The FCC has released a Notice of Proposed Rule Making (NPRM) and Order regarding Facilitating Opportunities for Flexible, Efficient and Reliable Spectrum Use Employing Cognitive Radio Technologies. The rules proposed in the NPRM and Order would not have any immediate impact on most broadcast RF operations, although the cognitive radio technologies described in it could ultimately be used to allow sharing of any part of the RF spectrum, including the broadcast bands and broadcast auxiliary spectrum. For an overview of the technology, see RF Report for Dec. 22.
One of the major changes proposed by the NRPM and Order is allowing unlicensed frequency hopping systems authorized under Section 15.249 of the FCC rules using the 902-928 MHz, 2400-2483.5 MHz and 5725-5850 MHz to operate with up to 6 watts transmitter power. These systems would need to employ a minimum number of frequency hopping channels (except in the 5.8 GHz band) and have transmitter power control circuitry that would limit power to the minimum level required for reliable communications. In addition, high power operation would be limited to areas where spectrum use was low. The systems would be required to have cognitive technology to sense spectrum use before commencing transmissions. Unlicensed operations governed under Section 15.249, which specifies field strength, would also be allowed to increase power if they have cognitive technology to sense spectrum use. Field strengths in the 900, 2.4 and 5.8 GHz band would be increased to 125 millivolts per meter at a distance of 3 meters and up to 625 millivolts per meter at 3 meters distance in the 24.0 to 24.25 GHz band.
For defining areas with limited spectrum use to allow the higher power operation, the FCC proposes to define "unused spectrum" as spectrum "with a measured aggregate noise plus interference power no greater than 30 dB above the calculated thermal noise floor within a measurement bandwidth of 1.25 MHz, which is the same value specified for unlicensed PCS devices." The NPRM asks for comments on the implications of adopting this definition, including the possibility that high power devices could block the use of lower power devices. For example, the NPRM asks "whether a device operating at higher power should have to re-sense spectrum use at periodic intervals to determine whether other users are attempting to transmit. If so, how often should it re-sense? Would such a requirement have undesirable effects, such as requiring a WISP to lower power or turn off completely, and possibly lose a connection when another device such as a cordless telephone comes on the air, or causing users of lower power devices to simply cease operating if they received interference?" Possible alternatives to sampling spectrum use include uses of GPS to allow a device to determine if it was in a rural area or a combination of the two approaches.
There has been much discussion about the ability of cognitive radios to use spectrum allocated to other services (including Public Safety) when the spectrum isn't being used. The NPRM outlines a system where a beacon transmitter would be used to notify cognitive radios that the spectrum was available. If the beacon wasn't received, then the cognitive radio would have to assume the frequency was in use and avoid it. Beacon transmissions would be encoded/encrypted to define what radios could use the frequencies and to prevent piracy.
Cognitive radios offer opportunities for greater spectrum efficiency and possible subleasing of licensed spectrum for secondary uses. This technology will likely have an impact on the frequencies broadcasters use now and may open up new frequencies for broadcasters (and others) to use. The 53 page Notice of Proposed Rule Making (NPRM) and Order outlines the proposed rules and equipment certification requirements and provides a brief tutorial on some of the most promising cognitive radio technologies.
