AT&T Joins Public Safety, CII in Opposing Unlicensed Operation at 6 GHz
Tuesday, February 19, 2019 | Comments
AT&T joined public-safety groups, several coalitions of critical infrastructure industries (CII) organizations and numerous 6 GHz incumbent licensees opposing unlicensed use of the band. The comments were in response to a 2018 FCC notice of proposed rulemaking (NPRM) that suggested making up to 1,200 megahertz of spectrum available for use by unlicensed devices in the 6 GHz band (5.925 – 7.125 GHz).

AT&T said that in addition to licensed operations for public safety, utilities and wireless backhaul, carriers such as AT&T rely on point-to-point microwave to interconnect cell cites, and 6 GHz use will only increase with 5G technology network densification.

“Given the present state of the record, AT&T remains highly doubtful that unlicensed uses could, under those or any circumstances, harmlessly coexist with the critical licensed uses in the 6 GHz band,” the carrier’s comments said. “These essential services operate, by necessity, with a miniscule margin for error and are therefore highly vulnerable to harmful interference. Those seeking to introduce potentially disruptive, unlicensed uses into the 6 GHz band (RLAN advocates) should therefore bear the burden of demonstrating, by clear and convincing evidence, that the proposed uses would cause no harmful interference.”

The National Public Safety Telecommunications Council (NPSTC) said based on the history of interference in the 5 GHz band and other spectrum, it questions whether unlicensed sharing in the 6 GHz band is sound spectrum policy. The council noted the 6 GHz band is the only band available to support links of long distances — those greater than 30 miles.

“However, members of the commission do appear to have already decided to allow such sharing, even before any comments to the NPRM are received,” NPSTC said in its comments.

The council offered technical changes to the proposed 6 GHz unlicensed rules to help avoid interference to incumbents, which specify 99.999 percent or sometimes 99.9999 percent reliability levels. NPSTC said spectrum sharing should not erode fade margins, should not be allowed on frequencies designated for temporary links and must be organized through a centralized automated frequency coordination (AFC) spectrum access system. The council also recommended extensive trials and testing of the AFC.

The Association of Public-Safety Communications Officials (APCO) International expressed concern that the proposed unlicensed use in the 6 GHz band will cause harmful interference to public-safety operations. “Spectrum bands housing public-safety operations are not the appropriate arena to deploy new, unproven spectrum sharing and frequency coordination methods,” APCO’s comments said. “Should the commission proceed, it must substantially revise its proposal and ensure effective mechanisms are in place to mitigate potential interference and rapidly resolve any interference should it occur.”

APCO offered detailed input on the FCC’s proposed rules for allowing unlicensed devices in the band from the technical rules to the details of protecting incumbents from interference.

In joint comments with the American Petroleum Institute (API), the American Public Power Association (APPA), the American Water Works Association (AWWA), the Edison Electric Institute (EEI), and the National Rural Electric Cooperative Association (NRECA), the Utilities Technology Council (UTC) said it is against the FCC’s proposal to open up the heavily used 6 GHz band to unlicensed use.

“Any benefit from the expansion of unlicensed operations in the 6 GHz band is outweighed by risking interference to mission-critical communications and therefore is not in the public interest,” the six groups said in their comments.

The groups specifically took issue with the AFC proposal, saying it is a purely conceptual approach that has not been proven to perform as promised. “Given that similar failures will occur with the proposed AFC approach, if the FCC goes forward with expanded unlicensed operations in the 6 GHz band, there must be a plan to address interference when the AFC system fails,” UTC said in the joint filing. “Moreover, it is unclear whether AFC will be centralized and whether the FCC will provide the enforcement mechanisms needed to enable incumbent licensees to remedy interference that is caused by unlicensed operations.”

The comments included a white paper titled “Spectrum and Utility Communications Networks: How Interference Threatens Reliability.”

The Critical Infrastructure Coalition — comprised of 13 utilities, energy and oil companies — hold more than 600 6 GHz licenses. The coalition said unlicensed operations in the band threaten the integrity of the 6 GHz communications systems used by the licensees.

“If the commission does not adequately ensure that existing fixed point-to-point 6 GHz networks operated by coalition members receive sufficient interference protection, the resulting impact of new unlicensed users could be catastrophic,” the Critical Infrastructure Coalition comments said.

The American Association of Railroad (AAR) said because of incumbent licensees’ need for reliable service in these frequency bands, the association opposes introducing new unlicensed services in the 6 GHz band. “Operation by unlicensed devices could interfere with incumbents’ mission-critical operations,” AAR said, while offering a list of safeguards the FCC should implement if it moves forward with unlicensed use of the band.

Motorola Solutions said it generally supports the FCC’s spectrum sharing approach but to effectively share the spectrum, the FCC should employ cloud-based AFC mechanisms. “This approach will best allow critical updates to protection information (such as new or modified incumbent operations, interference protection levels, shut down of interfering devices, etc.) to be made in a timely and effective manner,” Motorola’s comments said.

For its part, Verizon said as long as valuable incumbent users are protected, unlicensed use in 6 GHz spectrum holds substantial promise to develop new services and enhance existing ones. “The key to promoting unlicensed use in the 6 GHz band is a sharing model that protects incumbents through a cloud-based, IP-connected AFC manager,” Verizon’s comments said. “Unlike traditional unlicensed approaches that involve free-standing unmanaged devices, the AFC should use a ‘closed loop’ network framework that positively controls unlicensed radio access to the band and thereby protects incumbent operations.”

The comments can be accessed on the FCC website.

Reply comments are due March 18.

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