Tri-Level BCD Optimization in OIRS-Assisted MIMO-VLC for Enhanced Physical-Layer Security

This letter addresses the physical-layer security (PLS) challenge in multi-input multi-output (MIMO) visible light communication (VLC) systems. Existing solutions often overlook VLC-specific constraints and fail to jointly optimize key parameters. To overcome this, we propose an optical intelligent reflecting surface (OIRS)-assisted tri-level optimization framework that simultaneously handles power allocation, OIRS assignment, and orientation control. A block coordinate descent approach incorporating convex approximation, greedy heuristics, and metaheuristic search is developed. Simulation results confirm significant secrecy rate improvement and robustness under various conditions and imperfect channel knowledge.