Motorola has updated the white space device it has submitted to the FCC, adding features to improve its sensing of adjacent channels.
As the FCC Office of Engineering and Technology moved from the lab into field testing of white space devices and their ability to detect (and thus avoid interfering with) DTV signals, Motorola also encouraged the commission to test its device in its “preferred” mode of operation, relying primarily on a geolocation database to protect incumbents.
To improve adjacent channel testing, Motorola added a switchable attenuator to the front end of the device to flatten out channels adjacent to the one to which the receiver is tuned, said Steve Sharkey, Motorola director of spectrum and standards strategy. That prevents the receiver from getting swamped by the adjacent channels and tackles one of the concerns broadcasters have voiced about spectrum-sensing technology and its limitations.
But Friday, the Association for Maximum Service Television said it observed labs tests of the new device, and said it failed in some cases.
“In the presence of a moderate or strong adjacent channel, they were not able to sense the presence of a DTV signal,” MSTV President David Donovan said.
Sharkey disputed that.
“The characterization by MSTV is absolutely false,” he said. “They are misrepresenting the tests.”
Sharkey said the devices were able to detect any DTV signals a DTV receiver in the same situation would be able to detect—with plenty of margin for good measure.
“We believe the tests were fully successful, testing down to a level that will fully protect viewers,” he said.
Motorola also plugged the notion of a geolocation database to protect incumbent users. Under the Motorola plan, white space devices would receive updates (likely over an Internet connection) of incumbent users (such as wireless users coming into town for a football game, for example.)
Motorola’s multi-tiered incumbent protection scheme also includes beacons used by incumbent devices with unplanned moves (such as ENG equipment)
Broadcasters have been fighting hard against allowing unlicensed mobile devices to operate in white spaces, or unused DTV channels, and some microphone makers and users have also asserted that disaster could befall them if unlicensed devices are set loose in the frequencies.
“The costs of building a beacon would be very low, and it is a straightforward technology,” said Sharkey. “It wouldn’t be a significant impediment.”
Mic maker Shure Inc. urged the FCC to test such beacons themselves, saying such devices are “still on the drawing board.”
“This [beacon] proposal is particularly troubling because it wrongly requires incumbent users to shoulder the burden for interference protection from new devices,” Shure said in a 25-page filing May 6 that explores the beacon issue and other protection proposals.
“Motorola’s plan incorporates a set of cumbersome operational requirements that wastes spectrum and that make it wholly unfit for use by a significant portion of wireless microphone users, including, for example, news teams covering breaking news or sporting events.” Shure said. “Put simply, the case has not been made to move forward with any of the portable white space proposals at this time. Instead, the commission should refocus its attention to examining fixed service proposals that protect wireless microphones and DTV from interference by keeping channels adjacent to DTV stations clear of new white space device transmissions.”
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