A critical concern within the realm of visible light communications (VLC) pertains to enhancing system data rate, particularly in scenarios where the direct line-of-sight (LoS) connection is obstructed by obstacles. The deployment of meta-surface-based simultaneous transmission and reflection reconfigurable intelligent surface (STAR-RIS) has emerged to combat challenging LoS blockage scenarios and to provide 360 coverage in radio-frequency wireless systems. Recently, the concept of optical simultaneous transmission and reflection reconfigurable intelligent surface (OSTAR-RIS) has been promoted for VLC systems. This work is dedicated to studying the performance of OSTAR-RIS in detail and unveiling the VLC system performance gain under such technology. Specifically, we propose a novel multi-user indoor VLC system that is assisted by OSTAR-RIS. To improve the sum rate performance of the proposed system, both power-domain non-orthogonal multiple access (NOMA) and rate splitting multiple access (RSMA) are investigated in this work. To realize this, a sum rate maximization problem that jointly optimizes the roll and yaw angles of the reflector elements as well as the refractive index of the refractor elements in OSTAR-RIS is formulated, solved, and evaluated. The maximization problem takes into account practical considerations, such as the presence of non-users (i.e., blockers) and the orientation of the recipient's device. The sine-cosine meta-heuristic algorithm is employed to get the optimal solution of the formulated non-convex optimization problem. Moreover, the study delves into the sum energy efficiency optimization of the proposed system. Simulation results indicate that the proposed OSTAR-RIS RSMA-aided VLC system outperforms the OSTAR-RIS NOMA-based VLC system in terms of both the sum rate and the sum energy efficiency.

翻译：可见光通信（VLC）领域的一个关键问题在于提升系统数据传输速率，尤其是在直射视距（LoS）连接被障碍物遮挡的场景下。基于超表面的同时发射与反射可重构智能表面（STAR-RIS）的部署，已用于应对具有挑战性的LoS遮挡场景，并在射频无线系统中提供360度覆盖。近期，光学同时发射与反射可重构智能表面（OSTAR-RIS）概念被引入VLC系统。本文致力于详细研究OSTAR-RIS的性能，并揭示该技术下VLC系统的性能增益。具体而言，我们提出了一种由OSTAR-RIS辅助的新型多用户室内VLC系统。为提升所提系统的总速率性能，本文研究了功率域非正交多址接入（NOMA）和速率分裂多址接入（RSMA）两种方案。为此，我们构建并求解了一个联合优化OSTAR-RIS中反射元件的滚转角和偏航角以及折射元件的折射率的总速率最大化问题，并对其进行了评估。该最大化问题考虑了实际因素，例如非用户（即阻挡者）的存在以及接收设备的方向。采用正弦余弦元启发算法求解所构建的非凸优化问题的最优解。此外，研究还深入探讨了所提系统的总能量效率优化。仿真结果表明，所提出的OSTAR-RIS RSMA辅助VLC系统在总速率和总能量效率方面均优于基于OSTAR-RIS NOMA的VLC系统。