- CBRS deployments have grown exponentially during the last five years.
- Most CBRS network users experience reliable performance, but some private networks are recording interference from public carrier networks.
- Private network operators may see changes in CBRS radio power levels, because the Spectrum Access Systems control these.
Deployments in the 3.55 GHz - 3.7 GHz Citizens Broadband Radio Service (CBRS) spectrum band have skyrocketed since the U.S. government auctioned licenses and opened the shared band for commercial use in 2020. But now, some entities using CBRS networks find themselves in need of some elbow room, as proliferation of CBRS radios (CBSDs) in some geographies prompts concerns about interference and reduced power levels.
“The issue we are starting to see is outdoor areas where there are lots of CBSDs,” said Todd Kelly, CTO of integrator STEP CG, which works closely with Ericsson on CBRS deployments. Las Vegas in particular is one of the most crowded areas for CBRS, he added.
Between April 2021 and July 2024, the number of active CBRS devices jumped from 129,782 to 400,403, according to data from the NTIA. By May of this year, the number had risen even higher to 450,000, according to Federated Wireless.
Federated Wireless - alongside Google - is one of the top providers of Spectrum Access Systems (SAS), which use a vast network of sensors to make sure commercial CBRS radios do not interfere with the U.S. Navy, the original user of the band. These systems have been so successful that last year the U.S. government expanded the area for commercial transmissions, leaving only coastal areas with stricter limitations on commercial CBRS.
But interference with the U.S. Navy is not the only interference private CBRS network operators have to consider these days. As deployments increase, commercial CBRS radios can start to interfere with one another.
So far, instances of interference are few and far between, said Stephen Leotis, president and co-founder of CBRS private networks provider Moso Networks. He said CBRS still provides a very reliable experience for most users, but he has one private 5G customer fighting interference from a macro network. (Mobile network operators Verizon and EchoStar/Boost both purchased licenses to use CBRS spectrum, as did several cable MVNOs.)
“The interference is experienced as lower throughput, inconsistent connectivity, and poor user experience,” Leotis said via email. “CBRS is reliable, but does need RF survey/qualification/monitoring after installation.”
Hitting the power ceiling
Another issue with the proliferation of CBSDs is power limitations imposed by the SAS operators.
In addition to the licensed portion of the band, CBRS provides General Authorized Access, or GAA, which means the spectrum is free and unlicensed but the user must relinquish it to the Department of Defense or to a license holder if needed. It also means the Spectrum Access System can reduce radio power levels to accommodate these higher priority users.
“Federated and Google control these algorithms for power, bandwidth and channel allocations,” explained Leotis. “The customer has limited control over this and must understand while the radio can achieve maximum CBRS CatB power, it may not be granted this power and could be granted limited GAA bandwidth depending on the location, density, etc.”
This is becoming a bigger concern as the number of CBSDs rises, said Kelly of STEP CG. His team is currently working on a video monitoring use case that will require several non-overlapping 10 MHz channels.
“It's totally up to the SAS on whether it will grant the required channel bandwidth and power levels to achieve this use case in GAA,” Kelly said. “By watching current outdoor CBSD numbers through Federated SAS in this area and their spectrum consumptions (without knowing their heights or power level), we as well as everyone from Ericsson believe it is going to be very tight.”
Kelly said STEG CG may end up advising some customers to pivot to licensed spectrum, a costlier but more reliable solution. Leotis is also thinking about licensed spectrum, and he said Moso Networks’ next generation of radios will support C-Band as well as CBRS.
But the entire CBRS band could become licensed spectrum anyway, if AT&T and the Department of Defense can persuade the FCC to move current users down to the 3.1 GHz - 3.4 GHz band and auction off the airwaves currently used for CBRS.
For the time being, the FCC has neither a quorum of commissioners nor the authority to conduct spectrum auctions, but once these issues get sorted there’s a chance the entire CBRS operation could be forced to move.