Joint Optimization of Precoding and Probabilistic Constellation Shaping for Physical Layer Security in Visible Light Communications

The inherent broadcast nature of the light signal requires robust security solutions against eavesdropping attacks for visible light communications (VLC). Aside from conventional cryptography, physical layer security (PLS) is a novel paradigm to protect information confidentiality. This paper proposes a joint design of precoding and probabilistic constellation shaping (PCS) for enhancing the performance of PLS in multiple-input single-output (MISO) VLC systems. Specifically, the proposed design aims to optimize the secrecy capacity while ensuring the reliability of the channel of the legitimate user. The optimal design is shown to be a non-linear and non-convex problem that is difficult to solve using classical optimization techniques. Therefore, a hybrid particle swarm optimization (PSO) and genetic algorithm (GA) are employed to tackle the problem. Simulation results demonstrate that compared with the precoding-only design, the proposed joint design achieves a better secrecy capacity (especially at the low optical power region) and can guarantee the reliability of the legitimate user’s channel over the examined optical power region.