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TV white space defies boffins

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More than three years ago, your reporter got a good taste of how miserable technology utopians can be.

It was at Intel's Developer Forum in San Francisco, and the debate was about liberating analog TV spectrum for exciting new digital uses. The analog switchover is slated for February 2009.

On behalf of Microsoft, Google, and Intel, the technology evangelists argued that smart radios were here, but the evil regulator the FCC wouldn't permit them to deploy the technologies. Broadcasters countered that these experimental new technologies caused interference with their signals (see Abolish Free TV - Intel).

In the hallways afterwards, one delegate and deregulation evangelist couldn't understand why the FCC couldn't just confiscate the spectrum from the TV broadcasters and be done with it?

"Why do the broadcasters need any spectrum at all?" she asked.

Because free TV is one of the few pleasures some Americans can afford, perhaps. A slightly less arrogant and more technically adept argument was advanced instead, which claimed that the space between allocated TV channels was "beachfront property". Instead, the regulator copped it - it was all the fault of the FCC's "command and control" outlook.

(The deregulation fanatics want a spectrum free-for-all and dream of the FCC being scrapped. The FCC is permitting fixed WSDs (white space devices) from 2009, but the industry wants mobile handheld WSDs to be permitted too.)

Now, agile radio has been tested and found to be not quite so agile as its proponents touted.

Hiss, crackle

At the end of July, the FCC's engineering office published two sets of results from a four month trial of agile radio equipment submitted by the "White Space Coalition", which includes Microsoft, Google, Intel, Dell, and HP.

"Depending on the effectiveness of shielding of a TV receiver's tuner, emissions within a broadcast white space (i.e., within an unused broadcast channel) could potentially cause co-channel interference to a TV receiver tuned to a digital cable channel that overlaps the spectrum of the white-space device emission," the FCC noted.

The lab found that the spectrum sensing of the equipment it tested couldn't detect the white space with sufficient accuracy.

For one prototype sensor, "the results of the bench test for determining the baseline minimum detection sensitivity demonstrates that the device will not meet the manufacturer-specified threshold of -114 dBm (or the IEEE 802.22 proposed threshold of -116 dBm for fixed devices) and in fact, fails to meet both of the thresholds by about 20 dB. The results of the field tests also demonstrate inconsistent performance", noted the FCC. The manufacturer may have misread the spec, it suggests. The sensor also failed to detect the presence of a wireless microphone at all.

A second prototype sensor performed to the 114 dBM but got confused when a second DTV channel was turned on - the manufacturer asked it be excluded from more real-world tests. This prototype also failed to pick up a wireless mic, except on the two lowest channels. Both were also severely hampered by the microphones themselves.

Tests of a prototype transmitter also demonstrated interference, and generated some skepticism from engineers whether the filtering required to avoid knocking out TV signals can be implemented in a real product.

So smart radios have a long way to go, and this white space looks less like a "beachfront property" and more like a Cambodian minefield.

Microsoft told the Washington Post today that it had given the FCC a successful demonstration last week - and insisted it will all work out in the end.

As soon as it's got the pesky physics sorted out. ®

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