Fairness Optimization for a Single-LED VLC System Based on Transmitter-and-Channel-Reconfigurable Intelligent Surface

The integration of reflective and transmissive reconfigurable intelligent surfaces (RISs) enables visible light communication (VLC) systems to achieve enhanced performance gains by leveraging their complementary advantages. This paper proposes a transmitter-and-channel (TaC)-RIS-assisted indoor VLC system, where liquid crystal (LC)-based RIS is deployed in front of the light-emitting diode (LED) arrays for emitted light amplification, whereas mirror array (MA)-based RISs are strategically positioned on walls to mitigate line-of-sight (LoS) link blockages. To improve user communication fairness, we formulate a joint optimization problem with the Jain fairness index maximization as the objective function. The sine-cosine-based algorithm (SCA) is employed to solve this problem by simultaneously optimizing the LC RIS refractive index and MARIS mirror orientation angles. Simulations demonstrate that the proposed scheme significantly improves communication fairness through enhanced non-line-of-sight (NLoS) link performance.