Prototypes of spectrum sensing devices performed poorly at a White Spaces test the Federal Communications Commission conduced on Aug. 9 before and during the preseason NFL game between the Washington Redskins and the Buffalo Bills, according to Mark Brunner, senior director of public and industry relations at pro-audio vendor Shure.
The FCC has been exploring the idea of opening unused parts of the analog broadcast TV spectrum -- dubbed white spaces -- to transmit high-speed data to portable devices.
While the idea is backed by major technology firms, including Microsoft and Google, it has been criticized by broadcast and pro audio companies. They fear the devices might interfere with the transmission of DTV signals and wireless microphones.
The issue is particularly important for high-def content, both in the transmission of HD broadcast signals and the use of wireless microphones in sporting or concert events using wireless microphones, Brunner said.
“HD is the fertile ground where all this stuff comes together,” he said. “People are buying HD sets because they want to have the ultimate viewing experience. If there is a possibility that the creation of this content and then the delivery of this content could be compromised by these devices than that should be a serious cause for concern. It is why the broadcasters and pro audio community has raised cautionary flags.”
The Aug. 9 test was designed to test the potential impact on wireless microphones during a sporting events and the ability of spectrum sensing devices to detect what frequencies were already being used by broadcast TV signals or wireless microphones.
In order for the White Space devices to work without causing interference, the spectrum sensing devices would need to be able to detect when signals from either DTV broadcasts or wireless microphones are using part of the spectrum and then make certain the devices operate on an unoccupied frequency.
The test focused specifically on prototype sensing devices from Philips and Singapore’s Institute of Infocomm Research (I2R), Brunner noted.
During the tests, the Philips device tended to indicate all the TV channels were occupied, according to Brunner. The second I2R device showed unoccupied channels but was consistently unable to detect when microphones were turned on.
“If any conclusion can be drawn from the test, it is that spectrum sensing technology -- at least as it has been demonstrated in prototype form to date -- should not be relied on to protect wireless microphones,” Brunner said. “The field test is further validation that spectrum sensing technology is not in a state that would offer reliable protection to wireless microphones.”