Cooperative Beamforming and Jamming for Secure VLC System in the Presence of Active and Passive Eavesdroppers

This paper proposes a novel cooperative beamforming and jamming scheme to deal with passive and active eavesdroppers (EDs) in indoor visible light communication (VLC) networks. An ED in VLC systems can augment its front-end receiver by implementing possible device modifications; thus, jamming is very useful for curbing such an enhanced ED since it would be impossible to distinguish between the information and jamming signals. In contrast to the traditional artificial noise strategies for VLC that can only deal with either passive or active EDs, we propose a combined scheme of beamforming and jamming that significantly improves secrecy performance when both types of EDs exist. The proposed scheme is designed to maximize the signal-to-interference-plus-noise ratio (SINR) of the legitimate receiver, entirely suppress the SINRs of the active EDs, and restrict the average SINR of the passive EDs. We apply an inverse free preconditioned Krylov subspace projection method and the convex-concave procedure to obtain the suboptimal beamforming weight and jamming intensity vectors. Also, an optimal power splitter coefficient is found through the golden section search method. The numerical results verify that the proposed scheme shows superior performance compared to the three benchmarks: 1) zero-forcing beamforming; 2) artificial noise scheme; and 3) enhanced zero-forcing beamforming.