  Spectrum access system (SAS) is widely considered the de facto solution to
coordinating dynamic spectrum sharing (DSS) and protecting incumbent users. The
current SAS paradigm prescribed by the FCC for the CBRS band and standardized
by the WInnForum follows a centralized service model in that a spectrum user
subscribes to a SAS server for spectrum allocation service. This model,
however, neither tolerates SAS server failures (crash or Byzantine) nor resists
dishonest SAS administrators, leading to serious concerns on SAS system
reliability and trustworthiness. This is especially concerning for the evolving
DSS landscape where an increasing number of SAS service providers and
heterogeneous user requirements are coming up. To address these challenges, we
propose a novel blockchain-based decentralized SAS architecture called BD-SAS
that provides SAS services securely and efficiently, without relying on the
trust of each individual SAS server for the overall system trustworthiness. In
BD-SAS, a global blockchain (G-Chain) is used for spectrum regulatory
compliance while smart contract-enabled local blockchains (L-Chains) are
instantiated in individual spectrum zones for automating spectrum access
assignment per user request. We hope our vision of a decentralized SAS, the
BD-SAS architecture, and discussion on future challenges can open up a new
direction towards reliable spectrum management in a decentralized manner.
