Denver, LA County, others oppose ‘sharing’ of 6 GHz band

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A group representing Los Angeles County, the City and County of Denver and others argue that the 6 GHz band where they operate is too important for public safety to risk being shared.

Remembering previous forced relocations to accommodate wireless carrier interests, several city and county entities are urging the FCC to keep the interests of public safety in mind as they consider rule changes to the 6 GHz band—and they have an ally in AT&T.

Several counties, along with the Government Wireless Technology & Communications Association (GWTCA), jointly filed comments saying they’re “adamantly opposed” to any “sharing” of the 6 GHz band in which their microwave links exist. The counties included Los Angeles County, California; the City and County of Denver, Colorado; the City of Kansas City, Missouri; and Ozaukee County, Wisconsin.

“The Joint Commenters have already been through two forced relocations to accommodate such carrier interests, including the 800 MHz reband and the 2 GHz relocation to create PCS spectrum,” the group said. “However, at a certain point the needs of public safety must take precedence.”

Public safety agencies know all too well the interference problems that erupted due to Nextel Communications’ operations at 800 MHz adjacent to public safety licensees and the years it took to get settled. “Interference from mobile devices is notoriously difficult to locate for mitigation,” the joint filers said. “Increasing the opportunities for mobile interference within the band is an unnecessarily high risk.”

Indeed, 800 MHz post-rebanding interference mitigation cost the City of Oakland more than a half million dollars, they noted, and Oakland is not alone in encountering such interference, post-rebanding.

In a separate filing (PDF), AT&T, which is the network provider for FirstNet, the nation’s first broadband network dedicated to public safety, said it also believes the 6 GHz microwave bands are not suitable candidates for either shared mobile use or for relocation—“these bands are densely populated and serve societally beneficial requirements that cannot technically be satisfied using other microwave bands or alternative transmission technologies.”

Of course, AT&T has its own reasons for arguing that the 6 GHz bands—specifically, 5.925-6.425 GHz and 6.425-7.125 GHz—are not good candidates for sharing or relocation. AT&T alone holds 8,138 licenses supporting backhaul for its wireless network and main telecom links for its landline network.

AT&T says 6 GHz is a rapidly deployable option for circuits where fiber optic transmission is not available, and in many cases, 6 GHz microwave can reach locations fiber cannot—or where fiber cannot reach under reasonable financial constraints, such as mountain tops.

RELATED: FCC eyes midband spectrum between 3.7 and 24 GHz

In addition, the 6 GHz Band is the last significant band allocated for commercial microwave use that is relatively unaffected by rain fade—a phenomenon that is typically viewed to begin at about 10 GHz.

“Microwave links in this band are usually engineered with ‘five nines’ of availability—uptimes that are 99.999%, or outages on the order of approximately 30 seconds per month,” the filing stated. “The added fade resulting from atmospheric weather conditions prevailing above 10 GHz would be unlikely to allow engineering of links of similar length with this class of availability.”

Plus, 6 GHz microwave is not susceptible, like fiber, to cable cuts, which makes it a uniquely important asset for critical communications on a standalone basis or as a backup to fiber—and many of these links backhaul traffic from cell sites and therefore are integral to the proper functioning of the nation’s 911 system, AT&T said.

While 6 GHz antennas are not immune to disaster, 6 GHz systems typically are also some of the fastest systems to be brought back on-line in any post-disaster restoration effort.

The counties' opinions on the 6 GHz band are just a sample of the comments the FCC is reviewing on mid-band spectrum. Comments were due Oct. 2 in the FCC’s inquiry, which primarily examines but is not limited to three specific bands: 3.7-4.2 GHz; 5.925-6.425 GHz; and 6.425-7.125 GHz. Reply comments are due Nov. 1.