08.15.2008 12:00 AM
Philips Disputes White Space Test ‘Failures’
Wireless mic maker Shure Inc. said prototype devices aimed at detecting occupied TV channels fumbled at an NFL Game and bombed on Broadway.
But Philips, one of two entities with a device in the final week of tests by the FCC Office of Engineering and Technology, views the trials differently, noting that its box successfully detected channels as occupied—whether by DTV, NTSC or wireless mic signals.
Shure said in a press release that the prototype devices (actually technology demonstration devices as opposed to prototypes of future products) “were unable to consistently identify operating wireless microphones or distinguish occupied from unoccupied TV channels.” Philips disputes that interpretation
The tests—Aug. 9 at FedEx field outside Washington, D.C., and Aug. 12 at the Majestic Theater in New York—were the last on the OET’s schedule. Philips, along with companies including Motorola, Microsoft, Google, Intel and others, hopes the tests will show that devices can operate on the unused channels of the DTV spectrum without interfering either with television or the wireless mics that also use the channels.
Shure Senior Director for Public and Industry Relations Mark Brunner said the Philips device consistently showed channels to be nearly completely occupied even before wireless mics were turned on, while the other (from the Institute for Infocomm Research , backed by the government of Singapore) had the opposite problem, failing to detect occupied channels even after the mics were turned on.
Monisha Ghosh of Philips Research said the Philips device detected channels as occupied because they were in fact occupied—by television signals that in some cases were too weak for a regular handheld spectrum analyzer to detect. The Philips device detects whether a channel is occupied but does not display the strength of the detected signals or distinguish whether they come from wireless mics or television transmitters. It detects TV signals at a level far weaker (less than -120 dBm) than what is viewable on television or can be picked up by conventional spectrum analyzers, she said.
In the case of the FedEx Field tests, she said that in one round of testing—on the football field itself—the device successfully detected a mic turning on (on Channel 31). At higher locations, it detected that channel as occupied from the start, consistent with what FCC data indicated it might detect, she said. Once the device detects a channel as occupied by any source, that channel would be avoided by a future white space device, so there’s no need to further detect low-power wireless activity on the same channel.
“If a wireless mic is using a channel that already has a DTV or NTSC channel on it, the white space device is actually providing more protection [than a wireless mic],” she said.
She said at the NFL test, wireless mics operated on 11 channels at 250 mW. In New York, they operated on six channels at 50 mW. Wireless mics use TV channels but generally don’t cause interference because they are low-power and because they function poorly on channels already occupied by strong TV signals, sending operators onto channels with weaker or apparently nonexistent signals.
An “empty” channel is a relative term in any event, as what’s empty for one use might mean interference in another, and almost no channels can be considered absolutely free of all activity.
At both test sites, OET staff turned off all mics to clear the air as much as possible, scanned the channels, and then turned mics on to see what could be detected. They repeated the drill at about three locations within each site—all before the football game and the musical actually began.
Shure, broadcasters, and others urging a cautious approach on white space had prodded the FCC to conduct the NFL and Broadway field tests.
A Singapore-based representative of the Institute for Infocomm Research who has been present at FCC tests did not respond to an e-mail seeking his comment on the tests.
The FCC has no further tests scheduled, and has not stated exactly when it will release test results, although Chairman Kevin Martin said answers by the end of summer were unlikely.