Chairman Martin gives tentative stamp of approval

FCC Chairman Kevin Martin weighed in his support for “white space” wireless devices, allowing unlicensed (e.g. free-for-all) usage of vacant Digital TV channels.

Backers of the white space wireless call it “Wi-Fi on steroids,” noting that TV frequencies, which generally cover the 55 MHz to 800 MHz chunk of wireless spectrum, excel at broadcasting signals over a large distance and penetrating obstructions – a difficult feat for today’s 2.4 GHz networks.

White space wireless faces stiff resistance from TV broadcasters concerned about signal interference. Unlike analog, where low-quality signals produce an acceptable-but-snowy picture and image ghosting, digital signals will cut out entirely at worst, or exhibit heavy distortions at best.

The response, so far, has been to develop “smart” wireless transmitters that limit themselves only to DTV channels available by a given margin, and actively scan the frequency to determine what areas are free. To that end, the FCC recently wrapped up Phase II of its test program for prototypes, and the results went so well that backers received Martin’s endorsement.

An executive summary of the test results (PDF), posted on the FCC website, notes that “fixed location” white-space devices are already set to be allowed into the TV spectrum in February 2009, immediately after analog TV signals cease broadcasting. Instead, the FCC’s testing pertains specifically to portable devices, such as laptop Wi-Fi cards, that roam from area to area. The “smart” features of these devices work in a variety of ways: open channels are could be located through a TV-style auto-scan, and/or through a nationwide database of TV channel assignments.

White space-scanning technology isn’t yet perfected, however, although the FCC certified that it officially reached “proof of concept” status. Prototype devices submitted by five companies – Adaptrum, the Institute for Infocomm Research (I2R), Microsoft Corporation, Motorola Inc., Philips – were able to scan the TV spectrum in anywhere from 0.1 to 130+ seconds per channel, and on average were able to detect a “clean” channel’s availability on signals as weak as -126 dBm. Real world testing didn’t fare as well, however, as devices both required a stronger signal and exhibited a higher rate of false positives and – more importantly – negatives.

A false negative would mean the auto-scan detects an occupied channel as vacant – a scenario that TV broadcasters and wireless microphone manufacturers deeply fear. It’s a scenario they fear so much, in fact, that some have gone so far as to request a two-channel buffer on either side – meaning 5 consecutive, unoccupied channels – for a device to determine a channel as “empty”. The technology’s backers say 5 channels are excessive, and fear it might cripple the tech’s usefulness.

White space’s backers include heavy hitters like Microsoft and Google – who offered to host the channel database – while its opponents include the National Association of Broadcasters and Shure, Inc, makers of wireless microphones used at concerts and sporting events.

The transition to digital TV means a substantial overhaul to the U.S.’ wireless spectrum allocations: with the dust just beginning to settle over the hotly-contested $19.6 billion 700 MHz band, manufacturers of devices for the overly-crowded 800 MHz, 2.4 GHz, and 5.8 GHz wireless bands will receive a much-needed boost to the amount of spectrum available to them.

The FCC is scheduled to vote on whether or not to allow personal white space devices November 4.

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