A simultaneously transmitting and reflecting reconfigurable intelligent surface (STAR-RIS) aided communication system is investigated, where an access point sends information to two users located on each side of the STAR-RIS. Different from current works assuming that the phase-shift coefficients for transmission and reflection can be independently adjusted, which is non-trivial to realize for purely passive STAR-RISs, a coupled transmission and reflection phase-shift model is considered. Based on this model, a power consumption minimization problem is formulated for both non-orthogonal multiple access (NOMA) and orthogonal multiple access (OMA). In particular, the amplitude and phase-shift coefficients for transmission and reflection are jointly optimized, subject to the rate constraints of the users. To solve this non-convex problem, an efficient element-wise alternating optimization algorithm is developed to find a high-quality suboptimal solution, whose complexity scales only linearly with the number of STAR elements. Finally, numerical results are provided for both NOMA and OMA to validate the effectiveness of the proposed algorithm by comparing its performance with that of STAR-RISs using the independent phase-shift model and conventional reflecting/transmitting-only RISs.
翻译:同时对一个同时传输和反映可重新配置的智能表面(STAR-RIS)辅助通信系统进行调查,在该系统中,一个接入点向位于STAR-RIS两侧的两个用户发送信息。与目前的工作不同,目前的工作假设是,传输和反射的分档系数可以独立调整,对于纯被动的STAR-RIS而言,这是非三边性的,考虑一种同时传输和反映相容的分档模式。根据这一模式,为非横向多重访问(NOMA)和正方位多重访问(OMA)制定了一个电耗最小化问题。特别是,传输和反射的振幅和分档次变系数是联合优化的,但取决于用户的速率限制。为了解决这一非convex问题,将开发一种高效的、以元素为本的交替优化算法,以便找到一种高质量的亚优解决方案,其复杂性尺度仅与STAR元素的数量线度。最后,为NOMA和OMA提供了数字结果,以验证拟议的算法的有效性,将其性能与Star-RIS-TRIS-RS的常规和移动式模型比较。