If the world were a Utopia, all spectrum would be available under a sharing scheme so that none of it ever had to lay fallow and wasted. (And we’d all be working to solve global warming.) Sigh.
But at least in terms of spectrum sharing, implementations are gaining more steam. It’s working so well for the Citizens Broadband Radio Service (CBRS) band in the United States that people are already thinking about it for other uses.
Speaking at the recent 6G Symposium, Google Spectrum Engineering Lead Andrew Clegg said that since the initial commercial deployment of CBRS spectrum began in January, and during Covid no less, there have been 100,000 CBRS access points already deployed. This 100,000-mark encompasses the entire CBRS ecosystem, not just Google’s customers.
Federated Wireless CEO Iyad Tarazi told FierceWireless that 4,000 to 5,000 Citizens Broadband Radio Service Devices (CBSDs) are currently being added per week.
Clegg also said, “We have not had a single reported case of interference to the incumbents. We’re probably over-protecting.” He said that the SAS administrators for CBRS took an exceedingly conservative view for propagation. But Google has Google Maps, which is great at terrain data. “We want to use incredibly detailed accurate data for modern-day propagation models, so we’re not leaving many 10s of dB on the table and overprotecting,” said Clegg.
Monisha Ghosh, chief technology officer at the FCC, also speaking at the 6G Symposium said, “I think propagation models are important, but we should also take into account, as these systems roll out, we’re going to get a lot more measurement, and that will be fed back.” She said spectrum sharing in the CBRS band is just one unique use case. “Not all spectrum for sharing will have that kind of incumbent and may not need that kind of protection,” said Ghosh.
Spectrum sharing for other bands
Tarazi said there are a few other areas where spectrum sharing is now being seriously considered.
The first is the 100 MHz of spectrum in the 3.45-3.55 GHz. The Federal Communications Commission (FCC) is currently accepting comments related to using this spectrum for fixed and mobile wireless services.
Tarazi said the spectrum, if it becomes available for auction, “will look like CBRS or a variation of CBRS, potentially with higher power.” The FCC has asked for input on approaches that would incorporate aspects used for the shared CBRS 3.5 GHz band that sits adjacent. Because the 100 MHz from 3.45-3.55 GHz currently houses federal military users, Tarazi said it will “most likely need enhancements to Environmental Sensing Capabilities (ESC) networks.” ESCs include sensors along the coasts of the United States to ensure the Navy and other Defense Department agencies have first access to the spectrum, if needed.
The second area where spectrum sharing is likely to be used is in the 6 GHz band. In October the FCC decided to open up 1,200 megahertz of the band to new unlicensed users.
“A portion — about 850 MHz — is going to be shared between Wi-Fi and standalone 5G,” said Tarazi. While the CBRS band uses a spectrum access system (SAS) to coordinate usage on a dynamic basis, the 6 GHz band will probably use something similar.
Federated Wireless has built a prototype Automatic Frequency Controller (AFC) and shared it with the FCC for its review. The AFC would be used to protect incumbents while allowing for new users in the spectrum.
Tarazi likened the AFC to “a light version of the SAS.” He said, “The way to think about 6 GHz today is it has private lines. They were licensed point-to-point. Some of them are public safety private lines, or for first responders. Carriers also use it for backhaul to cell sites. That’s about 30% of the band. 70% of the band is open.”
He said Federated’s AFC takes into account where these private lines are as well as the propagation characteristics of the spectrum. Its AFC uses algorithms in the cloud, similar to its SAS, to dynamically manage spectrum for low-power standalone 5G or Wi-Fi 6.
Other spectrum sharing prospects
Finally, there are a couple of other areas where spectrum sharing may be used in the future.
A wide array of parties are interested in the 12 GHz band, including SpaceX, AT&T, Dish and Michael Dell. But it’s too soon to tell how this will play out.
And finally, the Department of Defense issued a request for information about spectrum sharing in bands that it owns between 3.1-3.45 GHz.
In terms of the DOD's interest in spectrum sharing, New Street Research analysts write that the Pentagon's arguments for greater spectrum sharing capability "will not go away with a new Administration....Rather, it is something of an opening argument that the Pentagon will make to the incoming Administration to justify its spectrum holdings."