In this paper, a hybrid non-orthogonal multiple access (NOMA) framework for the simultaneous transmitting and reflecting reconfigurable intelligent surface (STAR-RIS) enhanced cell-edge communication is investigated. Specifically, one transmitted user and one reflected user are paired as one NOMA-pair, while multiple NOMA-pairs are served via time division multiple access (TDMA). The objective is to maximize the minimum downlink rate by jointly optimizing the user pairing, decoding order, passive beamforming, power and time allocation. A novel two-layer iterative algorithm is proposed to solve the highly coupled problem. Simulation results show that: 1) the proposed framework outperforms the conventional reflecting-only-RIS-based and the OMA-based frameworks; 2) the beamforming design and power allocation dominate the achieved performance; 3) increasing the number of passive elements and shortening the distance between BS and STAR-RIS are two effective ways to further improve the performance.

翻译：本文研究了面向同时透射与反射可重构智能表面（STAR-RIS）增强小区边缘通信的混合非正交多址接入（NOMA）方案。具体而言，将一个透射用户与一个反射用户配对构成一个NOMA组，而多个NOMA组通过时分多址（TDMA）方式服务。目标是通过联合优化用户配对、解码顺序、无源波束成形、功率与时间分配，最大化最小下行链路速率。针对这一高度耦合问题，提出了一种新颖的两层迭代算法。仿真结果表明：1）所提框架优于传统仅反射RIS框架及基于OMA的框架；2）波束成形设计与功率分配对性能起主导作用；3）增加无源元件数量与缩短基站到STAR-RIS的距离是进一步提升性能的两种有效途径。