Co-channel sharing of satellite C Band spectrum is feasible with far smaller geographic protection areas than are currently in place, according to a new study — and trimming down the exclusion zones around satellite earth stations and enabling spectrum sharing could open up high-speed wireless broadband service for 80 million Americans, the study’s authors concluded.
The results of the study, which was backed by Google, Microsoft and the Wireless Internet Service Providers Association, were presented at an event in Washington, D.C. yesterday. Claude Aiken, president of WISPA, said that the 500 megahertz of C Band spectrum is “currently quite underutilized as a result of overprotective policy” and that the study shows that sharing is feasible. Aiken said that if the C Band spectrum were repacked and shared with satellite operations, it would result in multiple operators capable of providing gigabit or near-gigabit speeds to serve rural areas “nearly overnight.”
The C Band is currently the subject of a Federal Communications Commission proposed rulemaking in which the FCC is asking for comment on how the spectrum might be more efficiently used and either cleared or shared for terrestrial wireless services. The C Band Alliance, which is made up of major satellite players, has proposed freeing up 200 megahertz of the 500 megahertz for flexible use and conducting a private auction of that spectrum. Opponents to that plan argue that satellite players could make more of the spectrum available, and that the process should be run by the Federal Communications Commission as a public auction.
The lead author on the study, Professor Jeff Reed, founded the wireless research group at Virginia Tech and is a co-founder of Federated Wireless. Andy Clegg of Google noted during his introduction of Reed that the spectrum sharing in the Citizens Broadband Radio Service spectrum at 3.5 GHz — which Federated’s solutions enable — also involves coordination with fixed satellite service earth stations, as the FSS stations are one of the incumbent types in the band.
Clegg added that the FSS stations are the “poster child” for “super-sized”, overprotective geographic zones in which other uses of the spectrum are not permitted due to concerns about interference. Those zones, he said, have a radius of 150 kilometers or about 70,000 square miles around each station — which he said means that for every one FSS station, the protection zone is larger than 10 of the 50 U.S. states, under rules which were put in place decades ago and have not been revisited.
Reed said that his work concluded on a statistical basis that a radius of 10 km is sufficient to protect most of the FSS stations from co-channel interference.
“I would say that that’s probably a conservative number,” he added. In practice, he went on, specific siting of point-to-multi-point systems would need to ensure that placement did not result in interference: the terrestrial base stations could not point toward the FSS, for example. But “statistically speaking, about 10 km is a good number,” Reed said.
The study was based on a number of data sources and calculations, including FCC data for 18,000 FSS earth stations, 3GPP non-line-of-sight propagation models and common heights for base stations and customer premise equipment; Reed said that the study examined the county level for exclusion zones and built from there on estimates of how many people could be served if the spectrum were able to be shared by wireless broadband services.
Meanwhile, earlier this week, two trade associations (including the Competitive Carriers Association) and Charter Communications filed a proposal with the FCC on C Band that they said would free up even more spectrum than the C Band Alliance has proposed, while addressing some of the common objections that both proponents and opponents of the CBA’s plan have raised.
CCA, cable trade group ACA Connects and Charter say their proposal would “free up a large amount of spectrum—at least 370 megahertz—for 5G services, while also concurrently making all existing users of the spectrum whole; provide those users with incentives to forego their rights to the C-band frequencies; endow the entire nation, including unserved rural areas, with fiber connectivity; reserve for the American public a significant portion of the proceeds from the refarming of the spectrum; and ensure the disinfectant of sunlight—a public process free of backroom deals.”
That proposal was laid out in greater detail in the filing, which proposed a two-step refarming process, covering clearing costs, and an FCC-run auction (either a traditional auction or an incentive auction). The FCC should also gather more technical information on engineering matters including interference, the filing said, because the “UE emission mask requirements proposed by the CBA to protect adjacent satellite services from [out of band emissions]are neither realistic nor reasonable, and could cripple deployment of 5G services in the band,” and “CBA’s proposed … requirements would necessitate an exclusion zone of several kilometers around all … registered earth stations.”
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