Following up on White House and Department of Defense efforts to open up another 100 megahertz of midband spectrum for mobile networks, the Federal Communications Commission is set to vote later this month on plans for 3.45-3.55 GHz.
Chairman Ajit Pai announced yesterday that he is circulating a draft item that will be up for vote at the FCC’s next meeting on September 30. The commission will vote on a notice of proposed rulemaking (NPRM) to change the rules for 3.44-3.55 to allow for commercial use and coordination between federal and non-federal users in the band, as well as removing secondary, non-federal allocations from 3.3-3.55 GHz, which the Commission had already proposed doing last year.
“We are moving forward quickly, in coordination with the Executive Branch, to ensure that this mid-band spectrum is available for commercial 5G deployment,” said Pai in a statement, adding, “With this 3.45 GHz band proposal, the upcoming C-band auction of 280 megahertz of spectrum, and the recently completed auction for Priority Access Licenses in the 3.5 GHz band, the Commission is on track to make a wide swath of 530 megahertz of continuous mid-band spectrum available for 5G.
The White House and DoD announced last month that they intended to open up the 100 megahertz of spectrum, which is used by various defense radar systems. However, service rules for the band need to be set by the FCC, which plans to release documents today on the new proposed operations. A DoD spokesman has said that the rules are expected to be “to be similar to AWS-3, where for the most part the spectrum will be available for commercial use without limits, while simultaneously minimizing impact to DoD operations.” The AWS-3 service rules establish protection zones for incumbent operations, and commercial networks have to successfully coordinate with those incumbents to avoid interference before they can operate within the zones.
The Trump administration says that an auction of 3.45-3.55 GHz could be held as soon as December 2021, with the spectrum in use by 2022.
The National Telecommunications and Information Administration recently reported to Congress on the feasibility of sharing in the band, saying that the section of that spectrum between 3.45-3.55 GHz was identified as having “the highest probability of being able to accommodate sharing with commercial wireless services in a relatively short timeframe.”
The band, according to NTIA’s report, is “critical” to DoD and Department of Homeland Security radar operations, with DHS operating fixed and transportable radars in the band and DoD operating high-powered defense radar systems that include fixed, mobile, shipborne, and airborne platforms for air defense, missile and gunfire control, bomb scoring, battlefield weapon locations, air traffic control, and range safety. In terms of geographic area, federal operations span the entire United States and its territories, with some airborne systems operating nationwide, more than 100 locations for ground-based radars and shipborne radars that operate in more than 20 ports as well as along the U.S. coasts.
The DoD has already conducted a related 3450-3550 MHz Technical Study considering all federal systems in the band, potential aggregate interference to those systems under two different hypothetical commercial deployments and three sets of power levels for each, including “both the relatively low-power operation currently permitted for commercial operations in the adjacent band above 3550 MHz and the higher power levels that industry representatives have indicated are optimal.” While commercial systems at 3.45-3.55 GHz would generate interference with the existing ones, the study found, it “nonetheless concludes that, with a transition of nationwide aeronautical systems to alternative frequencies, proper interference mitigation mechanisms, and further study, spectrum sharing may be technically feasible for all or portions of the 3450-3550 MHz sub-band, including at all the power levels analyzed.”
The 2010 ten-year plan that highlighted this spectrum as a potential sharing candidate also jump-started the development that led to the commercialization of the three-tiered sharing framework for CBRS. So why not take the same approach that has been realized with CBRS? The NTIA report says that while the work done for CBRS “is directly applicable to the establishment of sharing between commercial wireless and shipborne radars in this band, it is less relevant to the development of appropriate systems to protect the other – ground-based and airborne – systems in the band. This is partly because industry-managed monitoring stations outside military installations are inherently problematic from an operational security perspective and many more would be required due to the large number of ground-based radar sites, and partly because there are unique technical challenges to monitoring airborne operations.” NTIA’s report had floated the idea of a government-operated Spectrum Access System (SAS)-type approach, in lieu of the commercial SASes that manage the CBRS band.