Optical RIS-collaborative beamforming: A high-efficiency covertness enhancement scheme for VLC system

Abstract

Due to the susceptibility to blockage and vulnerability to eavesdropping, the security of the visible light communication (VLC) system faces challenges. To address this issue, this paper proposes a liquid crystal-digital reconfigurable intelligent surface (LC-DRIS)-assisted covert VLC system with collaborative active transmit beamforming and passive reflect beamforming. First, we model the multiple-input single-output (MISO) covert communication system assisted by LC-DRIS and rigorously derive the corresponding covertness constraints. Then, an optimization problem is formulated to jointly optimize the beamforming vectors and LC-DRIS configurations. An alternating optimization framework is proposed to decouple the problem into two subproblems, which are finally handled by the zero-forcing scheme and the genetic algorithm (GA), respectively. The numerical simulation results show that the introduction of LC-DRIS significantly enhances the achievable covert transmission rate for the VLC system.