The OnGo Alliance and New America’s Open Technology Institute have convinced federal regulators to relax some of the rules around Citizens Broadband Radio Service (CBRS). The organizations expect these changes to boost investment in private networks operating in the 3550-3700 MHz band, because more entities will be able to deploy in areas previously reserved for the U.S. Navy.

“If you don’t smell salt water you are probably going to be OK for indoors, low altitude [CBRS networks],” joked Preston Marshall, OnGo Alliance chairman and director of wireless policy and standards at Google.

In reality, mathematical tests rather than smell tests will determine where commercial users can deploy CBRS without fear of being kicked off the airwaves by the Navy.

Andy Clegg, OnGo Alliance director and spectrum engineering lead at Google, explained the mechanism that will free up more spectrum for commercial use.

“The totality of CBRS devices you have to include in your interference calculation is based on a certain area around the DoD operations area,” he said. “With these new changes that area is going to shrink dramatically, so the number of devices that could possibly contribute to the interference goes way down.”

Some heavily populated regions near the East, West and Gulf Coasts will now seem less risky for commercial CBRS deployments, the Google executives said. But the government still gets priority. In any part of the country, if the Department of Defense (DoD) actually uses the airwaves now or in the future, other users will have to defer.

The new rules won’t change anything about the way CBRS spectrum is allocated. Incumbent users and the government still have top priority, followed by license holders, and then others who can use the spectrum for free if it is available. This is called General Authorized Access. 

No interference

The DoD and some fixed satellite operators are the original users of the CBRS spectrum, which was opened up to new users through a rule change and auction in 2020. Since that time, there has not been a single reported use case of interference with the Navy, according to Marshall. “We were therefore probably correct in our assumption that we were overprotecting the DoD,” he said.

So Google organized a meeting with users of CBRS, including engineers from both the wireless and cable industries, as well as representatives from the National Telecommunications and Information Administration (NTIA) and the DoD. Stakeholders created new templates for the different categories of CBRS networks: indoors with antennas placed less than 6 meters above ground, indoors with antennas more than 6 meters above ground, outdoors below 6 meters, and outdoors above 6 meters. Entities looking to deploy CBRS will see the most dramatic increase in opportunity for indoor antennas less than 6 meters above ground, Marshall said.

These indoor deployments are a sweet spot for private wireless networks. CBRS vendors have positioned their equipment as a more reliable and deterministic substitute for Wi-Fi, since it gives enterprises a way to deploy their own LTE or 5G networks without necessarily paying service fees to a mobile network operator. But Marshall said some enterprises have been reluctant to invest due to fears that they could be kicked off the spectrum to protect the airwaves for the Navy.

Now Marshall and his colleagues at Google hope enterprise users will be more willing to invest in CBRS, and more able to leverage 5G standalone (5G SA) private networks.

Spectrum Access Systems

Google is one of the companies that operates a Spectrum Access System (SAS), software which calculates the likelihood of interference, blocks signals that could interfere with the Navy, and also blocks unlicensed CBRS users if they are interfering with a license holder. The other SAS operators are Federated Wireless, Key Bridge Wireless, Red Technologies, Amdocs, Sony and Nokia, which Marshall said is not fully certified yet.

Google and Federated Wireless are the two SAS vendors with the biggest market shares. Both have fully developed Environmental Sensing Capabilities (ESCs). These are what they sound like – networks of sensors that probe the environment for signals in the 3550-3700 MHz band. If the Navy is transmitting, commercial users cannot.

SAS vendors that don’t have full ESCs have to rely more heavily on interference calculations to estimate the likelihood of Navy transmissions. Now that NTIA has agreed to reduce the area at risk of naval interference, these companies could be stronger competitors to Google and Federated Wireless, Marshall predicted.

Speedy process

Marshall and Clegg said the new rules were developed quickly because the government agreed to let industry design and conduct the tests and then share results. Now that the results are in, NTIA is on board with the new framework, and will send it to the FCC for approval. The executives expect that to happen before the end of the summer.

Spectrum sharing with the government is not always easy, Marshall noted, but he said that in this instance, federal officials were ready to listen and act. “There are things Andy and I had worked out that we thought would be reasonable objectives, and what the government has offered is considerably more than anything we would’ve had the guts to ask for,” he said.

Marshall hopes NTIA’s cooperation is a good harbinger for the National Spectrum Strategy. “The government is willing to really work to make the sharing work, at least in this one case,” he said. “It doesn’t necessarily show what will happen in the future, but it certainly shows what’s possible.”

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