Role of Interference-Outage Constraint and Binary Power Control for RIS-Assisted Spectrum Sharing

Considering an reconfigurable intelligent surface (RIS)-assisted underlay spectrum sharing network, our goal is to minimize an average symbol error probability (SEP) of a secondary user while adhering to an interference-outage constraint imposed by a primary user. We first derive an optimal rule for on-off power control at a secondary source and passive beamforming at the RIS to minimize the average SEP at a secondary destination. We derive novel analytical expressions for the probability density functions of the effective interference channel power gains at the primary receiver and primary interference-outage probability. Building upon those analyses, we subsequently propose two simpler, yet near-optimal rules for on-off power control and RIS passive beamforming with lower complexity. Finally, simulation results corroborate the efficacy of the proposed framework and show the impact of different system parameters on the SEP.