Coordination of Energy and Information Precoding for NOMA-based WPCNs Aided by Reconfigurable Intelligent Surface

Abstract

In wireless powered communication networks (WPCNs), the wireless energy acquisition is weak due to the fading characteristic of wireless link, which is hard to supply the energy. Reconfigurable intelligent surface (RIS) is a promising performance enhancement technology for WPCNs, which can improve the energy and spectral efficiency, expand the network coverage, and thus improve the throughput. This paper proposes a new framework for energy harvesting and information transmission of non-orthogonal multiple access (NOMA)-based WPCNs aided by the RIS. The total transmission capacity is maximized by joint optimization of energy precoding, information precoding, and the phase shift of RIS, which turns out to be a non-convex problem. So we propose a joint optimization algorithm combing alternating optimization (AO), semidefinite relaxation (SDR), and successive convex approximation (SCA) methods, which is called ASS algorithm for short. Numerical results prove that the throughput of the multi-user system can be significantly improved.