  The paradigm of shared spectrum allows secondary devices to opportunistically
access spectrum bands underutilized by primary owners. Recently, the FCC has
targeted the sharing of the 3.5 GHz (3550-3700 MHz) federal spectrum with
commercial systems such as small cells. The rules require a Spectrum Access
System (SAS) to accommodate three service tiers: 1) Incumbent Access, 2)
Priority Access (PA), and 3) Generalized Authorized Access (GAA). In this work,
we study the SAS-assisted dynamic channel assignment (CA) for PA and GAA
tiers.We introduce the node-channel-pair conflict graph to capture pairwise
interference, channel and geographic contiguity constraints, spatially varying
channel availability, and coexistence awareness. The proposed conflict graph
allows us to formulate PA CA and GAA CA with binary conflicts as
max-cardinality and max-reward CA, respectively. Approximate solutions can be
found by a heuristic-based algorithm that search for the maximum weighted
independent set. We further formulate GAA CA with non-binary conflicts as
max-utility CA. We show that the utility function is submodular, and the
problem is an instance of matroid-constrained submodular maximization. A
polynomial-time algorithm based on local search is proposed that provides a
provable performance guarantee. Extensive simulations using a real-world Wi-Fi
hotspot location dataset are conducted to evaluate the proposed algorithms. Our
results have demonstrated the advantages of the proposed graph representation
and improved performance of the proposed algorithms over the baseline
algorithms.
