- CBRS advocates are urging the FCC to reject proposals for higher power in the 3.5 GHz band
- One study shows roughly 75% of U.S. private 5G networks rely on CBRS
- Another study shows the disruptive impact a proposal to raise maximum power levels would have on existing CBRS users
The Citizens Broadband Radio Service (CBRS) community has a message for anyone pushing for higher CBRS power levels: back off.
CBRS proponents this week held a webinar hosted by New America where they highlighted two studies – one showing how the private wireless CBRS network market is growing and another describing the enormous disruption that would result if higher power levels were introduced.
For the past several years, wireless carriers have been pushing for higher power base stations in the 3.55-3.7 GHz CBRS band, similar to what they use in their fully licensed bands on either side of the band. Otherwise, they say, it’s not much use to them. The issue is part of a Notice of Proposed Rulemaking (NPRM) pending at the Federal Communications Commission (FCC).
The CBRS band is a combination of unlicensed, licensed and shared uses, and it’s what has enabled corporations like John Deere, BMW and Dow Chemical to deploy their own private networks and keep U.S. manufacturing humming on American shores, said John Puskar, CEO of the America Made 5G coalition. In addition, hundreds of wireless ISPs use CBRS to deliver internet to homes and businesses in rural areas.
“The great thing about CBRS is it really democratized access and allowed more people to be able to have access to these types of networks, which before wasn't possible,” he said.
Public cellular has its place, but CBRS is how American factories are connecting, and it’s just getting started, Puskar said. Development of the CBRS ecosystem got underway about 10 years ago, but it’s been only five or six years since the first equipment was authorized by the FCC.
Today, the CBRS ecosystem is home to nearly 1,400 FCC-approved devices, and more than 430,000 CBRS base stations are deployed in the field.
“We have more [private networks] than any other country in the world,” and 75% are running on CBRS, a number expected to increase to 85% by 2032, Puskar said, citing an Analysys Mason study.
The CBRS community has good reasons to be concerned about the status of their spectrum. AT&T in 2024 famously proposed relocating the entire CBRS band to the lower 3 GHz band, which is occupied by the military. But last year, Congress basically took the lower 3 GHz out of play at the request of the military, said New America/Wireless Future Director Michael Calabrese.
Still, the CBRS band remains at risk of proposals to move it elsewhere because in the same legislation last year, Congress directed the auction of 800 megahertz of spectrum for commercial wireless use over the course of nine years. It’s not definitively decided where all of that spectrum will come from.
CBRS power levels
Right now, the comment period remains open at the FCC on proposals to increase CBRS power levels, and Puskar said that’s the issue that appears to be the most imminent.
Currently, two categories of CBRS base stations are allowed: Category A devices that operate up to 1 watt; and Category B devices that go up to 50 watts. Proposals have called for two additional categories: Category C, with a limit of 1,585 watts, and Category D, with a whopping 15,849 watts per channel.
“For those of you who are Spinal Tap fans, it’s sort of like saying your amplifier goes up to 11,” Valo Analytica CTO Andrew Clegg said. “It really is off the charts almost.”
Clegg, along with Mark Gibson, spectrum policy director at CommScope, did a study for Spectrum for the Future, a cable-led CBRS organization, to see what would happen to existing CBRS operations if higher power base stations were allowed in the band.
Both Clegg, formerly with Google, and Gibson are experienced spectrum engineers who were involved in building CBRS Spectrum Access Systems (SAS), which act as traffic controllers, and they used that background for their study.
“We also helped develop the standards that Spectrum Access Systems run on, so we know very well how the SAS is supposed to work and how it’s doing its calculations,” Clegg said.
They created their own software-based SAS model and worked with KeyBridge Technologies to deploy high-powered CBRS base stations to measure their impact in the real world.
The upshot: They found that if fewer than 2% of CBRS base stations were converted to high power, there would be a massive loss of data throughput across the CBRS ecosystem and it would slow network operation to a crawl.
Miami airport uses CBRS
In addition to their technical study, Clegg and Gibson looked at what would happen to actual CBRS users, including Miami International Airport (MIA) and Ohio-based wireless ISP Amplex Internet, if higher power CBRS devices operated near their networks.
MIA uses its CBRS network for video surveillance, baggage handling, elevators, smart restrooms and more. If you were to put a single Category D base station in the Miami metro area, it could take as much as one-third of the airport’s network off the air, Clegg said.
“A loss of a third of their network, they considered, would be catastrophic, and so this would have an immediate negative impact to the Miami International Airport,” he added.
Amplex gets static
Amplex Internet delivers broadband to homes and businesses in northern Ohio, where Amplex CBRS base stations sit right across the border from Canada.
The macro cellular service providers in Canada use the same 3.5 GHz frequency band as CBRS in the U.S. and operate at a higher power. That means Amplex’s north-facing base stations that are immediately south of the Canadian border consistently suffer outages. Consequently, Amplex customers lose their internet service repeatedly throughout the day and night, sometimes for one or more hours at a time.
Interference from the high-power Canadian base stations occurs at distances of 220 kilometers away, and “the power levels that the Canadian stations are operating at are basically identical to those that are being proposed by Category C and Category D,” Clegg said.
Put another way, when a proposed higher power Category C or D device is introduced in the CBRS band, it’s sort of like walking into a crowded restaurant with a megaphone, he said.
“Imagine all these people at tables for two or whatever having nice, quiet conversations over dinner, but then somebody walks in with a megaphone and starts shouting through the megaphone. You can no longer have all of those little conversations. Everybody has to listen to the person with the megaphone, and that's the only person who gets a signal out and across,” Clegg said. “That's what would happen if you allow higher power in the CBRS band.”