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25th Anniversary of FCC Decision Enabling Wi-Fi and Bluetooth

25th Anniversary of FCC Decision Enabling Wi-Fi and Bluetooth
A series of posts describing how this all came about. (Click on picture above)

Wednesday, November 11, 2009

Unfortunately, You Can't Make

the Wireless Microphone

Problem Go

Away by Taking a Different

Tack in TV White Spaces

There seem to be repeated rumors coming out of FCC that maybe they should take a different approach to utilizing TV "white spaces" by licensing them for broadband. Perhaps some think this will solve the wireless microphone problem painlessly - it won't.

TV white spaces are the inevitable result of TV broadcast licensing, especially when there is uneven terrain and uneven population distribution. There will always be places where there is no usable TV signal on a channel and were lower power use of that channel by other services is possible without interference. Under analog TV there was a lot more such white space due to the "UHF taboos" necessary to avoid neighboring channel interference to TV sets with mediocre selectivity. (FCC efforts in the 1970s to improve TV selectivity and decrease white spaces went down in flames due to broadcaster opposition.)

Wireless mics can use TV white space to provide a useful service, but in doing so inevitably use spectrum inefficiently compared to other possible users of white space. Why? Wireless mic use is intermittent in both space and time and only uses a tiny fraction of the space/time/spectrum resource made available by TV white spaces. Hence use is heavy in the Broadway theatre district of Manhattan and in a few other theatre districts. Use is heavy near churches for a few hours a week. But reserving TV white spaces for the exclusive use of wireless mics denies the spectrum to other that can use it much more intensely.

The current wireless mic mess is a result of both benign neglect of FCC towards this sector and aggressive merchandising by mainly Shure, Inc. to large numbers of users ineligible under current FCC rules to use them. (The hypocrisy of the TV broadcasters for opposing Part 74 eligibility for the churches and theatres for years, if not decades, and then becoming Shure's "best buddy" during Docket 04-186 is certainly a case of "strange bedfellows".)

I have repeatedly written here that "wireless mics are a legitimate use of spectrum (that) deserves more from FCC than benign neglect that allows most users only criminal spectrum squatting" . Yet FCC has taken no action even on the relatively simple issue in Docket 08-166 of evicting wireless mics from the spectrum that is now licensed to others after the DTV transition, let alone the more complex issue in Docket 08-167 of whether action should be taken against anyone for flaunting the Commission's rules and creating a de facto reallocation of spectrum.

The only way to avoid the inefficient use of white space that would result from preserving the present squatting of large numbers of users is to move towards a new method of serving wireless mic needs that does not give them exclusive, hence inefficient, spectrum. Let me note that CMRS licensees already have the regulatory flexibility offer femtocell-like systems that transmit wireless mic signals on CMRS spectrum without interconnection to the public network - one way connections from the microphone to the theatre/church audio panel. While the microphones and analog-to-digital convertors (DAC) used in cell phones are not of sufficient sound quality for many wireless mic applications, there is enough CMRS bandwidth available now to permit adequate quality with better mics and DACs. If the CMRS crowd really wants 800 MHz below 3 GHz , maybe it should seriously think about helping FCC by proposing a practical alternative to the wireless mic impasse.

Another approach to solving wireless mic spectrum problems is to move this use to another band where it will have a compatible spectrum sharing partner. Since wireless mics are a distinctly short range service, such sharing should be possible. For starters, the 1435-1525 MHz aeronautical telemetry band might be considered.

But letting wireless mics just sit in white spaces will inevitably cause problems for both the current policy adopted under Docket 04-186 and any alternative path the Commission might go down.

1 comment:

Henry Cohen said...

A thoughtful and realistic commentary, one with which I generally agree, and I would venture most of my compatriots would as well. Two points though; one minor, one more significant:

1) Shure was hardly the only player in extensive marketing efforts to non-Part 74 eligible users; all wireless microphone manufactures (about a dozen or so) offering [type approved] product in North America participated in what could be construed as questionable target marketing.

2) Although I and my compatriots would happily consider almost any other spectrum to supplement the UHF-TV band for wireless operations, limitations due to physics come into play. Whereas >900MHz is fine for wireless intercom where voice quality is less critical, or cueing where the body worn device is a receiver, this upper spectrum is quite problematic for wireless microphones, especially body packs - the staple of theatrical (Broadway) productions: RF absorption by the human body is tremendous. This comes from years of experience of using STL band equipment and more recently actual field strength measurements. Further, complex stage sets and longer distances render this upper spectrum useless in many situations.

The point is, if consumers of live or live/taped events expect the same level of audio quality they experience today, we'll need to continue to have interference free use of some UHF-TV spectrum, at least until technology improves in as yet an unforeseen scope.