The FCC released the Third Memorandum Opinion and Order (FCC 12-36) regarding use of unlicensed "white space" devices in the TV broadcast bands. The Memorandum Opinion and Order (MO&O) increases the maximum height above average terrain (HAAT) for sites where fixed devices may operate, modifies adjacent channel emission limits to specify a fixed rather than relative out-of-band emission limit and slightly increases the maximum permissible power spectral density (PSD) for each category of TV bands device.
The MO&O states, "These changes will result in decreased operating costs for fixed TVBDs [TV Band Devices] and allow them to provide greater coverage, thus increasing the availability of wireless broadband services in rural and underserved areas without increasing the risk of interference to incumbent services."
The new rules increase the maximum HAAT for a fixed device antenna to 250 meters, but kept the maximum allowed height above ground at 30 meters. The National Association of Broadcasters did not object to the HAAT increase. The FCC said that it could revisit the height limit in the future "if experience with TV bands devices indicates they could operate at higher antenna heights without causing interference." To reduce the chance of interference, the FCC made changes in the required separation distances from a digital or analog TV (full service or low power) protected contour. Devices operating with an HAAT of 200 to 250 meters must be 31.2 km from the protected contour of a co-channel station and 2.4 km from an adjacent channel station.
The FCC changed the out-of-band emission rule that required emissions in an adjacent channel to be at least 55 dB below the highest emission in the operating channel to a rule with a fixed adjacent channel limit. The limit varies depending on the type of device, ranging from a limit of -42.8 dBm in a 100 kHz bandwidth for fixed devices to -56.8 dBm for personal/portable devices operating adjacent to occupied channels. To make it easier for devices to comply with these levels, the FCC allowed them to operate with a 0.4 dB higher power spectrum density (PSD) in a bandwidth of 5.5 MHz instead of the full 6 MHz channel.
The FCC rejected a petition from the Wi-Fi Alliance to request a new class of indoor fixed devices that would operate at the same power level as Mode II personal portable/devices and be permitted to operate adjacent to occupied TV channels. While the Wi-Fi Alliance did not specifically address whether this new class of device would have to have geolocation capability, it requested they be classified as fixed devices and the current rules would have given manufacturers the option of specifying professional installation in place of geolocation capability. NAB, Shure and NCTA opposed the petition.
The FCC agreed with the opposition, stating "The Wi-Fi Alliance states that the devices of interest would be mass market Mode II personal/portable devices, thus indicating to us that they would be small and easily transportable. We find that such devices would have a high potential for causing interference to authorized services in the TV bands if they did not incorporate a geolocation capability to accurately determine their location."
The commission further noted that the proposed devices could be easily moved to different locations without updating coordinates, and could therefore receive an inaccurate list of any available channels. The MO&O adds, "In the case of mass market consumer devices, we would not consider the consumer to be a professional installer."
The MO&O is good news for TV band device manufacturers and operators, with them getting increased fixed device antenna HAAT, and also some relief from out-of-band emission limits, especially for very low power devices. It's also good news for other occupants of the TV bands--broadcasters and their viewers and wireless microphone users--whose concerns about increased interference were addressed.
Doug Lung is one of America's foremost authorities on broadcast RF technology. He has been with NBC since 1985 and is currently vice president of broadcast technology for NBC/Telemundo stations.
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