June 17, 2015
NTIA’s 2010 Fast Track Report identified the 3.5 GHz band as a possible candidate for spectrum sharing to fulfill the President’s goal of identifying 500 megahertz of additional spectrum for commercial wireless broadband by 2020. It proposed allowing commercial wireless broadband providers to have access to this spectrum where such use would not interfere with critical high-powered shipborne, ground-based, and airborne Department of Defense (DoD) radar systems operating in that band. However, NTIA recognized that if exclusion zones — the areas of the country where commercial use was prohibited — were too large, it would significantly limit the viability of deploying new commercial broadband services in the band. To address this, NTIA engineers from ITS and the Office of Spectrum Management collaborated closely with DoD and FCC staff to minimize the size of these exclusion zones to the greatest extent possible, while still protecting radar operations. This team effort resulted in significant reductions in the size of the exclusion zones — 77% in coastal geographic areas — maximizing the commercial market potential for new broadband services. These results, along with the pioneering regulatory framework that relies on technical solutions to minimize the impact of these zones, are the foundation of the FCC’s new rules.
NTIA Technical Report TR-15-517: 3.5 GHz Exclusion Zone Analyses and Methodology, released June 17, presents the assumptions, methods, analyses, and system characteristics used to generate the maps of the revised exclusion zones. The report provides a description of the technical and deployment parameters of Citizens Broadband Radio Service Device access points and user equipment, technical characteristics of federal radar systems, and the analysis methodology used to compute the distances that established the revised exclusion zones. In particular, the report provides detailed descriptions of the propagation and clutter loss models used to predict transmission loss in a variety of scenarios and the computational methods used to predict aggregate interference power.