White spaces (radio): Wikis

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In telecommunications, white spaces refer to frequencies allocated to a broadcasting service but not used locally. In the United States, it has gained prominence after the FCC ruled that unlicensed devices that can guarantee that they will not interfere with assigned broadcasts can use the empty white spaces in frequency spectrum.

Contents

Summary

National and international bodies assign different frequencies for specific uses, and in most cases license the rights to broadcast over these frequencies. This frequency allocation process creates a bandplan, which for technical reasons assigns white space between used radio bands or channels to avoid interference. In this case, while the frequencies are unused, they have been specifically assigned for a purpose, such as a guard band. Most commonly however, these white spaces exist naturally between used channels, since assigning nearby transmissions to immediately-adjacent channels will cause destructive interference to both. In addition to white space assigned for technical reasons, there is also unused radio spectrum which has either never been used, or is becoming free as a result of technical changes. In particular, the switchover to digital television frees up large areas between about 50 MHz and 700 MHz. This is because digital transmissions can be packed into adjacent channels, while analog ones cannot. This means that the band can be "compressed" into fewer channels, while still allowing for more transmissions.

In the United States, the abandoned television frequencies are primarily in the upper UHF "700-megahertz" band, covering TV channels 52 to 69 (698 to 806 MHz). U.S. television and its white spaces will continue to exist in UHF frequencies, as well as VHF frequencies for which mobile users and white-space devices require larger antennas. In the rest of the world, the abandoned television channels are VHF, and the resulting large VHF white spaces are being reallocated for the worldwide (except the U.S.) digital radio standard DAB and DAB+, and DMB.

White-space devices

Various proposals, including IEEE 802.22[1][2] and those from the White Spaces Coalition, have advocated using white spaces left by the termination of analog TV to provide wireless broadband Internet access. However, these efforts may impact wireless microphones, medical telemetry, and other technologies that have historically relied on these open frequencies.

A device intended to use these available channels is a white-space device (WSD). These are designed to detect the presence of existing signals, such as TV stations and other wireless users, and to then avoid the use of these channels.[3] Early ideas proposed including GPS receivers and programming each WSD with a database of all TV stations in an area, however this would not have avoided other non-stationary or unlicensed users in the area, or any stations licensed or altered after the device was made.

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United States

Full power analog television broadcasts, which operated between the 54 MHz and 806 MHz television frequencies (Channels 2-69), ceased operating on June 12, 2009 per a United States digital switchover mandate. At that time, full power TV stations were required to switch to digital transmission and operate only between 54-698 MHz. This is also the timetable that the white space coalition has set to begin offering wireless broadband services to consumers. The delay allows time for the United States Federal Communications Commission (FCC) to test the technology and make sure that it does not interfere with existing television broadcasts. Similar technologies could be used worldwide as much of the core technology is already in place.[4]

Theatrical producers and sports franchises hoped to derail or delay the decision, arguing that their own transmissions — whether from television signals or from wireless microphones used in live music performances — could face interference from new devices that use the white spaces. However, the FCC rejected their arguments, saying enough testing has been done, and through new regulations, possible interference will be minimized.

More of the broadcast spectrum was needed for wireless broadband Internet access, and in March 2009, Massachusetts Senator John Kerry introduced a bill requiring a study of efficient use of the spectrum.[5]

White Spaces Coalition

The White Spaces Coalition consists of eight large technology companies that plan to deliver high speed broadband internet access beginning in February 2009 to United States consumers via existing "white space" in unused television frequencies between 54-698 MHz (TV Channels 2-51). The coalition expects speeds of 80 Mbps and above, and 400 to 800 Mbps for white space short-range networking.[6] The group includes Microsoft, Google, Dell, HP, Intel, Philips, Earthlink, and Samsung Electro-Mechanics.

The White Spaces Coalition formed in late 2006, soon after the Senate set the date to cease analog broadcasts. It doesn't appear to have a website, but many of the companies involved in the White Spaces Coalition are also involved in the Wireless Innovation Alliance.

Google sponsored a campaign named Free the Airwaves with the purpose of switching over the white spaces that will be cleared up in 2009 by the DTV conversion process by the FCC and converted to an un-licensed spectrum that can be used by Wi-Fi devices.[7] The National Association of Broadcasters disapproves of the project because they claim that it would reduce the broadcast quality of their TV signals.[8]

Preliminary test

The Federal Communications Commission's Office of Engineering and Technology released a report dated July 31, 2007 with results from its investigation of two preliminary devices submitted. The report concluded that the devices did not reliably sense the presence of television transmissions or other incumbent users, hence are not acceptable for use in their current state and no further testing was deemed necessary.[9]

