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11.09.2005 12:00AM
Scientists: Unlicensed Devices Using TV Channels Won't Interfere with TV Reception
A few weeks ago I mentioned the MSTV Video Your Neighbor's Static in RF Report. It showed the interference unlicensed devices operating on unused TV channels could cause to TV reception. A group of respected scientists say this is not the case in an issue brief titled Reclaiming the Vast Wasteland - Why Unlicensed Use of the White Space in the TV Bands Will Not Cause Interference to DTV Viewers. The brief outlines the methods for avoiding interference to TV reception described in the FCC Notice of Proposed Rulemaking in Docket 04-186 and describes how these will protect TV broadcast reception. The authors of the paper are Michael Marcus, a former Associate Chief at the FCC's Office of Engineering and Technology who is now director of Marcus Spectrum Solutions; Paul Kolodzy, a former Chair of the FCC's Spectrum Policy Task Force who is now a communications consultant; and Andrew Lippman, a founding Associate Director of the MIT Media Lab who is now director of the Viral Radio Program, which *explores ways to use mesh architectures to make energy and spectrum-efficient scalable radio communications systems."

It specifically refutes the demonstrations in the MSTV video, Your Neighbor's Static, saying "Informal discussions with an individual involved with the production of the video reveal that the simulated unlicensed device exploited a longstanding loophole in FCC Rules that has never caused a problem using real transmitters in the field. The device demonstrated is reported to be a 54-MHz-wide noise generator (covering the bandwidth of nine TV channels)--essentially an ultrawideband transmitter. This device would normally be forbidden by existing and proposed FCC Rules, but the loophole permits it to be used in existing unlicensed bands in conjunction with a more powerful signal limited to 6 MHz." The loophole refers to the limits on spurious out-of-channel emissions in relation to the primary signal. FCC rules allow a certain level of spurious emissions, but authors of the paper say, " This loophole in the Part 15 unlicensed rules, which would theoretically permit ultrawideband emissions in TV spectrum, can be closed once and for all if the FCC includes in its Report and Order in this proceeding an additional easily-measured total limit on power in the TV bands for out-of-band emissions."

The paper addresses one major concern of broadcasters, arguing, "The statement of broadcast interests that 'once unlicensed devices are permitted in a licensed band, there is no way to remove them' is overly dramatic and does not reflect contemporary technology." As with the ultrawideband emission problem, the solution, the paper says, is to tighten the FCC rules on these unlicensed devices. "The FCC should require that the internal software used by unlicensed devices to share the TV band white space be capable of being updated at a specified interval, so that the FCC will be able to modify the operating criteria of these systems based on experience, and even turn them all off if it so chooses. While this approach may be difficult for some types of transmitters, the transmitters in this proposal are expected to be connected to the Internet on a regular basis, and thus could check for software updates without requiring user intervention."

The paper also recommends the final rules include protection for cable headend and translator input locations and avoid the use of frequencies used by cable head ends and translators in their area. Translators and cable headends would have to register with the FCC to be guaranteed protection.

The issue brief also addresses concerns including interference to wireless microphones and public safety communications. The paper,"Reclaiming the Vast Wasteland: Why Unlicensed Use of the White Space in the TV Bands Will Not Cause interference to DTV Viewers" is well written. While it refutes broadcasters' arguments against unlicensed devices on unused TV channels, for these arguments to be validated the FCC must clarify and strengthen existing rules before unlicensed devices are allowed in the TV band. If the paper's recommendations are included in the FCC rules, it should benefit both broadcasters and unlicensed users of unused TV channels.


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