In this work, we unveil the advantages of synergizing cooperative rate splitting (CRS) with user relaying and simultaneously transmitting and reflecting reconfigurable intelligent surface (STAR RIS). Specifically, we propose a novel STAR RIS-assisted CRS transmission framework, featuring six unique transmission modes that leverage various combination of the relaying protocols (including full duplex-FD and half duplex-HD) and the STAR RIS configuration protocols (including energy splitting-ES, mode switching-MS, and time splitting-TS). With the objective of maximizing the minimum user rate, we then propose a unified successive convex approximation (SCA)-based alternative optimization (AO) algorithm to jointly optimize the transmit active beamforming, common rate allocation, STAR RIS passive beamforming, as well as time allocation (for HD or TS protocols) subject to the transmit power constraint at the base station (BS) and the law of energy conservation at the STAR RIS. To alleviate the computational burden, we further propose a low-complexity algorithm that incorporates a closed-form passive beamforming design. Numerical results show that our proposed framework significantly enhances user fairness compared with conventional CRS schemes without STAR RIS or other STAR RIS empowered multiple access schemes. Moreover, the proposed low-complexity algorithm dramatically reduces the computational complexity while achieving very close performance to the AO method.

翻译：本文揭示了将协作速率分裂（CRS）、用户中继与同步传输和反射可重构智能表面（STAR RIS）协同融合的优势。具体而言，我们提出了一种新型STAR RIS辅助的CRS传输框架，该框架包含六种独特传输模式，分别采用不同中继协议（包括全双工-FD与半双工-HD）与STAR RIS配置协议（包括能量分裂-ES、模式切换-MS与时间分裂-TS）的组合。以最大化最小用户速率为目标，我们提出了一种基于逐次凸逼近（SCA）的统一交替优化（AO）算法，在基站（BS）发射功率约束与STAR RIS能量守恒定律约束下，联合优化发射有源波束成形、公共速率分配、STAR RIS无源波束成形以及时间分配（针对HD或TS协议）。为降低计算负担，我们进一步提出一种集成闭式无源波束成形设计的低复杂度算法。数值结果表明，相比未采用STAR RIS的传统CRS方案或其他STAR RIS赋能的多址接入方案，所提框架显著提升了用户公平性。此外，所提出的低复杂度算法在逼近AO方法性能的同时，大幅降低了计算复杂度。