Reconfigurable Intelligent Surface-Assisted Non-Orthogonal Multiple Access

Reconfigurable intelligent surface (RIS) is a revolutionary technology to achieve spectrum-, energy-, and cost-efficient wireless networks. This paper considers an RIS-assisted downlink non-orthogonal-multiple-access (NOMA) system. To optimize the rate performance ensure user fairness, we maximize minimum decoding signal-to-interference-plus-noise-ratio (equivalently rate) of all users, by jointly optimizing (active) transmit beamforming at base station (BS) phase shifts (i.e., passive beamforming) RIS. A combined-channel-strength based user-ordering scheme for NOMA first proposed decouple design joint design. Efficient algorithms are further solve non-convex problem, leveraging block coordinated descent semidefinite relaxation (SDR) techniques. For single-antenna BS setup, optimal power allocation asymptotically RIS obtained in closed forms. multiple-antenna it shown that rank SDR solution upper bounded two. Also, analyzed terms convergence complexity. Simulation results show system can enhance significantly, compared traditional without orthogonal multiple access with/without