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On the Physical Layer Security of Multi-user Hybrid RF/VLC Networks

Recently, the hybrid radio frequency (RF)/ visible light communication (VLC) network has been widely studied due to the advantages of high data transmission and no interference between the two networks. Taking the physical layer security (PLS) into account, most work on hybrid RF/VLC network focused on single user. However, many practical scenarios require hybrid network to serve multiple users (MU). Thus, in this paper, we make a study on the PLS of MU hybrid RF/VLC network where the messages to each of the users must be kept confidential from the other and also from the external eavesdropper. To enhance the secrecy performance of the hybrid network, we propose a zero forcing (ZF) beamforming strategy to ensure that the information of each legitimate user can not be received by other users and the eavesdropper. A sum secrecy rate (SSR) optimization problem is formulated under the ZF constraint and the constraint of the power transmitted from the VLC and the RF access point. To reduce the complexity of the original problem, we decouple it into two successive sub-problems and solve them via convex optimization theory and matrix theory. Simulation results show that a positive SSR can always be achieved, and the SSR of the MU hybrid RF/VLC network is superior to that of the standalone RF and VLC networks.