Joint Active and Passive Beamforming Optimization in Self-sustainable RIS-aided NOMA Networks

Reconfigurable Intelligent Surface (RIS) is a competitive technology for future communication systems owning its capability of artificially manipulating the Electro-Magnetic (EM) environment at a low energy cost. Self-sustainable RIS, as a practical design, further enhance the ease of deploying and maintaining the devices. In this paper, we discuss the joint active and passive beamforming design of a Wireless Power Transfer (WPT) powered self-sustainable RIS aided Non-Orthogonal Multiple Access (NOMA) system. An RIS-NOMA transmission scheme and a corresponding min-max fairness problem are proposed. To address the problem and tackle the non-convexity caused by the coupling of active and passive beamforming parameters, we discuss an Alternating Optimization (AO) based solution. Results show the tradeoff between self-sustainability and Spectrum Efficiency (SE) under different RIS settings. It is also determined that self-sustainable RIS and NOMA are mutual beneficial and allow higher SE compared with the combination with traditional OMA schemes.