03.09.2007 12:00 AM
NAB/MSTV Reply Comments Cite Danger of Unlicensed Devices
If you view off-air TV, are a TV broadcaster, or are a user of wireless microphones, you should devote an hour or two of your time to reading the Joint Reply Comments of the Association for Maximum Service Television Inc. and the National Association of Broadcasters in ET Dockets 04-186 and 02-380 regarding unlicensed operation in the TV broadcast bands. The Joint Reply Comments make a strong case for allowing NO unlicensed personal/portable devices in the TV broadcast spectrum. They provide an easy to understand technical argument showing that both strict limits on out-of-band emissions and protection of co-channel, adjacent channel and taboo channel frequencies are needed within a TV station's DTV service contour to protect reception. And, as cable headends sometimes receive TV signals beyond a station's service contour, additional protection may also be needed.

The main argument against personal/portable unlicensed operation in the TV bands is based on the fact, as carefully outlined in the Joint Reply Comments, that signal sensing technology is not adequate to protect TV reception. NAB and MSTV show that with a wide range of devices operating at powers of 100 mW on TV channels, the proposed sensing receiver sensitivity is insufficient, after considering the low gain and low elevation of the sensing antenna compared to an outdoor TV antenna. Only geolocation will ensure that devices operating in the TV band will not cause interference to reception, and even that will depend on the database of operating TV stations being kept up to date.

The Joint Comments indicate that if geolocation technology is used, required interference protection ratios are correct, devices are licensed, and installed by professionals, they may be able to operate in the TV bands without causing interference. Several of the arguments in the Joint Reply Comments cite the University of Kansas study that was conducted for New America Foundation, a supporter of opening TV "white spaces" for unlicensed operation. NAB and MSTV are pushing for stricter limits on out-of-channel emissions and use of the correct interference ratios, based on that report's findings.

NAB and MSTV point out that many of the proponents of operating unlicensed personal/portable devices in the TV bands without harm do not provide any technical analysis to support their position. Yet comments from both proponents of fixed broadband wireless systems operating in the band and broadcasters arguing for stricter interference protection do provide such data.

A new concern raised is that new mobile/portable DTV receivers utilizing more robust transmission methods, such as the A-VSB system and the system recently announced by Harris Corp., will allow reception at levels below the theoretical ATSC 15 dB signal to noise ratio. This means that devices operating inside a TV station's service contour can't count on interference-free operation if the interference analysis does not include the potential for new DTV services which could be received at signals at levels lower than those described in the FCC planning factors.

There is far too much information in the Joint Reply Comments of the Association for Maximum Service Television Inc. and the National Association of Broadcasters to cover in this newsletter. I've only hit a few of the concerns expressed by NAB and MSTV.

Use the FCC's search for filed comments Web page to see the other comments filed in this proceeding. Enter "04-186" in box one. In the results of the search, you will see comments from Shure on the problems transmitters on unoccupied TV channels will cause for the large number of users of wireless microphones. You will also see the comments of numerous broadband service providers as well as comments from potential manufacturers of devices for use on the TV band. Of course, in addition to the Joint Reply Comments from NAB and MSTV, many other broadcasters filed comments voicing their concerns.


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