相移耦合的STAR-RIS辅助NOMA通信系统低功耗传输方案研究

A low-power transmission scheme for NOMA communication system assisted by phase-coupled STAR-RIS

同时透射和反射的可重构智能表面(Simultaneously Transmitting and Reflecting Reconfigurable Intelligent Surface,STAR-RIS)是未来B5G/6G无线通信的创新技术,其与非正交多址接入(Non-Orthogonal Multiple Access,NOMA)技术结合可大幅提升通信系统的频谱与功率效率,成为当前无线通信研究的热点。目前关于STAR-RIS的研究主要集中于透射相移和反射相移相互独立的场景,忽略了在电路实现过程中透射相移和反射相移之间的耦合效应。针对更加实际的相移耦合STAR-RIS辅助NOMA通信系统展开研究,建立了基站波束成形、相移与振幅系数的联合优化问题。通过使用连续凸逼近(Successive Convex Approximation,SCA)和半正定松弛(Semidefinite Relaxation,SDR)等技术工具,设计了高效的STAR-RIS单元间的交替优化算法,求解STAR-RIS辅助的NOMA下行传输功率最小化问题。仿真结果表明,提出算法的性能明显优于传统的反射RIS方法,且接近理想的独立相移STAR-RIS辅助系统。

Simultaneously transmitting and reflecting reconfigurable intelligent surface(STAR-RIS)is regarded as an innovative technology for future B5G/6G wireless communications.It can be combined with non-orthogonal multiple access(NOMA)to enhance both the spectrum and the power efficiency substantially.Thus,the combination of STAR-RIS and NOMA has become a hot topic in the research of wireless communications.However,most of the existing literature on STAR-RIS focuses on the scenario with independent phase shifts,which ignores the coupling effects between the transmitting and the reflecting phase shifts in the practical realizations.In regard of this,this paper studies the STAR-RIS assisted NOMA communication system with coupled phase shifts,and formulates a joint optimization problem of beamforming at the base station,phase shifts,and amplitude coefficients.By using the successive convex approximation(SCA)and the semidefinite relaxation(SDR)tools,we design an effective alternating optimization algorithm to address the power minimization problem for the downlink STAR-RIS aided NOMA system.Simulation results show that the proposed scheme outperforms the traditional reflection-only RIS method.In addition,the performance of the proposed scheme is very close to that of the ideal STAR-RIS system with independent phase shifts.