RIS-Based Multi-Beam NOMA: Efficient RIS Partition and Power Control

In this correspondence, we consider a reconfigurable intelligent surface (RIS)-assisted millimeter wave downlink communication system and investigate an efficient RIS partition (RP) based multi-beam (MB) non-orthogonal multiple access (NOMA) transmission scheme. In particular, we develop an asymptotic analytical framework for user effective channel gain (ECG) in conjunction with a practical active-passive beamforming (BF) design, which decouples the complex multi-variable resource allocation problem and enables an efficient joint optimization of RP, BF, decoding order (DO), and power control (PC) for the MB-NOMA. In contrast to existing schemes with high computational complexity, we obtain a closed-form solution for RP. Additionally, we introduce an efficient PC and DO scheme based on asymptotic ECG. Simulation results validate the theoretical analysis and show the advantages of the proposed scheme in terms of complexity and performance.