Sum Rate and Fairness Optimization in RIS-Assisted VLC Systems

Abstract

The use of visible light communication (VLC) to support wireless coverage has been receiving increasing interest, due to factors that include its operation in a large unregulated spectrum and immunity against electromagnetic interference. On the other hand, the sensitivity of VLC network performance to the line-of-sight (LOS) link quality affects the system reliability. The emergence of reconfigurable intelligent surfaces (RISs) in optical domain opens the door for minimizing the impacts of the LOS link degradation on VLC networks, given the possibilities they provide for enhancing the non-LOS channel gain. In this paper, we propose optimizing the RIS-assisted VLC systems by controlling the RIS elements to maximize the network sum-rate while maintaining fairness in the user achievable throughput. Two types of RIS elements are considered, where the addressed non-convex optimization problems are handled using the genetic algorithm and the particle swarm optimization techniques, presenting improvement in network performance in terms of sum rate, fairness, and link outage ratio. In addition, we investigate the RIS-assisted VLC system performance in cases of handling mobile users, highlighting the trade-off between the variation in the optimization rate and the network performance.