The Federal Communications Commission (FCC) should only allow unlicensed operations in the 6 GHz spectrum band if the Commission adopts more stringent interference protections for co-channel and adjacent channel microwave systems, said a cross-section of public safety and critical infrastructure industries (CII).
In a Nov. 8 letter to FCC Chairman Ajit Pai, the broad coalition of organizations stated that any opening of the band must include proven technology to mitigate the risk of interference by prior coordination of unlicensed operations to the communications of the incumbent license holders.
The associations and utilities that sent the letter have joined together in opposition to the FCC’s Notice of Proposed Rulemaking regarding unlicensed use of the 6 GHz band. The associations and utilities that are already in the 6 GHz band, use it for point-to-point mission-critical communications throughout the nation.
The American Public Power Association is one of 11 associations that signed on to the letter, along with more than 55 individual electric utilities (investor-owned, public power and cooperatives).
In particular, the associations and utilities are concerned that the proposed mitigation scheme for protecting public safety and CII users from interference, the Automated Frequency Coordination (AFC) system, is theoretical in nature and has not been tested or proven to work.
“Moreover, the Commission’s current proposal does not contemplate a mechanism for ensuring that unlicensed users take responsibility for the cost impact of the interference resulting from unlicensed devices operating in the 6 GHz band,” the letter went on to say.
To mitigate the potential for interference to licensed microwave systems in the 6 GHz band, improvements are needed to the proposed AFC system, the associations and utilities told Pai.
“Given the significant risk that allowing unlicensed operations in the 6 GHz band could have on mission-critical communications networks, at the very least, the Commission should consider working with one or more federal laboratories to ensure that the untested interference mitigation measures proposed in the rulemaking will work before unlicensed operations are allowed in the 6 GHz band,” the letter said.
The 6 GHz band is heavily used by public safety providers, variety of CII licensees
The associations and utilities also pointed out that the 6 GHz band is uniquely suited for and heavily used by public safety providers and a variety of CII licensees for private point-to-point microwave systems.
“After being forced out of the 2 GHz band in the 1990s, CII have made very significant investments in the 6 GHz band because it is resilient to rain fading and has other characteristics that make it indispensable for CII communications. Thus, there are approximately 97,000 microwave links in the 6 GHz band, the vast majority of which are licensed by public safety or CII entities.”
Given the critical nature of the communications carried on the 6 GHz band, the public safety and CII networks operating in this band are built to extremely high standards of reliability – 99.999 percent or 99.9999 percent availability, the letter noted.
“These networks must also transmit with extremely low levels of latency – 20 milliseconds or less of roundtrip delay from one point to another – over long distances,” the groups and utilities told Pai.
Any interference from unlicensed operations would have a widespread negative impact to essential services, including emergency response and recovery, electricity, heat, water and transportation, they said.
In the area of utilities, the associations and utilities noted that electric, gas, and water utilities operate thousands of microwave links to support voice and data communications with personnel and critical assets such as substations and tele-protection systems on the grid.
“Given that grid operators must match the supply of electricity with demand for electricity instantaneously, these wireless communications must occur at a high rate of speed over long distances. Microwave links backhaul voice communications across utility service territories, including with personnel during emergency response to restore power in the aftermath of an outage,” the letter said. “Some of these microwave systems are shared with public safety, further underscoring their criticality and the need to prevent interference to these communications.”
There will likely be millions of unlicensed devices seeking access to the 6 GHz band, which will make protecting public safety and CII networks from interference extremely difficult, if not impossible, the trade groups and utilities said. “Therefore, it is also important that the Commission adopt minimum standards for updating AFC systems and clarify that unlicensed operators or AFC system operators are legally liable for the consequences of interference to licensed microwave systems in the band.”
Such an approach is necessary because CII have few, if any, options for relocating these systems should the Commission proceed as planned with this proposal.
“There is no currently available spectrum for relocation out of the 6 GHz band that provides the same capabilities, and while some of the entities we represent may consider using fiber, for many of our signatories below, deploying fiber across vast geographic territories is not economically or physically feasible. There are, on the other hand, numerous reasonable alternatives for unlicensed operations to use other bands.
Similar concerns for interference have been raised in letters to the FCC by the Department of Energy’s Assistant Secretary Bruce Walker and most recently by a bipartisan coalition of U.S. Senators led by Senators Jim Risch (R-ID) and Mazie Hirono (D-HI).
