Rate-Splitting Multiple Access for RIS-Aided Cell-Edge Users With Discrete Phase-Shifts

Abstract

This letter investigates a reconfigurable intelligent surface (RIS)-aided multiple-input-single-output (MISO) communication system which uses rate-splitting multiple access (RSMA) protocol. A multi-antenna base-station (BS) communicates with <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$K$ </tex-math></inline-formula> cell-edge users using RSMA protocol. Each user is assisted with a dedicated RIS. The closed-form expression for the outage probability (OP) is derived considering the discrete and optimal phase-shifts introduced by RIS elements. The interdependent constraints of the threshold and the RSMA factors are derived and analyzed. For getting further insights, the expression for asymptotic OP is derived. Furthermore, the effects of various factors such as number of RIS elements, number of quantization bits, RSMA factors, threshold, etc. are discussed. The correctness of the derived expressions is validated using the Monte-Carlo simulations.