Adding to the voices calling for the FCC to leave the 6 GHz band well enough alone is AT&T, which says the band contains about 100,000 microwave links, many of which are carrying critical voice and data traffic, including for the nation’s first responders.
Representatives of AT&T, which won the contract to provide the network for FirstNet—the nation’s first nationwide wireless network dedicated to public safety—met last week with FCC staff to discuss its concerns about a proposed expansion of the 5.9125-7.125 GHz band to include unlicensed use. AT&T said it will be relying on a significant number of existing and newly developed 6 GHz fixed links in support of FirstNet, where it’s contractually obligated to provide high levels of reliability.
AT&T’s input, made public in an ex parte filing, comes on the heels of the Fixed Wireless Communications Coalition’s comments blasting a report by RKF that was intended to demonstrate that it would be OK to share with existing fixed service microwave users in the 6 GHz band. That RKF report was submitted on behalf of some very well-known tech names, including Apple, Google, Cisco Systems, Facebook, Qualcomm, Intel and Microsoft.
According to AT&T, about 25% of the links in the 6 GHz band support public safety and critical infrastructure industry licensees, and about 27% of the links in the band support utilities, making the upper and lower 6 GHz bands key in supporting the nation's critical infrastructure. It also said that maintaining long-haul and high-reliability microwave links will be critical for 5G and other advanced services.
“Recent filings have identified a number of flaws in the RKF Study that call into question the feasibility of unrestrained sharing in the 6 GHz band between unlicensed services and existing users,” AT&T said in its presentation (PDF).
AT&T shared that its use of radio local area networks (RLANs) for LAA in the 5 GHz band shows that virtually all are operating at the highest allowable power, and most are operating at heights of 30 feet. AT&T also believes RKF underestimates growth in outdoor RLANs; AT&T has 200 RLAN LAA sites today, but it expects to add 4,000 more in 2018 and 2019.
Further complicating matters is that microwave fixed service systems are not built to detect interference, and the fixed service links will be unable to distinguish RLAN interference from fade caused by atmospheric or other naturally occurring conditions, according to AT&T.
This isn’t the first time AT&T has raised concerns about the potential for interfering with public safety and other critical communications in the 6 GHz band. Last year, it noted (PDF) that it wasn’t the only one sounding the alarm; both the National Public Safety Telecommunications Council and the Association of Public-Safety Communications Officials International echoed its concerns about interference with essential fixed microwave links for public safety and other critical operations.