OSTAR-RIS-Assisted Secure and High-Coverage NOMA Transmission for Multi-User VLC Systems

Visible light communication (VLC) has been recognized as an energy-efficient, and low-cost technology for high-speed next-generation communication systems. However, it has been observed that the performance of a VLC-based system is limited by low coverage area, and loss of the VLC signal due to the absence of a direct link between the transmitter and the receiver caused by blockages present in the environment. In addition, the secrecy sum rate (SSR) of a multi-user VLC system is also compromised by the presence of an eavesdropper. To address the problem of dead zones and low coverage areas, an optical simultaneously transmitting and reflecting intelligent surface (OSTAR-RIS) has been proposed in the literature. To improve the SSR performance of a multi-user OSTAR-RIS-assisted VLC systems, the application of non-orthogonal multiple access (NOMA) is considered in this work. For SSR maximization, particle swarm optimization (PSO) is employed to jointly optimize the roll and yaw angles of the mirror array (MA), the refractive index of the refractor elements in the liquid crystal (LC) array and the power allocation factor of NOMA. The performance of NOMA OSTAR-RIS VLC is compared with the benchmark methods. Simulations illustrate superiority of the proposed optimization technique over benchmark schemes in NOMA OSTAR-RIS-aided multi-userVLC systems.