Philips Tweaks Algorithm, Claims Greater Sensitivity in White Space Prototype
August 31, 2007
Philips Electronics pressed the FCC again this week to recognize that its prototype white space device (WSD) detects DTV and other RF signals well enough for the FCC to make rules allowing future use of mobile devices, such as Web browsers or wireless home networking gear, that operate in unused DTV channels. Philips said in an Aug. 27 filing that the FCC lab’s bench tests of the company’s Prototype B device, which demonstrated it could detect signals as weak as –114 dBm, showed the technology would not interfere with DTV signals. But in case that sensitivity wasn’t enough, Philips personnel met the next day with nine staff members of the FCC Office of Engineering and Technology to announce a fresh revelation: With some modifications to the algorithm of Prototype B, it reliably detected signals as low as –116 dBm. Broadcasters and others aren’t impressed. NAB and the Association for Maximum Service Television (MSTV) told the FCC that it doesn’t matter whether the device can detect signals at –114 dBm or –116 dBm. It will still present too much risk of interference to DTV, the groups said. Shure, a manufacturer of wireless mics, attacked the WSD industry’s interpretation of the FCC tests. “[The] tests prove what Shure, the IEEE 802.22, NAB/MSTV and the DTV manufacturers have already correctly asserted—unlicensed operations within adjacent channels will create harmful interference that cannot be mitigated,” the company told the commission. Sports producers—college and pro—also weighed in again, worried of interference to their complex wireless audio systems. And, the consequences of WSD-related interference go well beyond television reception, GE Healthcare reminded the FCC. “Due to their low-power transmitters and sensitive receivers, medical telemetry systems are vulnerable to (i) co-channel interference... as well as (ii) overload desensitization from strong adjacent channels signals,” the company wrote. “Moreover, most medical telemetry systems employ distributed antenna systems that combine received signals from many antennas distributed throughout the entire coverage area—typically hundreds of thousands of square feet. In such systems, a single interferer can cause loss of monitoring to all patients, regardless of their location within the coverage area.” Microsoft, whose Prototype A device failed the FCC’s signal detection tests, has claimed its device was damaged and has requested a repeat round of testing.
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