Public-safety microwave systems—considered by many to be the “backbone” of mission-critical LMR networks—already are being harmed by the introduction of unlicensed uses in the 6 GHz band, and the problems could worsen in the future, according to a member of APCO’s governmental-affairs team.

Mark Reddish, senior counsel for the Association of Public-Safety Communications Officials (APCO), said APCO strongly opposed the FCC’s 6 GHz order that allowed unlicensed uses in the band, but those efforts proved to be unsuccessful, as did a lawsuit that attempted to reverse the FCC’s rules for the band. As feared by many in public safety, even the lower-powered routers at 6 GHz have created issues for mission-critical communications, he said.

“This is a very hot topic in the community, because—right now—the devices are relatively new routers,” Reddish said during a session at the APCO 2023 event in Nashville, Tenn. “They can use so much more spectrum than the old type of device, so I really think there’s going to be a hockey-stick [shaped] growth in the penetration of these devices.

“And the more that are out there, the more problems there are going to be for microwave system in public safety.”

This is particularly troublesome for the public-safety community, because the 6 GHz spectrum band is widely used for microwave links that are key components in a number of mission-critical systems, according to Reddish.

“It’s used in the public-safety community for microwave links for backhaul—the backbone of public-safety communications,” he said. “We have microwave supporting our LMR networks’ first-responder radio comms. We have microwave networks connected ECCs to one another for backup. So, it’s critically important spectrum supporting these links.”

On the surface, consumer-grade unlicensed wireless routers might not seem to be an interference concern for mission-critical communications systems, but Reddish noted that public safety and other incumbents built their systems with idea that they would have exclusive use of the 6 GHz spectrum, as was the case when most microwave links operating in the band were established.

“Keep in mind that these [6 GHz microwave] systems had not, up until this point, needed to be designed to resist interference from a device operating on the exact same channel, because these were all exclusively licensed systems,” Reddish said.

While some “edge cases” of unlicensed 6 GHz use may interfere harmfully with public-safety communications directly, Reddish expressed greater concern about the “aggregate effect” of unlicensed devices being deploy, which potentially could compromise the resiliency of mission-critical microwave systems during the most challenging of circumstances, such as an extreme-weather scenario.

“Basically, when you get a few things going wrong at the same time—including operation of these [unlicensed] devices—that’s when you are really at risk of a significant interference event,” Reddish said.

With this in mind, APCO issued a technical bulletin urging operators of 6 GHz microwave systems to test and measure the performance of the links as soon as possible, so that data can be used as a baseline test if unlicensed use is suspected as a cause of degraded performance in the future, Reddish said.

Today’s lower-powered 6 GHz unlicensed Wi-Fi routers—supposedly designed only for indoor use—are creating some problems for public safety, but there are other threats looming in the band. Powerful corporations like Apple, Google and Meta are leading the push for the FCC to allow the use of higher-powered 6 GHz unlicensed devices outdoors, subject to automatic frequency coordination (AFC) system, which uses a database to inform devices where incumbent system are located in an effort to reduce the likelihood of interference.

Reddish expressed concern with the AFC approach.

“This is really an unproven framework, and we’re in the throes right now of figuring out what the final authorization is going to look like for those types of devices,” Reddish said. “But we already have the lower-powered type of device out in the the field, and there is evidence that they’re causing problems today.”