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）与用户中继及同时透射与反射可重构智能表面（STAR RIS）协同增效的优势。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，分别利用中继协议（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）的不同组合。以最大化最小用户速率为目标，我们进一步提出一种基于逐次凸近似（SCA）的统一交替优化（AO）算法，在基站（BS）发射功率约束与STAR RIS能量守恒定律下，联合优化发射端有源波束成形、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包含闭式无源波束成形设计的低复杂度算法。数值结果表明，与未采用STAR RIS的传统CRS方案或其他STAR RIS赋能的多址方案相比，所提框架显著增强了用户公平性。此外，所提低复杂度算法在性能逼近AO方法的同时大幅降低了计算复杂度。