However, on August 13, 2007 Microsoft filed a document with the FCC in which it described a meeting that its engineers had with FCC engineers from the Office of Engineering and Technology on August 9 and 10. At this meeting the Microsoft engineers showed results from their testing done with identical prototype devices and using identical testing methods that "detected DTV signals at a threshold of -114 dBm in laboratory bench testing with 100 percent accuracy, performing exactly as expected." In the presence of FCC engineers, the Microsoft engineers took apart the device that the FCC had tested to find the cause of the poor performance. They found that "the scanner in the device had been damaged and operated at a severely degraded level" which explained the FCC unit's inability to detect when channels were occupied. It was also pointed out that the FCC was in possession of an identical backup prototype that was in perfect operating condition that they had not tested.[10]

FCC decision

TV broadcasters and other incumbent users of this spectrum (both licensed and unlicensed, including makers of wireless audio systems) feared that their systems would no longer function properly if unlicensed devices were to operate in the same spectrum. However, the Federal Communications Commission's Office of Engineering and Technology released a report dated October 15, 2008, which evaluated prototype TV-band white space devices submitted by Adaptrum, The Institute for Infocomm Research, Motorola and Philips. The report concluded that these devices had met the burden of "proof of concept" in their ability to detect and avoid legacy transmissions,[11] although none of the tested devices adequately detected wireless microphone signals in the presence of a digital TV transmitter on an adjacent channel.

On November 4, 2008, the FCC voted 5-0 to approve the unlicensed use of white space,[12] thereby silencing opposition from broadcasters. The actual Second Report and Order was released ten days later and contains some serious obstacles for the development and use of TV Band Devices as they are called by FCC. Devices must both consult an FCC-mandated database to determine which channels are available for use at a given location, and must also monitor the spectrum locally once every minute to confirm that no legacy wireless microphones, video assist devices or other emitters are present. If a single transmission is detected, the device may not transmit anywhere within the entire 6 MHz channel in which the transmission was received.[13] It is hoped that, within a year, this new access will lead to more reliable WiFi and other technologies.

Broadcaster lawsuit

On February 27, 2009, the National Association of Broadcasters (NAB) and the Association for Maximum Service Television, Inc. (MSTV) asked a Federal court to shut down the FCC's authorization of white space wireless devices. The plaintiffs allege that portable, unlicensed personal devices operating in the same band as TV broadcasts have been "proven" to cause interference despite FCC tests to the contrary. The lawsuit was filed in a United States Court of Appeals for the District of Columbia Circuit. The Petition for Review states that the FCC's decision to allow white space personal devices "will have a direct adverse impact" on MSTV's and NAB's members, and that the Commission's decision is "arbitrary, capricious, and otherwise not in accordance with law."[14]

See also

References

  1. ^ "IEEE 802 LAN/MAN Standards Committee 802.22 WG on WRANs (Wireless Regional Area Networks)". IEEE. http://www.ieee802.org/22/. Retrieved 2009-01-18.  
  2. ^ Carl, Stevenson; G. Chouinard, Zhongding Lei, Wendong Hu, S. Shellhammer & W. Caldwell (2009-01). IEEE 802.22: The First Cognitive Radio Wireless Regional Area Networks (WRANs) Standard = IEEE Communications Magazine. 47. US: IEEE. pp. 130–138. http://dx.doi.org/10.1109/MCOM.2009.4752688.  
  3. ^ "'White Spaces' Issue Remains Murky," Broadcasting & Cable, August 18, 2008.
  4. ^ Eric Bangeman. The White Spaces Coalition's plans for fast wireless broadband: Fast broadband without fiber... or even wires", Ars Technica, 2007-4-17. Retrieved on June 12, 2007.
  5. ^ Eggerton, John (2009-10-05). "Broadcasters Tackle Spectrum-Sharing Debate". Broadcasting & Cable. http://www.broadcastingcable.com/article/356595-Broadcasters_Tackle_Spectrum_Sharing_Debate.php?rssid=20065&q=digital+tv. Retrieved 2009-10-09.  
  6. ^ Eric Bangeman. The White Spaces Coalition's plans for fast wireless broadband: The technology", Ars Technica, 2007-4-17. Retrieved on June 12, 2007.
  7. ^ http://www.freetheairwaves.com/
  8. ^ http://news.cnet.com/8301-1035_3-10019517-94.html
  9. ^ Initial Evaluation of the Performance of Prototype TV Band White Space Devices [1], 2007-7-31. Retrieved on August 2, 2007.
  10. ^ Microsoft: FCC tested broken white spaces device, neglected backup unit [2], 2007-8-15. Retrieved on August 15, 2007.
  11. ^ Evaluation of the Performance of Prototype TV Band White Space Devices, Phase II [3], 2008-10-15. Retrieved on October 24, 2008.
  12. ^ Harold Feld And now the moment we've all been waiting for WHITE SPACES", WetMachine.com, 2008-11-4. Retrieved on November 5, 2008
  13. ^ Second Report and Order
  14. ^ Petition for Review

External links


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