Rural white space wireless standard signed off
After seven years, 802.22 is official
Nearly seven years after the IEEE’s 802.22 working group was first formed, the 802.22 standard has been published.
The standard is designed to take advantage of television “white space” frequencies between channels. As countries roll out digital television and reallocate the spectrum previously occupied by broadcasters, vacant channels become more common. In America, carriers are fighting a rearguard action against the FCC’s white space spectrum rules; trials are underway in the UK; while the use of old analogue TV spectrum is the matter of intense lobbying by carriers, broadcasters and emergency services in Australia.
The 802.22 standard – already being wrongly-identified as a Wi-Fi standard by world+dog – has to support a huge range of carrier frequencies to live in the television spectrum: from 54 MHz up to 862 MHz.
It has to cope with other challenges as well: the physical and MAC layers have to be able to cope with long round trips between towers and end users, and to support propagation at up to 33 Km from the base station, the standard also needs to cope with channel fading.
The other big challenge is deciding which channels to use, since the frequency that happens to be lying fallow in any given location will depend on which TV channels are in use. The “cognitive radio” systems defined under 802.22 have a range of protections designed to prevent interference with local TV broadcasts: base stations can sense the presence of broadcasts, and also combine GPS geolocation with a spectrum database lookup to identify channels that should be vacant in a given location.
An addendum to the standard to protect wireless microphone users, 802.22.1, is nearly complete and should follow shortly.
The standard is designed to deliver “up to 22 Mbps” in an 8 MHz TV channel (its best-case spectral efficiency when all is well is 3.12 bits/Hz), but that capacity is designed to be shared between as many as a dozen users per tower.
A presentation by the 802.22 working group can be downloaded here. ®
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