有源RIS辅助的上行NOMA系统和速率最大化研究

On sum rate maximization for active⁃RIS⁃assisted uplink NOMA systems

可重构智能表面(Reconfigurable Intelligent Surface, RIS)和非正交多址接入(Non-Orthogonal Multiple Access, NOMA)技术都是未来无线通信中有前景的技术。然而,由于基站(Base Station, BS)-RIS-用户之间的反射信道存在“双衰落”效应,会限制传统无源RIS辅助NOMA系统的性能增益。文中针对有源RIS辅助的上行NOMA系统和速率问题展开研究,其中有源RIS的反射单元(Reflecting Elements, REs)不仅可以调整入射信号的相位,也可以放大入射信号的幅度。针对所建立的非凸和速率最大化问题,利用Charnes-Cooper转换和半正定松弛(Semidefinite Relaxation, SDR)工具设计了一种高效的交替优化算法,对优化问题进行求解。仿真结果表明,与多种基准方案相比,文中提出的有源RIS辅助的NOMA系统传输方案可以有效地提高系统的和速率性能。

Both reconfigurable intelligent surface (RIS) and non⁃orthogonal multiple access (NOMA)are treated as promising technologies for future wireless communications. However, the performance gainof a traditional passive RIS⁃aided NOMA system is limited due to the ‘double fading’ effect in thecascaded channel link of the base station (BS)⁃RIS⁃user. In this paper, the sum rate maximizationproblem for uplink NOMA systems assisted by active RIS is studied, in which the reflecting elements(REs) of active RIS can adjust the phase shifts of the incident signal, and amplify the amplitude of theincident signal. In order to deal with the formulated non⁃convex sum rate maximization problem, anefficient alternating optimization algorithm is proposed by leveraging the Charnes⁃Cooper transformationand semidefinite relaxation (SDR) methods. The simulation results show that, compared with severalbenchmark schemes, the proposed transmission scheme for active⁃RIS⁃assisted NOMA systems caneffectively improve the system sum rate.