 119 (1): 21--34. doi:10.1016/S0096-3003(99)00219-2. 
  52. ^ a b Bancroft, S. (1985). "An Algebraic Solution of the GPS Equations". Aerospace and Electronic Systems, IEEE Transactions on aes-21: 56–59. doi:10.1109/TAES.1985.310538. http://ieeexplore.ieee.org/xpl/freeabs_all.jsp?arnumber=4104017. 
  53. ^ Jay Farrell, Matthew Barth (1999). The global positioning system and inertial navigation. McGraw-Hill. p. 145. ISBN 007022045X. 
  54. ^ Krause, L.O. (March 1987). "A Direct Solution to GPS-Type Navigation Equations". Aerospace and Electronic Systems, IEEE Transactions on AES-23 (2): 225–232. doi:10.1109/TAES.1987.313376. 
  55. ^ a b Yang Yong and Miao Lingjuan (2004-07-06). "GDOP results in all-in-view positioning and in four optimum satellites positioning with GPS PRN codes ranging". Position Location and Navigation Symposium, 2004. PLANS 2004. pp. 723–727. http://ieeexplore.ieee.org/xpls/abs_all.jsp?arnumber=1309065. 
  56. ^ Peter H. Dana. "Geometric Dilution of Precision (GDOP) and Visibility". University of Colorado at Boulder. http://www.colorado.edu/geography/gcraft/notes/gps/gps.html#Gdop. Retrieved 2008-07-07. 
  57. ^ Peter H. Dana. "Receiver Position, Velocity, and Time". University of Colorado at Boulder. http://www.colorado.edu/geography/gcraft/notes/gps/gps.html#PosVelTime. Retrieved 2008-07-07. 
  58. ^ The same principle, and the math behind it, can be found in descriptions of pulsar timing by astronomers.
  59. ^ SNT080408. "Ephemeris Server Example". Tdc.co.uk. http://www.tdc.co.uk/index.php?key=ephemeris. Retrieved 2009-10-13. 
  60. ^ "Unit 1 - Introduction to GPS". http://seismo.berkeley.edu/~battag/GAMITwrkshp/lecturenotes/unit1/unit1.html#3. 
  61. ^ Česky. "Global Positioning System - Wikipedia, the free encyclopedia". En.wikipedia.org. http://en.wikipedia.org/wiki/Global_Positioning_System#multi_nr. Retrieved 2009-10-13. 
  62. ^ Grewal, Mohinder S.; Weill, Lawrence Randolph; Andrews, Angus P. (2001), Global positioning systems, inertial navigation, and integration, John Wiley and Sons, p. 103, ISBN 047135032X, 9780471350323, http://books.google.be/books?id=ZM7muB8Y35wC , Chapter 5, p. 103
  63. ^ a b "Statement by the President regarding the United States' Decision to Stop Degrading Global Positioning System Accuracy". Office of Science and Technology Policy. May 1, 2000. http://www.ngs.noaa.gov/FGCS/info/sans_SA/docs/statement.html. Retrieved 2009-02-02. 
  64. ^ "GNSS - Frequently Asked Questions - GPS: Will SA ever be turned back on?". FAA. June 13, 2007. http://www.faa.gov/about/office_org/headquarters_offices/ato/service_units/techops/navservices/gnss/faq/gps/index.cfm#ad3. Retrieved 2007-12-17. 
  65. ^ "DoD Permanently Discontinues Procurement Of Global Positioning System Selective Availability". DefenseLink. September 18, 2007. http://www.defenselink.mil/releases/release.aspx?releaseid=11335. Retrieved 2008-02-20. 
  66. ^ "Selective Availability". National space-based Positioning, Navigation, and Timing Executive Committee. http://pnt.gov/public/sa/. Retrieved 2008-02-20. 
  67. ^ Stephen Webb (2004). Out of this world: colliding universes, branes, strings, and other wild ideas of modern physics. Springer. p. 32. ISBN 0387029303. http://books.google.com/books?id=LzQcsSCdeLgC&pg=PA32. 
