White space tests get mixed results

Field tests to determine whether the Federal Communications Commission should open up unused TV spectrum for wireless broadband services are getting mixed reviews as different methods for avoiding spectrum interference are being tested in the real world.

In the most recently concluded tests, Motorola claims its geolocation-based technology got high marks for avoiding interference with existing spectrum holders, while a field test of spectrum sensing technology at a major sporting venue proved that that technology is not up to snuff in avoiding interference with broadcast-based microphones.

The FCC has been conducting these real world tests of different prototype devices to see if companies can develop products that use buffer spectrum between licensed broadcast channels. This spectrum known has "white space" sits between broadcast TV channels in the 150 MHz to 700 MHs spectrum bands.

Several technology companies, including Motorola, Microsoft, and Google have been lobbying the FCC for more than a year to open up these channels,which would provide between 300 MHz to 400 MHz of unlicensed spectral capacity throughout the country that could be used by anyone. These tech companies believe this spectrum, which is ideal for sending data wirelessly over long distances and penetrating through walls, can be used to enhance or create new wireless broadband services. And they say they can develop products and services that use this spectrum without interfering with services running on licensed spectrum in adjacent bands.

Some of the 700MHz spectrum was already auctioned off by the FCC earlier this year. And companies such as Verizon Wireless, which won a big chunk of the spectrum, plan to use it to build a next generation wireless broadband network.

But incumbent spectrum license holders such as TV broadcasters and cell phone operators, including Verizon Wireless, say wireless devices that access this unlicensed spectrum will cause interference in the neighboring spectrum bands.

Over the weekend, spectrum sensing prototypes were tested by the FCC at the FedEx field in Maryland prior to Saturday's game between the Washington Redskins and the Buffalo Bills. Shure, a microphone manufacturer said in a press release issued Sunday that the spectrum-sensing white-space devices caused "harmful interference to wireless microphones" during the live event.

"Simply stated, the prototype devices were unable to consistently identify operating wireless microphones or distinguish occupied from unoccupied TV channels," said Mark Brunner, Shure's senior director of public and industry relations. "More troubling, the devices failed to detect the presence of wireless microphones when switched on--an occurrence that takes place multiple times during any NFL game."

Motorola, which uses a totally different method for avoiding interference, agrees that sensing technologies don't always work appropriately. That's why the company uses GPS-based geolocation technology and an FCC data base of known spectrum license holders to pick and choose when white spectrum is available.

"There's no question that the geolocation technology that was tested is reliable," said Steven Sharkey, Motorola's senior director for regulatory and spectrum policy. "But on the sensing side, it didn't always detect usable and unusable channels in different areas. These results reflected what we saw in the lab under certain conditions."

Google said in a policy blog last week before the microphone test at FedEx field that the sensing technology may not work as well as some had hoped. Google emphasized that other technologies exist that can ensure that there is no interference with others. And the company outlined an alternative technical approach in a proposal filed with the FCC in March, which uses geolocation technology along with beacons and/or safe harbors.

"Taken together, these protection mechanisms remain technically unimpeachable, whether or not the Commission's current testing process produces adequate data to validate a spectrum sensing-only approach," Richard Whitt, Google's top policy wonk said in his blog. "Moreover, no WSD (white space device) will--or should--come to market unless the FCC can verify that the device does not interfere with TV or wireless microphone signals."

Shure's spokesman Brunner is not completely sold on geolocation technology as the only answer to the white space debate. While the solution may work well for avoiding known TV broadcasters, it might now solve the problem of microphone users who often have broad spectrum licenses to use the same spectrum that Google, Motorola, and others also want to use. Instead, he said he would like to see the industry continue to work on sensing technologies and combine it with beacon technology to provide even further protection.

The FCC is currently compiling results from its testing, and it's expected to release a full report of the results within the next few weeks after it concludes all field tests of the current technology.