The FCC is proposing a new "Citizens Broadband Service" (CBS) that would occupy spectrum between 3550 and 3650 MHZ. The Further Notice of Proposed Rulemaking (FNPRM) outlines rules for the new service and also requests comments on extending the proposed service up to 3700 MHz.
The proposal would rely on the FCC's Spectrum Access System (SAS) to avoid interference to incumbents currently using that portion of the spectrum and would recognize different classes of service with different protection. These proposed rules expand on the database concept originally developed for managing TV Band devices (white space devices) to avoid interference to wireless microphone and TV signals. SAS is likely to be applied other RF spectrum to allow efficient shared use of the spectrum by licensed and unlicensed users.
As stated in the FNPRM: "The 3.5 GHz Band could be an 'innovation band' where we can explore new methods of spectrum sharing and promote a diverse array of network technologies, with a focus on relatively low-powered applications. If successful, the spectrum sharing model proposed for this band could ultimately be expanded to other spectrum bands and transform the availability of a precious national resource—spectrum--from scarcity to abundance."
The FNPRM specifies three tiers of service: Incumbent Access, Priority Access (PA), and General Authorized Access (GAA). PA licenses would have to protect incumbents and GAA users would have to protect PA operations and incumbents. The SAS would allow GAA users to access spectrum licensed to PA users if it was not being used by the PA licensee.
The FNPRM would provide a "floor" that would ensure that a minimum amount of spectrum was available for nationwide GAA use. The FNPRM would also provide opportunities for Contained Access Users to obtain spectrum for applications within specific facilities (such as buildings) that meet certain criteria to mitigate the potential for interference to and from Incumbent Users and other Citizens Broadband Radio Service users.
Non-federal incumbent users of the spectrum, including 3.6 GHz wireless broadband licensees existing at the time the rules are adopted, would be protected for at least five years after the rules are adopted.
The FNPRM addresses the potential for interference to C-band receive sites. It states: "While the proposed Part 96 rules do not necessarily address all concerns about potential interference into C-Band earth stations raised in the record, they do include stricter-than-normal out-of-band emission limits for CBSDs/user devices, and a spectrum access framework utilizing a dynamic SAS. The SAS can calculate the expected aggregate power flux density at in-band station locations attributable to authorized CBSDs and End User Devices, and authorize operations to ensure that interference protection criteria are not exceeded."
The FNPRM further states: "We seek comment as to whether CBSD and End User Device emission limits based on EPFD and SAS authorization controls would adequately address concerns over potential interference with C-Band earth stations, or whether additional protections are necessary." End-user devices would be permitted to 23 dBm EIRP in 10 MHz. CBSD's would have a baseline power of 30 dBm/10 MHz (1 Watts) and those in rural areas would be able to transmit up to 47 dBm/10 MHz (50 w). Fixed point-to-point systems could use 53 dBm/10 MHz (200 Watts).
The complete set of proposed rules, along with the FCC's explanations for them, are available in the Further Notice of Proposed Rulemaking (FCC 14-49) in the matter of amendment of the Commission's Rules with regard to commercial operations in the 3550-3650 MHz band.
Doug Lung is one of America's foremost authorities on broadcast RF technology. He has been with NBC since 1985 and is currently vice president of broadcast technology for NBC/Telemundo stations.
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