The U.S. wireless industry would like to use the lower 3 GHz band, but it’s currently occupied by the military. The DoD says sharing between federal and commercial systems is not feasible unless certain conditions are met. Sharing between federal radar and mobile systems presents unique challenges, especially for airborne operations.

The DoD acknowledges the potential of freeing up some of the spectrum for 5G use, emphasizing that in order to make the lower 3 GHz band available for commercial use a “coordination framework must facilitate spectrum sharing in the time, frequency, and geography domains,” notes Broadband Breakfast.  

5G already coexists with U.S. military systems in the lower 3 GHz band in more than 30 countries, said Umair Javed, CTIA senior vice president-spectrum. However, the future of the lower 3 GHz band in the U.S. is unsettled following DoD’s public release last week of a redacted version of its Emerging Mid-Band Radar Spectrum Sharing Feasibility Assessment [1.].

Note 1. Emerging Mid-Band Radar Spectrum Sharing Feasibility Assessment report

This redacted DoD report examines military systems located in lower 3 GHz spectrum, with an eye on potential sharing but not on clearing as sought by CTIA and carriers.  It concludes that sharing the 3.1-3.45 GHz band between federal and commercial systems is not currently feasible “unless certain regulatory, technological, and resourcing conditions are proven and implemented.”  The report originally came out in September 2023.

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DoD Chief Information Officer John Sherman said in February the department is willing to consider clearing part of the band “perhaps for future airborne radars,” which wasn’t part of EMBRSS. The spectrum is home to the Airborne Warning and Control System (AWACS), which DOD is upgrading. Airborne radars are considered the most difficult to address in a sharing regime because they are so mobile.

The lower 3 GHz is one of a few bands allowing for military radars “with small enough antenna apertures” to be mobile, with “sufficient range capabilities to serve as medium and long-range radars,” the study says. It notes the propagation characteristics of mid-band spectrum, which also make it a top target of carriers. “A complicating factor … has been the increased packing of federal systems relocated from other bands, including those as a result of repurposing from previous auctions,” the study says.

DoD found that more than 120 different ground-based, ship-borne and airborne radars use the band. While details are redacted, the report offers basic information on how the bands are used, for everything from land-based radar for tracking threats to Coast Guard and Navy search and rescue missions to air-traffic control to tracking bird migrations with an eye toward avoiding collisions. It also discusses the Department of Homeland Security’s uses.

But EMBRSS says sharing is possible using a dynamic spectrum management system (DSMS). It cites sharing in the citizens broadband radio service band. A DSMS, which “evolves the CBRS framework … with advanced interference mitigation features” addressing the unique needs of airborne systems, “provides a feasible path forward for spectrum sharing between the Federal and commercial systems,” EMBRSS said.

Blair Levin wrote Wednesday in a note to New Street clients.:

“The report’s most significant implications for investors involve what the DOD report did not do.  It did not resolve any issues or provide a timetable for doing so. Thus, we remain far from resolving the question of where the spectrum that the wireless carriers argue they will need by 2027 will come from. While some advocate exclusive licensing of the band, and others sharing, DOD “almost certainly retains a veto power over any potential outcome,” he said.

DoD leaders, including John Sherman, the Pentagon’s top IT official, met Monday with the National Spectrum Consortium, a group of more than 350 members of academia and industry who work with the electromagnetic spectrum, to take the first steps to outline a framework to share the bandwidth with industry and to kickstart a discussion on a spectrum management program.

“No surprise. We know that spectrum will be challenging,” said Kevin Mulvihill, the Pentagon’s deputy chief information officer for command, control and communications. “But we need to work together across industry, government and academia to explore potential ways to achieve spectrum coexistence for the benefit of the entire nation while ensuring that the spectrum sharing that we choose does not negatively affect the primary mission of the Department of Defense.”

References:

https://dodcio.defense.gov/Portals/0/Documents/Library/DoD-EMBRSS-FeasabilityAssessmentRedacted.pdf

https://www.fierce-network.com/5g/dod-releases-long-awaited-report-lower-3-ghz

If the Pentagon has to share 5G spectrum, it wants some new ground rules – Breaking Defense