DTV Audio Group Wraps Series of Meets on Spectrum Ideas

By Dan Daley, Audio Editor, Sports Video Group

The DTV Audio Group held a series of meetings in June, between constituents and stakeholders in the impending auction-based reallocation of RF spectrum, and with the FCC and its Office of Engineering Technology (OET), to present ideas on alternative spectrum assignments for licensed users of professional wireless microphones.

“The main thrust for all of these meetings has been to review the alternative spectra referenced in the Notice of Proposed Rule Making (NPRM) 14-166, evaluate their feasibility, and determine the practical and regulatory obstacles to make use of them in the future,” DTVAG Executive Director Roger Charlesworth told SVG. “What’s already on the table is not going to be enough. Ultimately, we will also have to identify more spectrum and develop further technologies to make what we have work as efficiently as possible.”

The first meeting, which took place on June 12 at Fox Networks’ New York headquarters, included representatives from all four major networks as well as wireless-microphone and communications system manufacturers Audio-Technica, BSI, Lectrosonics, Radio Active Designs, Sennheiser, Shure, and Sony in addition to representatives from the Society of Broadcast Engineers and various frequency coordinators and other solution providers.

The five-hour meeting examined alternatives to the 600-MHz frequency range that will become unavailable to users of professional wireless systems after the spectrum auction and subsequent re-allocation to wireless carriers is complete, scheduled to take place in in 2016. These alternatives include expanded use of upper UHF bands in the 941-MHz to 960-MHz range, as well as frequency ranges between 1435 MHz to 1525 MHz, and 2020 MHz to 2025 MHz and parts of the 6875 Hz to 7125 MHz BAS bands.

Charlesworth said that the FCC’s OET wanted more specific information about how these bands could be used, what safeguards might be put in place to protect incumbent users, which afforded the best short-term potential, and how much additional spectrum wireless users would need and what areas they thought might be promising for further development.

“We also discussed VHF and other low-frequency ranges that are already being used for comms and the potential for extending their use,” he explained. “Short-term, the 941-MHz to 960-MHz range, which is now used for studio transmitter links and some microwave uses, will likely need to be part of the solution. The 1435 MHz-to-1525 MHz range is allocated for aeronautical telemetry and it is already also used, with special temporary authority, for some wireless camera applications and in some cases wireless microphones. European [wireless] microphone manufacturers already make products in that range, but they would have to add capability for geolocation-awareness and transmitter-to-receiver tethering to ensure that expanded use would not interfere with incumbents.”

Even a solution like that would only work robustly in areas like New York City, where aeronautical testing is rare. In areas like Southern California or even Wichita Kansas, which have bustling aviation industries, those frequencies would be of far less use.

“There are a number of promising solutions, but they’re all encumbered in one way or another,” Charlesworth said.

Charlesworth noted that the process really started in 2010, with the loss of the 700-MHz frequency band, when wireless users struggled to find other parts of the spectrum they could utilize or make more productive (including, at the time, the now-doomed 600-MHz band). “The problem now is that all of the remaining alternatives are either in some way impaired or have other incumbents or both,” he said.

Part of the solution will have to come from enhanced technology. Charlesworth noted that the latest wireless microphone systems have dramatically improved spectral efficiency. “If we can find even an extra five MHz of clean spectrum, we may be able to get another 50 channels in there,” he estimated. “Ultimately, manufacturers may also have to develop products that operate in the less-desirable higher bands above 10 GHz to make up for what we’re losing.”

The meeting with the Spectrum Auction Task Force on June 18, wasn’t cause for optimism and raised concern that some accommodation for wireless microphones in a portion of the so-called “duplex gap” — specifically 4 MHz of spectrum in the 600-MHz range between uplink and downlink operations — may be impaired if the FCC is forced to use of some of that space for television stations. In some geographical areas, like Southern California and along the US-Mexican border, there may not ultimately be spectrum available in the duplex gap to permit reliable wireless use on short notice, such as for breaking news broadcasts, as had been hoped.

On June 22, representatives from the June 12 DTV AG meeting met with FCC chairman Tom Wheeler and later with Julius Knapp, chief of the OET, and members of his staff. Charlesworth said that they laid out their conclusions on alternative spectra, their pros and cons, and urged the FCC to act quickly on rule making to allow access to some of these alternate bands.

“We talked about the details of the suggested bands. It would be great if the FCC could move quickly, as it will take manufacturers time to develop product and get it into production,” said Charlesworth, who characterized the meetings as “extremely productive.”

This second major loss of spectrum in less than a decade is obviously hard on wireless audio users, including broadcasters. The fact that they’ve been through this search for alternatives before is of little comfort because there’s that much less usable RF real estate to look to for solutions this time. The pressure is apparent from Charlesworth’s observations that professional wireless users “make good neighbors” because broadcast operations and other professional use is closely coordinated and users tend to be mindful of rules and regulations, a selling point to incumbent spectrum users to encourage sharing of their airwaves. It’s an environment in which any solution, no matter how convoluted its execution may prove to be, is considered seriously.

“The reality is that the future is going to be made up of bits and pieces from here and there within different parts of the frequency spectrum,” says Charlesworth, “and it’ll all have to be shared with someone else.”

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