  The Citizens Broadband Radio Service (CBRS) recently adopted in the U.S.
enables two tiers of commercial users to share spectrum with a third tier of
incumbent users. This sharing can be further assisted by Environmental Sensing
Capability operators (ESCs), that monitor the spectrum occupancy to determine
when use of the spectrum will not harm incumbents. Two key aspects of this
framework that impact how firms may compete are the differences in information
provided by different ESCs and the different tiers in which a firm may access
the spectrum. We develop a game theoretic model that captures both of these
features and analyze it to gain insight into their impact. Specifically, we
consider a priority access (PA) tier firm has access to the both licensed band
and unlicensed band, and a general authorized access (GAA) tier firm has access
only to the unlicensed band. The PA tier and GAA tier firms compete for users.
Our analysis reveals that the amount of unlicensed and licensed bandwidth in
the CBRS must be chosen judiciously in order to maximize the social welfare. We
also show that a limited amount of unlicensed access of PA tier firm is
beneficial to the user's surplus as well as to the social welfare.
