Spectrum Sharing Not Seen as Capacity Crunch Panacea

Dynamic spectrum sharing is a slow, expensive process, and though it has a role to play in meeting growing needs for mobile spectrum, it's not the silver bullet, Peter Rysavy, president of wireless tech consultancy Rysavy Research, said Wednesday in a Georgetown University Center for Business and Public Policy presentation. Beyond more spectrum, the U.S. also needs denser networks and better antenna technology to increase capacity, he said.

Complex spectrum sharing also means lower economies of scale due to the difficulty in rolling it out elsewhere, Rysavy said, pointing to the citizens broadband radio service sharing regime as the most complex sharing system in the world. CBRS took eight years between the FCC's NPRM and its license auction, and NTIA has indicated spectrum sharing regimes can take a decade to set up, Rysavy said. Licensing on an exclusive use basis can get spectrum to market much faster, even if one adds in the couple of years it might take for incumbents to relocate themselves, he said. "We need to be realistic about what can be achieved in what kind of timeframe," he said.

Simple sharing, such as AWS-3 sharing at 1.7 and 2.1 GHz, is coordinated with federal users on a permanent basis by geography, protecting federal satellite uplink stations, Rysavy said. That relative simplicity allowed for rapid deployment of the spectrum for cellular users. Conversely, complex sharing, such as via LTE Licensed Assistance Access and 5G New Radio Unlicensed for sharing cellular and unlicensed WiFi spectrum required years of engineering work. "Achieving that was an engineering marvel," he said.

The C-band auction results, with that spectrum licensed for exclusive use, had far higher auction returns than CBRS, pointing to how any operator wanting nationwide, widespread coverage with consistent service is going to want a reliable foundation of interference-free spectrum, Rysavy said.

Beyond the upcoming 2.5 GHz auction, the pipeline of future spectrum to meet mobile needs "is going to be challenging," Rysavy said. Below 2.5 GHz, "just slivers" are available, he said. While much of the world is looking at 4.8 GHz, there's no momentum for that in the U.S., he said. And different entities have claims on 12 GHz, he said. While there's ample unencumbered spectrum above 95 GHz, "the bad news is we don't know how to use that yet," he said. He said it's unclear if the spectrum sharing regime used with CBRS could be replicated with other spectrum bands, as it's aimed at sharing with specific radar systems.

While better antenna tech can increase capacity in denser networks, "we are really reaching the limits of physics" regarding tech efficiency, Rysavy said. Better receiver standards could help capacity issues a bit, he said. He said by the decade's end, there likely will be more than a million small cells around the U.S. vs. 400,000 macro sites today due to network densification.