Binary Power Control and Passive Beamforming for RIS-Assisted Spectrum Sharing Network
Priyanka Das, Sumukha Kashyap, Rimalapudi Sarvendranath, Amrita Mishra · 2023
Underlay spectrum sharing is an effective solution to improve the spectral efficiency of wireless communications systems by allowing a secondary user (SU) to share spectrum with a primary user (PU). Meanwhile, reconfigurable intelligent surface (RIS) has been recently emerged as a promising technique to enhance energy efficiency through intelligently reconfiguring the channel environment. However, it is challenging to achieve higher quality of service for the SU under strict interference constraints to protect the PU. Therefore, adapting the transmit power of the SU and phases of RIS reflective elements while adhering to constraints on the interference caused to the PU is crucial. This adaptation is driven by the nature of interference and transmit power constraints imposed on the SU. For an RIS-assisted secondary network, we aim to minimize an average symbol error probability subject to an average interference constraint imposed by the PU. We systematically develop an optimal rule for joint binary transmit power control for the SU and passive beamforming for the RIS. We propose an algorithm to find optimal Lagrange parameter. We also propose a low-complexity coordinate descent based iterative algorithm to obtain RIS phase shifts. Simulation results demonstrate the efficacy of the optimal rule compared to several benchmarking rules.