This paper investigates the extent to which spectrum sharing in mmWavenetworks with multiple cellular operators is a viable alternative totraditional dedicated spectrum allocation. Specifically, we develop a generalmathematical framework by which to characterize the performance gain that canbe obtained when spectrum sharing is used, as a function of the underlyingbeamforming, operator coordination, bandwidth, and infrastructure sharingscenarios. The framework is based on joint beamforming and cell associationoptimization, with the objective of maximizing the long-term throughput of theusers. Our asymptotic and non-asymptotic performance analyses reveal five keypoints: (1) spectrum sharing with light on-demand intra- and inter-operatorcoordination is feasible, especially at higher mmWave frequencies (for example,73 GHz), (2) directional communications at the user equipment substantiallyalleviate the potential disadvantages of spectrum sharing (such as highermultiuser interference), (3) large numbers of antenna elements can reduce theneed for coordination and simplify the implementation of spectrum sharing, (4)while inter-operator coordination can be neglected in the large-antenna regime,intra-operator coordination can still bring gains by balancing the networkload, and (5) critical control signals among base stations, operators, and userequipment should be protected from the adverse effects of spectrum sharing, forexample by means of exclusive resource allocation. The results of this paper,and their extensions obtained by relaxing some ideal assumptions, can provideimportant insights for future standardization and spectrum policy.
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