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White Space Impact on Wireless Audio

While the transition to digital television is a big story, there are smaller but no less important stories being pulled along in its wake. One of particular interest to AV pros is that of white space and its impact on wireless audio.

While the upcoming transition to digital television (Feb. 17, 2009) is a big story, there are smaller but no less important stories being pulled along in its wake. One of particular interest to AV pros is that of white space and its impact on wireless audio. Quick refresher on white space: Technically speaking, white space is any unused frequency (or range of frequencies) in the television spectrum that could also be put to work for various wireless consumer electronic devices, such as home media networks and wireless bridges. All would use low-power emissions to transmit and receive signals over short distances—say, around a home and across the yard.

Wireless consumer transmitters have been around for decades, going way back to the phono oscillators of the 1950s and “toy” radio stations of the 1960s and 1970s. (I operated one of each on AM and FM during my formative years.) Their operation is clearly governed under Part 15 of the FCC's rules.

In a nutshell, these rules—which pertain to unlicensed, low-power transmitters and receivers (known as “restricted radiation devices” early on and “intentional radiators” now)—clearly state that Part 15 devices have no protection against interference from licensed transmitters, must accept interference from those sources, and cannot interfere with licensed transmitters or the reception of their signals.

Sounds pretty straightforward, doesn't it? Ah, but white space is also used extensively by manufacturers and users of wireless microphones, particularly channels in the UHF television band (channels 14–69, or roughly 470 MHz to 800 MHz). Wireless audio co-location requires frequency coordination to ensure that TV broadcasts and other wireless audio sources don't interfere with each other.

The current system of licensed and unlicensed wireless audio coordination has worked exceptionally well and is supported vigorously by wireless microphone manufacturers. So you can imagine their skepticism when the likes of Microsoft and Philips showed up, claiming they could manufacture and implement low-cost consumer white space products that were frequency agile, sensitive enough to detect existing TV and wireless audio transmissions, and smart enough to stay out of their way. (For more background, see Consultant's Connection, February 2008).

The FCC's Office of Engineering Technology (OET) had its doubts, too, which were confirmed by two sets of tests conducted in 2007. In both tests, prototypes of white space device failed to detect weak, sustained analog and digital transmissions (simulating analog and digital TV broadcasts) and short duration transmissions (simulating wireless microphones).

In fact, the performance of these prototype devices was so bad that one manufacturer was compelled to offer an excuse in the form of “power supply issues.” Additional comments from the Association for Maximum Service Television and the National Association of Broadcasters followed, urging that the FCC not adopt rules for white space devices that would interfere with TV broadcast and wireless audio use at major sporting and non-sporting events.

This past July, the FCC decided to revisit the issue with a new round of tests, but this time they took place away from the OET laboratories. The field locations included Patapsco Valley State Park in Elkridge, Md., and the Baltimore-Washington International Airport, along with multiple private residences.

Another key part of the test took place during an NFL pre-season game between the Buffalo Bills and Washington Redskins at FedEx Field in Landover, Md, on August 7. According to news reports from the Sports Video Group, the white space devices tested failed to detect existing analog and digital TV broadcasts on occupied UHF TV channels, and they “also failed to detect the presence of wireless microphones when switched on, an occurrence that takes place multiple times during any NFL game.”

That's a pretty damning indictment, and it demonstrates that little or no progress has been made to improve the design of white space products in over a year. The FCC's tests continued into August at a number of residences in the Washington, D.C., area. As of this writing, no results had been made public.

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