Shrinking Spectrum, Expanded Uses
The amount of spectrum available to broadcasters is shrinking. TV Channels 52 through 69 are being reallocated to other services and the 2 GHz broadcast auxiliary band is losing 30 MHz. Meanwhile, new technology is being developed to allow for use of the remaining spectrum for purposes other than broadcasting.
Broadcasters are facing the imminent loss of the two lower channels of the 2 GHz broadcast auxiliary band. This is the band most commonly used for newsgathering and in many TV markets all channels are packed. As described in the Nov. 17 RF Report
, in the top 30 markets the five remaining channels will split back into seven channels by reducing the channel width to 12 MHz and setting aside two 500 KHz segments of 20 25-KHz wide data return link (DRL) channels each. The DRL channels should allow more efficient use of the existing spectrum and could possibly be combined with other technology to enable real-time frequency coordination.
To maintain the same video and audio quality, broadcasters using these narrower channels will have to switch to digital modulation such as COFDM. In the top 30 markets, the new occupants of the lower two channels -- the mobile satellite service and advanced wireless service -- will be required to cover the cost of the conversion to the narrow channels for broadcasters who had licenses on these channels before they were reallocated. How costs will be defined, however, will be decided in negotiations.
In addition to the reduced spectrum for 2 GHz broadcast auxiliary links, the Society of Broadcast Engineers
is fighting use of this spectrum by high power Department of Defense uplinks. See the Nov. 17 RF Report
for more information on this.
By this time most broadcasters know Channels 52 through 69 have been reallocated for other services. Some of these services may start moving into vacant channels in this spectrum before all broadcasters leave. The FCC is setting rules to minimize interference between the new services and broadcasters, but it is possible broadcasters on channels adjacent to the new services may be required to install extra filtering or take other steps to reduce interference to them. These restrictions could also be applied to future DTV operations on Channel 51 after the transition.
While broadcast spectrum is being squeezed, new opportunities are opening up to share spectrum -- including broadcast spectrum -- using new technology such as radios that can sense the interference environment (either directly or through communication with other radios or a monitoring point) and take advantage of unused spectrum. The FCC is planning to test this technology in the 6.5 GHz and 13 GHz bands and has suggested that broadcast TV spectrum could also be used. The technology is already being used in 5 GHz U-NII radios. As noted in the previous article, New Options for News Gathering, broadcasters should be able to take advantage of this unlicensed spectrum for various applications.