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A Landslide for White Spaces
12/3/2008

WASHINGTON
Bulldozed by the unanimous FCC vote Nov. 4 opening up DTV white spaces to unlicensed devices, broadcasters now are fighting to minimize the interference the future devices will cause once they are unleashed onto the airwaves.

The new rules, outlined last month by Chairman Kevin Martin but not yet released, would allow unlicensed devices on unused DTV channels, including adjacent channels, at power levels close to those proposed by Google and other members of the White Space Coalition, a group of high-tech companies with plans for future white space devices.

In a statement, the commission called the plan "a careful first step" with "numerous safeguards" against interference to incumbent users. Martin bragged in a statement that tests by the FCC Office of Engineering and Technology were "an extraordinary step... to prove the concept that white space devices could be safely deployed"—a conclusion strongly disputed by broadcasters.

FREE EVERYTHING

Martin, widely expected to leave the commission as the presidency changes hands, echoed the promises of Google and other white space advocates, promising "WiFi on steroids."

"Consumers across the country will have access to devices and services that they may have only dreamed about before," Martin said.

Under the plan, devices would be allowed to operate if they use spectrum-sensing technology and geolocation databases to detect and avoid DTV channels and to protect certain sensitive sites like cable headends. Devices would be allowed to use spectrum-sensing technology alone if they can show to the FCC that it actually works in specific devices. So far, the spectrum-sensing abilities of prototype devices have had mixed results, and broadcasters have slammed the technology as unreliable.

"Even the FCC cannot compromise the laws of physics," the Association for Maximum Service Television said in a statement.

MSTV told the commission Oct. 31 that the least the FCC could do is subject the devices to rigorous testing beforehand and ensure fair and reliable tests to prevent interference to DTV. In a filing, MSTV also attacked the FCC proposal that a device should be able to detect signals as low as -114 dBm, a level MSTV equated with setting a smoke detector to only be able to detect a raging fire.

"The commission must... begin anew to evaluate the appropriate sensing threshold for a sensing-only device," MSTV said.

INTERFERENCE LIMITS

Under the rules, portable devices that use both spectrum-sensing technology and geolocation databases will be limited to 100 mW of power, or 40 mW when operating on channels adjacent to active DTV channels. Spectrum-sensing-only devices—if they can prove viability at the OET—would be limited to 50 mW, or 40 mW on adjacent channels. MSTV has said that power level would "eviscerate" DTV in some areas.

Fixed devices (say, base stations for rural Internet networks) would operate at a maximum of 4 W, and not at all on adjacent channels unless they can show to the OET that they can avoid interfering with DTV. MSTV wants no fixed devices on the adjacent channels and portable devices at just 5 mW on those channels and 10 mW on the other channels.

The Martin plan not only largely complies with what Google demanded, but even met the timeline dictated by Google founder Larry Page, who said he wanted the FCC to make the rules by Election Day—although Martin, in his trademark style, started the actual meeting on the subject several hours late.

TESTING, TESTING

To protect the thousands of incumbent wireless mic users, the new white space regime will rely on spectrum-sensing technology along with a geolocation database for large events.

But spectrum-sensing, to wireless mic maker Shure Inc., is a non-starter.

"Test data from microphone tests is less favorable to sensing than the DTV data, but gets buried at the back of the report," Shure told the FCC in its filing in support of a fresh comment period on the data. "It is also heavily redacted. Individual tests are not published."

Shure says the OET failed to make a case that the future white space devices would not interfere with wireless mic use.

"While not unexpected, today's FCC decision will greatly complicate the lives of wireless microphone users across the United States and negatively affect tens of millions of Americans listening to live and broadcast events," Mark Brunner, Shure senior director for global public and industry relations, said in a statement.

Shure had offered its own plan for protecting wireless mics. It would designate "minimally sufficient protected channels" centered around Channel 37 and Channel 11, with all new white space devices managed by a geolocation database that would reflect events, such as sports, that involve abundant mic use. The Shure plan also called for six protected UHF channels (reduced to four channels after three years) and two protected VHF channels, for smaller operations.

But relying in many cases on spectrum-sensing alone—as envisioned by the FCC order—will remain problematic.

"The stuff doesn't work, for any host of technical reasons," said Ahren Hartman, director of platform engineering for Shure. "The failure rates were just abysmally high. It's unbelievable that they can come to that conclusion [that spectrum-sensing will be adequate] when they stood there and watched the tests."

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