Secure Beamforming Design for Multi-Color Visible Light Communication Systems

Abstract

Visible light communication (VLC), offering high bandwidth and resisting electromagnetic interference, is a promising optical wireless communication technology for next-generation wireless communication systems (NG-WCS). On the other hand, multi-color VLC (MC-VLC), enabling the use of wavelength-division multiplexing by exploiting multiple wavelengths within the visible spectrum, offers significant potential for high-speed data transmission, which plays a critical role in addressing the ultra-low latency demands in NG-WCS. Data security is crucial in NG-WCS due to the rapid expansion of Internet of Things (IoT) devices and the rise of ultra-low-latency and mission-critical applications. The literature on physical layer security (PLS), which plays a pivotal role in enabling data security, is limited for MC-VLC systems, and existing studies do not consider the impact of inter-color interference (ICI). Considering ICI, this paper focuses on solving the secrecy rate maximization problem in MC-VLC systems that use beamforming PLS techniques. The optimization problems are formulated to find optimal beamformers maximizing the secrecy rates in MC-VLC systems for the cases of no-ICI and ICI, resulting in non-convex and NP-hard problems. This paper proposes ZF beamforming designs that facilitate implementations into practical MC-VLC systems by converting non-convex optimization problems into easily solvable linear programming problems. Numerical results show that the proposed ZF beamformer achieves the optimal solution in the no-ICI case and remains near-optimal in the ICI case when optical filters with appropriate passband boundaries, effectively attenuating ICI, are used. Additionally, the proposed designs provide higher secrecy rates than traditional ZF beamformers.