08.21.2008 01:30 PM
Performance of unlicensed devices at NFL game debatable

On Aug. 9, prior to and during a preseason NFL game at FedEx Field, in Washington, D.C., spectrum-sensing prototypes from Philips and Singapore’s Institute of Infocomm Research (I2R) were tested, and according to one anti-white space proponent, failed to adequately vacate a busy frequency. Some fear this shows that unlicensed devices will adversely affect wireless microphones and camera performance due to signal interference.

Offering a contrary view, as has been the case in this drawn-out debate, Philips claimed its device performed as designed during the game between the Washington Redskins and the Buffalo Bills and did not interfere with wireless signals.

The tests were conducted by representatives of the FCC to judge the impact on wireless microphones and the ability of these unlicensed devices to detect frequencies being used by broadcast TV signals. The FCC has proposed opening unused parts of the analog broadcast TV spectrum — white spaces — to transmit high-speed data to portable devices. The proposal is supported by consumer electronics companies like Microsoft and Google, which want to use the spectrum for a new generation of wireless routers, network hubs and other file-sharing devices.

Broadcasters and professional audio equipment vendors, like Shure, have been vocally opposed to any new devices operating on spectrum now used for remote sports productions and live Broadway shows.

Mark Brunner, senior director of public and industry relations at Shure, said that in order for the devices to avoid causing interference, they have to detect when signals from either DTV broadcasts or wireless microphones are using part of the spectrum and then move to another unoccupied frequency.

During the tests, the Philips device tended to indicate all the TV channels were occupied, according to Brunner. The I2R device showed unoccupied channels but was consistently unable to detect when microphones were turned on.

Conversely, Philips claimed its prototype devices performed as is required by the FCC. “Our interpretation of the results is that they were very, very favorable for our device," Monisha Ghosh, from Philips Research, told PC Magazine.

"In no test did we ever declare a channel vacant when there was a wireless microphone on it," Ghosh said. "There was never an issue of the white space device creating interference."



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