WMAS Technology Aims To Fit More Into Less Spectrum

WMAS Technology Aims To Fit More Into Less Spectrum Post-FCC auction search for more-efficient use of remaining spectrum enters another phase By Dan Daley, Audio Editor

Wednesday, May 3, 2023 - 7:00 am

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If you were to look for a definition of WMAS online, you'd encounter links to home pages for Tennessee Wildlife Areas, the Watershed Management Authorities in Iowa, or an Adult Contemporary FM station in Springfield, MA, before you found a reference to Wireless Multichannel Audio Systems. Even so, according to stakeholders in the RF universe, the technology could be a game-changer for managing wireless signals in a narrower, denser spectral environment.

WMAS technology, already an ETSI standard in Europe, allows dense multiplexing of audio channels onto a single wideband RF carrier, offers an easier and more flexible wireless workflow, and provides greater protection to other services sharing the same frequency band.

Specifically, WMAS would let wireless users operate in a wider bandwidth than Federal Communications Commission rules currently allow, enabling more wireless microphones to operate in that spectrum.

WMAS has been on the FCC's radar for more than four years, with wireless-systems manufacturers recommending various ways to approach its regulation in the U.S. In April 2021, the agency issued a Notice of Proposed Rule Making (NPRM) asking for public comment.

Efficient Use of Shared Spectrum The goal of the technology is to more effectively and efficiently utilize existing available RF spectrum without impacting the spectrum rights of other authorized users, such as broadcast licensees, white-space-device users, or current wireless-microphone users that share the frequency bands with wireless-microphone operations. Among other things, what WMAS proponents seek is authorization to use 6-MHz channels when available, such as a locally vacant UHF TV channel or in the 657-663-MHz segment of the 600-MHz duplex gap, with at least three audio channels per megahertz of spectrum to ensure that the spectrum is used efficiently. To accomplish this, the FCC would have to agree to revise its existing Part 74 and Part 15 wireless-microphone technical rules to reference relevant portions of the 2017 ETSI wireless-microphone standard. Hence, the NPRM.

The NPRM came about as a result of a petition for rulemaking filed in August 2018 by Sennheiser, requesting that the FCC define a new class of wireless microphone called a Wireless Multichannel Audio System (WMAS) that digitally combines the signals of multiple low-power auxiliary station devices into one radio-frequency channel. Sennheiser requests that such systems be permitted to operate with a maximum channel bandwidth of 6 MHz, rather than 200 kHz as the rules currently allow, and that they be permitted to operate in the TV bands, the 600-MHz duplex gap, and in the 941.5-944-MHz, 944-952-MHz, and 1435-1525-MHz bands.

If signals from multiple devices are digitally combined into a 6-MHz RF channel, according to Sennheiser's proposal, intermodulation issues would be eliminated, denser use of the spectrum would be permitted, and power density across the channel would be reduced.

Sennheiser's Joe Ciaudelli: [WMAS] is only part of the equation in addressing the needs of content-creation professionals. [As with] any wireless device, access to suitable spectrum is required.

Sennheiser's proposal differentiates between two types of devices: microphones and in-ear monitors (IEMs), which require the highest possible audio quality and lowest latency and currently use a 200-kHz channel; and intercom and IFB systems, which can tolerate limited frequency response and dynamic range as well as some distortion and latency and currently operate in a 25-kHz bandwidth.

It's a big ask, though not a novel one: in Europe, WMAS is already permitted under applicable European Telecommunications Standards Institute (ETSI) standards.

We applaud that the commission seems to be entertaining our Petition for Rulemaking to authorize WMAS, says Joe Ciaudelli, director, spectrum and innovation, Sennheiser, but it's only part of the equation in addressing the needs of content-creation professionals. [As with] any wireless device, access to suitable spectrum is required. Sennheiser will continue to work with the commission on developing long-term solutions.

The company is joined in endorsing WMAS by other wireless-systems manufacturers, notably Shure, which with processing developer Waves, jointly submitted an ex parte filing to the FCC that reaffirmed their backing of WMAS but also noted differences in their applications from those of Sennheiser.

We worked with incumbents in the TV-UHF band, the primary spectrum band for wireless mics, to alleviate any concerns they may have, especially with the unlicensed use of WMAS, explains Prakash Moorut, global head of spectrum and regulatory affairs, Shure. The majority of our users operate wireless mics without a license, and we view FCC allowing unlicensed WMAS a must,' even if it means putting some additional constraints on unlicensed WMAS.

Shure's Prakash Moorut: We view FCC allowing unlicensed WMAS as a must.'

To illustrate its points, in June 2022, Shure, with the support of NAB and Paramount Global, conducted a demonstration at New York's Ed Sullivan Theater (which is owned by CBS, part of the Paramount brand) to illustrate the co-channel and adjacent-channel impact of WMAS systems on conventional analog and digital narrowband wireless-microphone systems. The outcome, according to Shure, demonstrated that operating a legacy narrowband wireless microphone in the adjacent channel of a WMAS signal was successful in a real-world scenario. However, Shure also demonstrated by using a 2-MHz and 6-MHz WMAS signal tha

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