  68. ^ Rizos, Chris. University of New South Wales. GPS Satellite Signals. 1999.
  69. ^ The Global Positioning System by Robert A. Nelson Via Satellite, November 1999
  70. ^ Pogge, Richard W.; “Real-World Relativity: The GPS Navigation System”. Retrieved 25 January 2008.
  71. ^ "Astronautica Acta II, 25 (1956).". 1956-08-10. http://bourabai.kz/winter/satelliten.htm. Retrieved 2009-10-23. 
  72. ^ Ashby, Neil Relativity and GPS. Physics Today, May 2002.
  73. ^ Cerruti, A., P. M. Kintner, D. E. Gary, A. J. Mannucci, R. F. Meyer, P. H. Doherty, and A. J. Coster (2008), Effect of intense December 2006 solar radio bursts on GPS receivers, Space Weather, doi:10.1029/2007SW000375, October 19, 2008
  74. ^ Aarons, Jules and Basu, Santimay, Ionospheric amplitude and phase fluctuations at the GPS frequencies, Proceedings of ION GPS, v 2, 1994, p 1569-1578
  75. ^ Ledvina, B. M., J. J. Makela, and P. M. Kintner (2002), First observations of intense GPS L1 amplitude scintillations at midlatitude, Geophys. Res. Lett., 29(14), 1659, doi:10.1029/2002GL014770
  76. ^ Tom Diehl, Solar Flares Hit the Earth- WAAS Bends but Does Not Break, SatNav News, volume 23, June 2004
  77. ^ "I-PASS Mounting for Vehicles with Special Windshield Features". http://www.illinoistollway.com/pls/portal/docs/PAGE/TW_CONTENT_REPOSITORY/TW_CR_IPASS/LPT-SPECIALWINDSHIELDLIST.PDF. 
  78. ^ "3M Automotive Films". http://solutions.3m.com/wps/portal/3M/en_US/WF/3MWindowFilms/Products/ProductCatalog/?PC_7_RJH9U5230GE3E02LECFTDQG0V7_nid=9928QS9MGHbeT4DCJBL6BVgl. . Note that the 'Color Stable' films are specifically described as not interfering with satellite signals.
  79. ^ The Hunt for RFI. GPS World. 1 January 2003.
  80. ^ "EMC compliance club "banana skins" column 222". Compliance-club.com. http://www.compliance-club.com/archive/bananaskins/201-225.asp. Retrieved 2009-10-13. 
  81. ^ Low Cost and Portable GPS Jammer. Phrack issue 0x3c (60), article 13. Published December 28, 2002.
  82. ^ American Forces Press Service. Centcom charts progress. March 25, 2003.
  83. ^ "MoD's tests will send satnav haywire so take a road atlas". The Daily Mail. 2007-06-06. http://www.dailymail.co.uk/news/article-460279/MoDs-tests-send-satnav-haywire-road-atlas.html. 
  84. ^ Ruley, John. AVweb. GPS jamming. February 12, 2003.
  85. ^ Commercial GPS Receivers: Facts for the Warfighter. Hosted at the Joint Chiefs website, linked by the USAF's GPS Wing DAGR program website. Retrieved 10 April 2007.
  86. ^ Commanders Digital Assistant explanation and photo
  87. ^ "Latest version Commanders Digital Assistant" (PDF). http://peosoldier.army.mil/factsheets/SWAR_LW_CDA.pdf. Retrieved 2009-10-13. 
  88. ^ Soldier Digital Assistant explanation and photo
  89. ^ Sinha, Vandana (2003-07-24). "Commanders and Soldiers' GPS-receivers". Gcn.com. http://www.gcn.com/print/22_20/22893-1.html. Retrieved 2009-10-13. 
  90. ^ "XM982 Excalibur Precision Guided Extended Range Artillery Projectile". GlobalSecurity.org. 2007-05-29. http://www.globalsecurity.org/military/systems/munitions/m982-155.htm. Retrieved 2007-09-26.