Abstract
The recently established Citizens Broadband Radio Service (CBRS) has
attracted attention because it accommodates incumbents, auctioned
license holders, and unlicensed users. Incumbents retain unconstrained
transmission rights, but when inactive, the unused spectrum is shared
between the Primary Access License (PAL) users and the General
Authorized Access (GAA) users. The spectrum sharing is controlled by a
cloud-based centralized administrator, Spectrum Access System (SAS),
which uses an environmental sensing capability network to establish
transmission rights for PAL and GAA users without hindering the
incumbents. This paper reports findings from GAA CBRS Devices’ (CBSDs’)
deployments in California’s San Diego county, which has numerous
incumbents and characterizes the temporal and spatial behavior of CBRS.
Based on measured temporal data, a Markov model is shown to be effective
in estimating the steady state and hitting time probabilities for
spectrum availability. We also recorded the availability of the CBRS
spectrum, advertised by the SAS at various locations in San Diego, and
found evidence of undisclosed obfuscation in the reporting of spectrum
availability. We then developed two strategies that maximize the entropy
of the Markov Chain’s hidden states and provide more significant
obfuscation than the undisclosed actions of the SAS.