Sum Rate Maximization of Active RIS-Assisted FD-NOMA Systems

Abstract

This paper is the first to investigate an Active RIS (ARIS)-assisted FD-NOMA system and to formulate a sum rate maximization problem. To address this problem, we propose an alternating optimization algorithm that combines semi-definite relaxation (SDR) and successive convex approximation (SCA) methods. This approach decomposes the original problem into several subproblems, iteratively solving one variable while keeping the others fixed. Specifically, we derive the optimal closed-form solution for the receive beamforming vectors at the BS and propose a method based on SCA and SDR to solve for the transmit beamforming vectors at the BS and the reflection matrix of ARIS. Additionally, the optimal transmit powers for all uplink users are obtained through an iterative algorithm. Simulation results demonstrate that the proposed FD-NOMA scheme significantly enhances the system sum rate compared to HD and OMA schemes. In comparison to passive RIS (PRIS), ARIS effectively mitigates the “double fading effect”, providing a 60%-150% improvement in the rate performance of the assisted communication system.