Secrecy sum-rate of multi-user MISO visible light communication systems with confidential messages

This paper studies the information theoretic secrecy sum-rate for multi-user multiple-input single-output (MU-MISO) visible light communication (VLC) systems with confidential messages. The well-known zero-forcing (ZF) precoding technique is employed to ensure confidentiality among legitimate users and, at the same time, to prevent eavesdropper(s) from obtaining any information. Different from radio frequency (RF) counterpart where the average input power constraint is usually imposed on the derivation of channel capacity, the input data signal of VLC systems is amplitude constrained, leading to a peak input power constraint. The amplitude constraint gives rise to the complexity in obtaining an analytical expression for the capacity. In this paper, we analytically investigate a novel bound on the secrecy sum-rate of all legitimate users in MU-MISO VLC systems, which is valid in high signal-to-noise ratio (SNR) regime. The secrecy sum-rate performance is then derived for two scenarios: known and unknown eavesdropper's channel state information (CSI) at the transmitter.