Joint Beamforming and Power Splitting Optimization for RIS-Assited Cooperative SWIPT NOMA Systems

Abstract

In this paper, reconfigurable intelligent surface (RIS) is utilized to enhance the performance of the cooperative non-orthogonal multiple access (C-NOMA). The simultaneous wireless information and power transfer (SWIPT) technology is adopted at the cell-center user to relay information to the cell-edge user. We aim to maximize the data rate of the cell-edge user by jointly optimizing the beamforming vectors, the reflecting phase shifts, the power splitting (PS) ratio and the relaying power under the energy constraint and minimum data rate constraint of the cell-center user. To solve the established non-convex problem, an iterative algorithm based on alternate optimization is proposed to decompose the original problem into three sub-problems. In addition, successive convex approximation (SCA) and semi-definite relaxation (SDR) techniques are also employed to solve the sub-problems. Simulation results illustrate that the proposed RIS-assisted cooperative SWIPT NOMA scheme can effectively improve the performance of the cell-edge user compared with the traditional scheme without RIS.