The U.S. military might have to share its radar frequencies with mobile broadband providers under a plan the Federal Communications Commission continued to flesh out this week under the catchy name Citizens Broadband Radio Service.
CBRS isn't exactly a broadband version of Citizens Band radio — which still exists, at astonishingly low frequencies around 27MHz — but the FCC's description of what it might be used for suggests a broad range of options. They include licensed carrier cells, fixed wireless broadband, advanced home networking and other uses, the agency said. It's seeking public comment on the proposals.
The proposed rules could allow sharing a wide band of spectrum spanning 3550MHz to 3700MHz. Parts of that spectrum are home to high-powered military radar, especially within 200 miles of U.S. coastlines, which is also home to a majority of the country's population. To prevent interference, the FCC calls for using a dynamic database to keep track of where and when the frequencies can be used. Network equipment can tap into such databases to find out whether a certain frequency is being used in a given area.
Though the concept of spectrum sharing with a database is similar to the so-called "white spaces" that are open to unlicensed use around TV channels, the CBRS band would be a bit different. It would have three classes of users. Federal and non-federal incumbent users would be first, protected from interference from the new services. Next would be "targeted priority access," including licensees offering mobile broadband.
Finally, "general authorized access" users would be permitted "in a reserved amount of spectrum and on an opportunistic basis," the agency said. That could include both consumer and business uses.
Mobile operators and some lawmakers have opposed spectrum sharing, saying exclusive, commercial spectrum licenses better serve consumers. But the President's Council of Advisors on Science and Technology recommended in 2012 that the government find ways to share as much as 1.5GHz of spectrum. It identified the 3.5GHz band as the best target for early sharing.
The 3.5GHz band is higher than the frequencies typically used for mobile broadband, making it better suited to so-called small cells, miniature base stations designed to serve tightly packed urban users over short distances. Technology advances in small cells and in spectrum-sharing systems will help to make CBRS feasible, the FCC said.
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