A white paper released last week looks at the challenges the FCC faces in regulating the growing number of unlicensed devices. The FCC is considering allocating additional spectrum for unlicensed devices, including spectrum now used for TV broadcasting. The paper, Unlicensed and Unshackled: A Joint OSP-OET White paper on Unlicensed Devices and Their Regulatory Issues
, describes the wide range of unlicensed devices currently in use and outlines the need for new policies to address problems of interference.
Some of the Part 15 "intentional radiators" described include spread spectrum and digitally modulated devices, Personal Communications Service devices (wireless PBX systems), National Information Infrastructure devices (wireless LANs and bridges), Ultra-Wideband devices (ground penetrating radar), and general low power devices (baby monitors, door openers, toy wireless microphones).
The spectrum the FCC is looking at for unlicensed devices includes frequencies in the 70, 80 and 90 GHz bands, 3650-3700 MHz and frequencies currently used for TV broadcasting. In the 3650-3700 MHz band, the FCC suggested allowing unlicensed operation with minimal technical requirements at power levels (above 1 W) higher than those allowed in other Part 15 spectrum. Unlicensed operation on TV broadcast frequencies would use channels unsuitable for high power broadcasting due to interference with stations in nearby markets. The white paper used an example of TV Channels 3 and 4. Channel 3 cannot be used for broadcasting in New York due to a co-channel station in Philadelphia and Channel 4 cannot be used for broadcasting in Philadelphia due to Channel 4 being used in New York. However, low power unlicensed devices may be able to use Channel 4 in Philadelphia and Channel 3 in New York. Unlicensed medical telemetry devices are currently allowed to use some TV channels, as any broadcaster initiating DTV broadcasting on a new channel knows.
Interference between unlicensed devices and unlicensed and licensed services remains a concern. For interference between unlicensed devices, the FCC White paper compared this to highways. The road system is open to all drivers, but during rush hour in an urban area they may have to wait in line to access it and experience delays traveling on it. Similarly, users of unlicensed spectrum may anticipate delays and congestion at certain times in urban areas. The ultimate solution, the paper says, "will require a novel technical resolution, a pricing system or some other means to meter competing uses of the network." The automobile analogy would be "smaller cars, carpooling or toll roads."
Receiver performance in the presence of interference will have a major impact on the spectrum available for shared use by unlicensed devices. The FCC Spectrum Policy Task Force has suggested development of an "interference temperature" metric that would set a threshold for the noise environment in which receivers would have to operate. Unlicensed services sharing spectrum with licensed services would require intelligent radios capable of identifying available spectrum and adjusting power levels to avoid interference before transmitting. There is concern, however, that this will make the unlicensed radios too expensive. While smart radios are looking for available spectrum or operating at a very low power level, they may lose contact with the smart receiver with which they are communicating. While complicated, the "interference temperature" approach would allow unlicensed devices to underlay existing licensed services without requiring new spectrum.
When sharing is not practical, new spectrum for unlicensed devices will be needed. Some frequencies currently reserved for government use are being reassigned for unlicensed use (see last week's issue for details on new spectrum in the 5.8 GHz band). Another option would be to clear existing users from spectrum to make it available for unlicensed use.
Interference and available spectrum are only two of the topics covered in the white paper. It contains detailed reports on the wide range of unlicensed devices currently in use, growth in the use of unlicensed devices and predictions for the future of unlicensed services. If you have any interest in Part 15 devices, whether from the standpoint of a user or someone concerned about interference, the OET, Unlicensed and Unshackled: A Joint OSP-OET White paper on Unlicensed Devices and Their Regulatory Issues
is worth reading.