Secrecy performance analysis of MISO visible light communication systems with spatial modulation

In this paper, we investigate the physical layer secrecy (PLS) problem in the multiple-input single-output (MISO) visible light communication (VLC) system aided by the spatial modulation (SM), which is termed as the MISO SM-VLC system. With addressing the characteristics of channel input signals and MISO SM-VLC scheme, the secrecy performance of MISO SM-VLC system is investigated in detail for the first time, when the input signals obey finite discrete distributions. Specifically, aided by the distribution information of the system's input and output signals, the average mutual information of MISO SM-VLC system is derived. The lower bound and an accurate closed-form expression for approximation of the average mutual information are also obtained, which can be utilized for estimating the achievable secrecy rate of MISO SM-VLC systems efficiently. Moreover, we analyzed the pairwise error probability and bit error rate (BER) of MISO SM-VLC systems, and additionally, some closed-form expressions about the BER and pairwise error probability are obtained. Numerical and simulation results verify the accuracy of the derived theoretical results of the secrecy performance for MISO SM-VLC systems.