Evaluating the CBRS Experiment
Abstract
In 2015, the FCC established the Citizens Broadband Radio Service (CBRS) for sharing the 3.5 GHz Band (3550-3700 MHz) among federal and non-federal users in the United States. This rulemaking created an experiment in a novel three-tier rights structure: strong protections for incumbents, including government radar systems; Priority Access Licenses (PALs) granting exclusive rights to high bidders in an FCC auction, in part of the band and subject to avoiding interference with incumbents; and Generalized Authorized Access (GAA) for unlicensed users, subject to avoiding interference with both PALs and incumbents. The first commercial deployments in this band were approved in 2019 for GAA devices, and an auction of PALs completed in 2020 generated $4.5 billion in revenues.
It is now timely to evaluate this experiment and glean lessons for applications to other spectrum bands, such as the neighboring 3.1-3.45 GHz band or portions of the upper mid-band spectrum 7-24 GHz. In fact, a number of perspectives on CBRS have been recently published. In this paper we review these developments and suggest related policy questions that should be considered when evaluating the use of CBRS-style allocation rules in future bands.
The CBRS policy involves several different innovations, seeking to accomplish multiple objectives. One can evaluate this approach from a technical point of view, as an experiment to show that dynamic sharing can provide multiple tiers of commercial access to a band of spectrum while protecting incumbent users. The approach involves coordinated access via a cloud-based Spectrum Access System (SAS) and an Environmental Sensing Capability (ESC) to monitor incumbent users of the band, with requirements standardized through the Wireless Innovation Forum (WInnForum) and implementations certified by the FCC. From an economic and policy point of view, this type of dynamic sharing is asserted to reduce the costs and delays involved in making additional spectrum available for commercial use, as it seeks to avoid relocating incumbents. Of course, costs and benefits should be observed, not simply assumed, and the process undertaken should be compared to those associated with the relevant policy alternatives.
CBRS adopted the PAL and GAA tiers for commercial access in an attempt to provide spectrum that could not only support deployments by traditional wireless providers, but also enable new uses of the spectrum by non-traditional entities. How well the spectrum can support these uses, and whether this type of approach leads to an economically efficient mix of uses, provides another economic and policy lens through which this system can be evaluated. This paper explores the technical implementation of the CBRS spectrum sharing approach, and then attempts to appraise the economic welfare results of the novel allocation policy.