CBRS’ continued evolution likely to set the roadmap for sharing in other bands
The Citizens Broadband Radio Service’s three-tiered spectrum-sharing framework has essentially set the current standard for an automated approach to sharing between the federal government and the private sector. However, the system isn’t perfect and could be more dynamic. But CBRS’s sharing framework is evolving, much as CBRS spectrum assignments themselves can evolve.
And after more than four years of commercial use of the spectrum, both federal and private sector users have a better grasp of the real-world operations of the band, and how to effectively protect naval radar incumbents while expanding the number of users who don’t ever have to be bumped out of the band to make way for those incumbents.
By the end of 2023, there were about 370,000 active CBRS devices, or CBSDs, transmitting across the United States, and more than 1,000 entities operating CBRS networks. Meanwhile, not a single instance of harmful interference with naval systems has been reported, according to Sarah Morris, principal deputy assistant secretary and deputy administrator (acting) for the National Telecommunication and Information Administration (NTIA), speaking at an event in Washington, D.C. on Tuesday morning. CBRS has proved, Morris added, that dynamic spectrum sharing can work at scale. But the related tools can be sharpened, she continued, to provide more “unfettered use” under which CBRS users will not be preempted, while still protecting critical government systems.
Newly proposed changes to the aggregated interference model on which CBRS sharing is based, are expected to enable CBRS Spectrum Access System administrators to provide “uninterrupted access” to approximately 72 million more people than they do now, in an iteration of the system being dubbed “CBRS 2.0”. According to Andrew Clegg, spectrum engineering lead for SAS administrator Google, SAS administrators are already conducting testing and the changes for CBRS 2.0 are expected to filter through the related regulatory approval processes and be implemented before the end of this summer.
Keri Pasquini-Thompson, deputy director of spectrum policy and innovation for the Department of Defense CIO, outlined a number of changes that government and private users have worked through that improve the CBRS systems. In Hawaii, an automated scheduling portal was created to enable access to the band before Environmental Sensing Capability sensors were available to implement the ESC locally. The ESC detects naval radar systems and provides that information to Spectrum Access System (SAS) providers in order to preempt other use of the band.
Additionally, the CBRD “heartbeat,” or how frequently that CBRS devices have to check in with the SAS to be reauthorized to operate in their assigned spectrum, was considerably lengthened. Some CBSDs went from having to check in every five minutes, to once every 24 hours, even within protected zones, depending on which part of the band they were operating in. An enormous Dynamic Protection Area (DPA) that extended nearly 300 kilometers from Nevada to the Pacific Ocean and included cities such as Los Angeles, Las Vegas and Bakersfield, was split into two: One for the air, and one for the ground, in order to reduce the CBRS preemption for users on the ground.
The CBRS 2.0 changes to the aggregate interference model reduce the Dynamic Protection Areas (DPAs) where access to the spectrum can be suspended for non-incumbents, decrease the number of grants for Citizens Broadband Radio Service Devices (CBSDs) that have to be suspended when a DPA is activated and enable more accurate propagation modeling “due to higher confidence through experience,” according to an NTIA letter to the FCC requesting the changes to the CBRS framework.
At the D.C. event, the general consensus was that the lessons learned from CBRS—and from the willingness of federal agencies to revise the system for greater commercial access—will help to shape the use of other bands, hopefully with even more flexibility.
“When I look at sharing in general, and when you look at the bands being proposed, those are different challenges, and different systems in the band,” acknowledged Elvira Pearce, deputy director, Department of the Navy Strategic Spectrum Policy SRF Policy Lead. That doesn’t necessarily mean a CBRS-like approach will work, she continued, adding, “Whatever sharing framework we come up with, we need to recognize that it needs to be more flexible.” She emphasized that all the stakeholders were “trying to come together to find a way to share—and I think as we move forward with other bands, we’re going to come to that same conclusion, that that’s the end state: How do we get to ‘yes’?”
Jennifer McCarthy, VP of legal advocacy for SAS administrator Federated Wireless, pointed out that when CBRS was first implemented, the Department of Defense was upfront that it was being very conservative in protection of its systems. “That was a reasonable position to take on a brand new thing. But having the commitment to take another look at it, and looking for additional opportunities for improvement, was fantastic,” McCarthy said. “And I think we just need to remind ourselves that we should do that all the time. This should be a regular event, where we look at what can be continually improved, and how it can be adapted and extended to other bands and other situations. We have learned an awful lot here with CBRS, and the work that we have collectively done should not be overlooked.”
