Full speed ahead for contested 5G, W-Fi spectrum

Recent wrangling over 5G and Wi-Fi wireless spectrum indiates the breakneck pace of new bandwidths being opoened up to broadband use will continue.

The underlying issues are whether newly alloted 5G bandwidth will interfere with airplane safety and whether new unlicensed spectrum will interfere with the backhaul of communications from cell towers.

Airlines vs. telecoms

The FAA’s well-publicized worries over 5G deployments in the recently auctioned C-band frequencies center on the potential of those 5G services to interfere with radio altimeter equipment in older aircraft. A radio altimeter is an avionics device that measures the distance between the bottom of an airplane and the ground directly, using radio waves, rather than measuring the surrounding air density like barometric altimeters do. It’s a key technology for bad-weather and low-visibility landings, and the possibility of any interference with those systems is worrisome from a safety perspective.

Older radioaltimeters function at around 4.2GHz, while the C-band spectrum sits at roughly 3.7GHz – that should provide a reasonably-sized guard band to prevent the two systems from interfering with one another, but the FAA remains concerned. Regardless of how unlikely an interference issue is, it does represent a potentially serious safety problem, according to Forrester vice president and research director Glenn O’Donnell.

“There are tech solutions to try and protect against [interference] but there is potential for wreaking havoc on some of these systems,” he said. “So if one of the carriers has a 5G service that could be interfering with aircraft, that’s a big deal.”

That said, experts agree that neither the airlines nor the FAA has produced definitive evidence that the C-band spectrum auctioned off by the FCC for use by carriers would impinge on those systems.

“I haven’t seen anything yet that has shown, in a real-world scenario, that this kind of interference could affect the ability of an airliner to land safely,” said Gartner Research analyst Bill Menezes.

Moreover, the position of the wireless industry is that the writing has been on the wall for C-band usage for some time, and that the aviation sector has had years to prepare for this eventuality. Similar frequencies have been used for broadband in other countries, most notably France, with no aviation safety issues, Menezes noted.

After initially balking at the FAA and the Department of Transportation’s suggestion to delay C-band deployments near major airports, AT&T and Verizon agreed last week to hold off for two weeks, and to reduce the transmission power of their 5G base stations near airports.

Tussle over 6GHz

The D.C. Circuit Court of Appeals’ decision earlier this month to uphold the FCC’s opening of a whopping 1,200GHz of new spectrum in the 6GHz range for unlicensed–read: Wi-Fi–confirms that the future of Wi-Fi 6E is safe.

AT&T had filed suit in opposition to the 6GHz decision, arguing that it carried an undue risk of interfering with established fixed-service links on nearby bandwidths that needed to provide network backhaul for cellular sites. The dispute had been an ongoing since the decision was announced in April 2020.

Part of the reason that the matter escalated to the level of a lawsuit is that 6GHz spectrum, the Goldilocks spectrum, is both high-frequency enough to support large channels and consequently high data rates, and also low enough to propagate well over distance, according to O’Donnell.

“AT&T have a lot of links they use for lots of things, including backhaul, and 6GHz is a popular place to put some of those things,” he said.

The court’s holding largely deferred to the FCC’s contention that the risk of interference with existing links is minimal, though not non-existent, thanks to restrictions on the signal strength of outdoor devices and advances in interference-mitigating technology.

The commission’s push to open more spectrum for data services is largely in keeping with its role as the governing body for America’s airwaves, said Menezes.

“Remember that the FCC…responds to industry requests for more spectrum, and the biggest industry requests for the last decade or more have been coming from the wireless communications industry,” he said. “Part of the FCCs responsibility is to ensure that spectrum is used responsibly and effectively, not lying fallow while there’s a public good that could be realized with it.”

Other stakeholders remain skeptical of the speed at which the FCC has thrown open large amounts of wireless spectrum to broadband services, according to O’Donnell.

“My personal viewpoint on this is that the FCC is pandering too much to the carriers,” he said. “There’s just an enormous amount of money being spent on spectrum auctions, and if you’re a public service…there’s just no money there.”