Sharing spectrum is likely to get a whole lot easier thanks to the databases that Google and others are creating that show where nearly every building and tree in populated areas is located. This leads to better propagation models that show where available spectrum is located and where it can be shared.
Google, which benefits when more people have more and better access to the internet, is a big proponent of sharing spectrum. Google and Alphabet Access have been heavily involved in the 3.5 GHz Citizens Broadband Radio Services (CBRS) band, where the FCC is overseeing a three-tiered sharing paradigm. However, sharing spectrum could be a whole lot easier in other spectrum bands, according to Andrew Clegg, spectrum engineering lead at Alphabet Access.
The concept isn’t new; Google and its associates have previously talked about how the industry should evolve after the first-generation Spectrum Access System (SAS) is certified, which is something Google is working on with the FCC and others. The FCC is currently looking at how to manage spectrum in other bands, including 3.7-4.2 GHz and what’s being called the 6 GHz band.
In CBRS, the sharing with incumbents is primarily with the military ship-borne, high-powered radar, and they go out of their way to make sure no one knows where they are—that’s classified information, after all. CBRS spectrum administrators had to develop sensing technology to “sense” where they are.
But in the 3.7-4.2 GHz band, for example, the fixed satellite services (FSS) incumbents are relatively static in comparison; they’re not constantly moving around. In fact, once the FCC’s database on this fixed satellite dish equipment gets cleaned up, it would be comparatively easy to keep track of users in the band and thereby develop a centralized authorization mechanism to allow for sharing. A full-blown SAS wouldn’t even be required, and such a system could be set up far quicker than what’s being done at 3.5 GHz in the U.S.
Propagation models are getting more sophisticated all the time. Access and others have done their own propagation modeling that takes into account the amount of clutter, like foliage and buildings, that can cause signal degradation. With databases being developed by Google and others that show where nearly every building or tree is located in populated areas, "we can build sophisticated propagation models and get a more accurate picture to where spectrum is and where it can be shared,” Clegg told FierceWirelessTech.
Google and Alphabet Access are advocating that the FCC clean up the existing database of C-band FSS sites, then identify opportunities to share the C-band with point-to-point and point-to-multipoint broadband access for fixed broadband access (FBA) systems. Such systems have the potential to provide high-speed last-mile broadband to a neighborhood or rural area fairly quickly.
Given the relatively large number of incumbent receive-only earth stations, mobile use of the 3.7-4.2 GHz band is currently more challenging than fixed use, and getting the band ready for mobile communications will take considerably longer, according to Google and others.
“If you want to provide point-to-multipoint services, satellites could stay in the band but if you want to open it to mobile, you most likely would have to clear the satellite interests out of the band” because trying to coordinate the interference when you don’t know exactly where all your transmitters are would be very, very difficult, Clegg said. “We’ve looked at it and we don’t think you can provide [mobile] service in the band” without clearing out the satellite interests.
“We’re not against mobile in the band,” he added, but the faster way to market is with fixed wireless. And because of the amount of spectrum in the band, fixed wireless use today does not preclude mobile use as soon as satellite interests can be relocated.
“We’re not trying to take spectrum away from those who are using it,” he said. “We’re just wondering if there’s a way that we could share the spectrum” and deploy unlicensed devices without causing interference with the incumbents.
Google acknowledges that it benefits when more people are using the internet. “We’re always happy to see more ways and easier ways for people to access the internet, so that’s why we’re interested in expanding broadband access opportunities,” particularly for unlicensed, he said.