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. ®
COMMENTS
Cost effective
It isn't cost effective to run fiber in rural areas. I live in the "suburb" of a rural town and my street has ~10 houses per mile. Head another mile down the road and the population density drops.
As a result, calling this "indiffferent" is just nuts when compared to areas that are currently served by dial up or satellite. I had satellite internet and while I got DSL-like bandwidth on large file downloads, the latency (1-3 seconds) rendered it barely faster than dial-up for general usage. I finally got DSL when lightning toasted the area's switch and the replacement had just enough signal to get me 768Kb.
Depending on collision avoidance, channel splitting, and the over-subscription factor, each tower could offer DSL-like performance to a couple hundred subscribers. Assuming each subscriber is a family/business, that serves a few thousand people. The tower is likely half the up front cost and less than 10% the long-term maintenance cost of fiber.
Simply not good enough.
There simply isn't enough reliable bandwidth in the sub GHz spectrum to do anything more than fill in a few rural cold spots with what will be by all accounts a highly indifferent service.
The time would be far better spent on sorting out the legalities and costs of laying fibre.
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