The steady shrinkage of the TV bands is forcing the FCC to look elsewhere for wireless microphone spectrum.

Having inadvertently threatened a key industry with extinction, the FCC is now trying to reactivate it.

We see wireless microphones used on TV stages, live concerts, and in Broadway and Las Vegas shows. TV and film studios use technically similar equipment. So do backstage personnel for intercom and cueing in all of the above productions. Other uses for wireless microphones include public meetings, political events, school and college classrooms, and live music in bars, garage-band garages, and just about everywhere else.

For decades, wireless microphones have operated successfully in locally vacant TV channels. Three recent FCC developments, though, are making those channels scarce. First, the FCC authorized unlicensed TV White Space (TVWS) operation to provide Wi-Fi-type service in many of the same vacant channels. Second, the transition to digital TV eliminated 18 channels from TV use – and also took them away from TVWS and wireless microphones, which greatly increased pressure on the channels that remain. Third, the upcoming “incentive auction” will reallocate still more TV channels to wireless broadband, leaving insufficient spectrum for wireless microphones.

A thick Notice of Proposed Rulemaking takes a long-term view of the problem.

First, it recognizes the importance of wireless microphones in entertainment and in civic and even religious life. Second, it asks for extensive and detailed information on how wireless microphones work and what spectrum they use today. Third, the NPRM goes through a catalog of possible alternative frequencies to the TV bands, asking about the suitability of each for wireless microphones and whether rule changes would help to improve that suitability while still protecting other users. Many of these alternative bands would require the development of technologies not currently used by wireless microphones.

The equipment used for production microphones and performers’ ear monitors has particularly demanding requirements: extremely high audio fidelity with very low latency (throughput delay). Because these requirements are incompatible with significant data compression, these particular devices need relatively high radio bandwidth. Many of the alternative bands suggested by the FCC are too narrow for these critical applications, but may be suitable for other production needs.

Another Notice of Proposed Rulemaking, released the same day, proposes shorter-term solutions for unlicensed wireless microphones.

By order, back in 2010, the FCC established a temporary waiver that has allowed wireless microphones to operate in the TV bands on an unlicensed basis at 50 milliwatts of power (as compared to the 250 milliwatts permitted to licensed microphones). Unlike licensed operation, which is limited to certain categories of users, unlicensed use is open to anyone. The FCC is now proposing to codify this waiver into the rules, which would give the industry a greater degree of certainty than it has now. The proposal includes a few variations from the waiver: adjustments to the required separation from active TV stations; tighter limits on out-of-band emissions; and a somewhat more restrictive definition of “wireless microphone.”

After the incentive auction, there will be 3 MHz guard bands around channel 37 (which is used for radio astronomy and medical telemetry), a guard band of as-yet-unknown size between the surviving TV frequencies and the new wireless broadband allocation, and an 11 MHz “duplex gap” between the downlink and uplink segments of the broadband spectrum. The NPRM proposes to allow unlicensed wireless microphones to operate in some of each of these, but at only 20 milliwatts: in 2 MHz of each channel 37 guard band, in all but 1 MHz of the TV/broadband guard band, and in 6 MHz of the duplex gap, shared with TVWS devices. (Another 4 MHz of the duplex gap is set aside for licensed wireless microphones.)

But there is a complication. The Spectrum Act – the statute that authorized the incentive auction – says: “Unlicensed use shall rely on a database or subsequent methodology as determined by the Commission.” TVWS devices “rely on a database” without question: each individual device must communicate with a database that identifies safe operating channels at that particular location and time, or must communicate with another device that does. Wireless microphones do not have this capability, and have never needed it; users and their coordinators pick channels manually, according to local conditions, and over the years have caused essentially zero interference to other users.

The FCC is particularly concerned about the transition period following the auction, when future guard band frequencies, those that will later be open to wireless microphones, are still functioning as TV channels that wireless microphones must not use. Making matters worse, that transition will proceed unevenly around the country. Frequencies that have completed the shift to guard-band status in some places may still be in use for TV broadcasting in other places, making it more difficult for wireless microphone users to keep track. One option is to require that unlicensed wireless microphones check in with the TVWS database before transmitting at a given location. Providing the capability for automatic checking, however, would add to the products’ complexity and cost. The FCC asks whether it would satisfy the statute for the user to manually check a database using a laptop or a smartphone.

Also for the transition period, the FCC has set minimum separation distances between wireless microphones and operating regions of the incoming wireless broadband providers. The same question arises on how wireless microphone users will determine whether operation is allowable at a particular time and place.

Comments are replies for each NPRM will be due 45 and 65 days, respectively, after it appears in the Federal Register. We will let you know.