Effect of Federal Incumbent Activity on CBRS Commercial Service

Abstract

Federal Communications Commission rules for the 3.5 GHz citizens broadband radio service (CBRS) permit commercial systems to share 150 MHz of bandwidth with federal and other incumbents. To protect the federal incumbents, a spectrum coordinator—the spectrum access system (SAS)—uses a standardized algorithm to suspend some commercial transmissions when a nearby incumbent (e.g., a shipborne radar) becomes active. Using propagation models based on those employed by the SAS for interference management, this paper quantifies the impact of federal incumbent activity on commercial service, in terms of both the numbers of transmissions affected and their service area. These metrics are also used to examine the tradeoff between commercial coverage and immunity to incumbent activity as a function of commercial base station antenna height. We find that, in some cases, the reduction in coverage from lowering antenna heights is more than offset by the gain in immunity to incumbent activity.