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