The Federal Communications Commission on Tuesday asked for proposals from those that want to coordinate frequencies in the 6 GHz band for standard-power unlicensed devices to avoid interference with incumbent users.
It comes less than two weeks after the regulator and AT&T faced off over unlicensed use in the 6 GHz band in oral arguments before the U.S. Court of Appeals for the D.C. Circuit.
Automated Frequency Coordination (AFC) was a topic that came up in AT&T’s appeal of the unanimous FCC decision and 2020 order that opened 1,200-megahertz of spectrum in the 6 GHz band for unlicensed users including Wi-Fi.
In a public notice (PDF) issued this week ahead of the commission’s open meeting, the FCC initiated the process for authorizing AFC systems in the 6 GHz band and adopted the item during circulation.
“This item is another step towards fully unleashing the potential of the 6 GHz band, by beginning the process of authorizing Automated Frequency Control (AFC) system operators to offer their services to parties seeking to operate in certain portions of the 6 GHz band outdoors at standard power levels,” said FCC Commissioner Geoffrey Starks in a statement. “Through such AFC systems, standard power unlicensed devices will be able to coexist in the 6 GHz band with incumbent fixed microwave links and radio astronomy observatories. I look forward to reviewing the applications and continuing our progress in making unlicensed spectrum available on a noninterference basis.”
The move received cheers from the WifiForward Coalition and WISPA.
Federated Wireless is one party that’s expressed interest in and previously pointed to work on AFC for the 6 GHz band. Federated already is one of five FCC authorized Spectrum Access System (SAS) administrators for the shared Citizens Broadband Radio Service (CBRS) band.
The FCC can designate one or more AFC system operators, which would be required to serve for five years and could then be renewed based on performance.
Interested parties can submit initial proposals by November 30, 2021, with comments due by December 21.
AFC for low-power devices?
While the FCC is looking for proposals for AFC to mitigate interference with fixed microwave links from standard-power devices in the 6 GHz band, AT&T recently continued its court battle.
On September 17, lawyers for AT&T told a three-judge panel that the FCC had no reason not to require the same AFC technology for low-power devices, like indoor Wi-Fi routers and access points, operating in the same spectrum to avoid what it claims is very likely harmful interference with fixed microwave links.
The fight from AT&T and others, including APCO (The Association of Public Safety Communications Officials International), is not new – with concerns raised throughout the 6 GHz proceeding and the D.C. Court of Appeals in October denying motions to stay the FCC order. AT&T originally filed a petition challenging the FCC on 6 GHz in June 2020.
The FCC has had heavy hitters show up in support led by Apple, as well as Broadcom, Cisco, Google, Intel, and Microsoft.
The carrier was a license holder for fixed services that support mobile backhaul and telecom landline, but the 6 GHz band also supports microwave links for public safety and critical infrastructure.
During oral arguments, Jonathan Nuechterlein, attorney for AT&T and APCO, called the FCC’s decision not to require AFC for low-power devices “a mystery.”
“The FCC had an opportunity in this order to get everything right, could’ve opened up the 6 GHz band for Wi-Fi while protecting public safety, the power grid and other licensed uses. Specifically, as the NPRM [Notice of Proposed Rulemaking] itself proposed, the FCC could have required all unlicensed devices that share spectrum with fixed microwave links to use automated frequency coordination, also known as AFC,” the attorney said. “An effective AFC mechanism would minimize interference risks by keeping these devices from transmitting on the same frequencies as nearby microwave links.”
He claimed the FCC order doesn’t identify any drawbacks to what the agency said is simple and easy to implement for standard-power devices, or that it would add significant cost.
During the hearing, circuit judges noted that the Commission said the order was designed to prevent against the risk of significant, but not all interference – quoting that “harmful interference would be a rare but possible occurrence.”
AT&T, on the other hand, argued that there is more than an insignificant risk.
AT&T said it showed “that it is very very likely that at some point over the next 10 years some of these billion-odd devices will interfere with some of the 100,000 microwave links” and that the government wasn’t giving a clear position on its response to that.
AT&T is also concerned as Wi-Fi devices with support for the 6 GHz band are starting to come onto the market now and argued one device like a Wi-Fi router without AFC could interrupt signals on a microwave receiver – including links responsible for preserving power grids and first responder communications.
The FCC, a judge noted, said if harmful interference does occur, the commission has the legal authority to step in and stop it. However, AT&T said it’s a different context where steps after the fact don’t help.
“If one of these links go down, the harm for that day is already done and there will be 911 calls that won’t go through, there will be failure to communicate with nuclear power reactors…that’s the concern we have here,” AT&T argued. “Again, all of these concerns could be mitigated significantly by imposing this AFC requirement.”
Attorneys for the FCC pointed to disturbances in the atmosphere that could make microwave links lose power and degrade from low power devices, but without these fading events - called deep atmospheric multipath fade – which they said don’t occur often, low-power devices won’t really interfere.
The FCC told the three-judge panel that AT&T provided a “worst-case” analysis and that it’s unlikely low-power access points or routers could interfere with powerful point-to-point microwave-based transmissions.
Judges raised questions about technical aspects of interference, as well as the robustness of studies relied on, including one from CableLabs that used data points in New York City. They questioned if it could be representative for interference in vastly different geographies across the country.
During oral arguments, one of the judges pointed to AFC as one of three ways the FCC may have acted arbitrarily and capriciously, if it failed to address why the technology wasn’t a better choice than other steps the commission described taking instead.
The FCC again argued it was because the technology isn’t necessary for low-power devices since there is insignificant risk of harmful interference.
A judge asked if the court disagreed with the FCC, why the order should be remanded back to the regulator for clarifications rather than thrown out altogether.
“Vacating this order would be incredibly disruptive given the fact that devices have already started to be deployed,” said attorney James Carr for the FCC, adding that if the court wanted more explanation, the FCC is in a position to provide that.