On Secrecy Performance of Mixed RF-FSO Systems With a Wireless-Powered Friendly Jammer

This paper presents a study of the physical layer security performance of a mixed radio frequency-free space optical (RF-FSO) system with a wireless-powered friendly jammer. The RF links undergo the Nakagami-m fading, and the FSO link experiences the Exponentiated Weibull (EW) distribution. A two-hop decode-and-forward (DF) relay is present in the system. A single-antenna eavesdropper located on the RF link attempts to eavesdrop on the channel transmission information. There is a nearby multi-antenna jammer that can be charged wirelessly, and a save-then-transmit (ST) protocol is introduced in the jammer. The closed expressions for the secrecy outage probability (SOP) and the average secrecy capacity (ASC) of the mixed RF-FSO system are derived, and the correctness of the expressions is verified using the Monte-Carlo method. The influence of various key factors on the secrecy performance of the system is analyzed by simulations. The results show that increasing the average interference noise ratio, the number of interferer antennas, the time block allocation factor, and the size of the receiving aperture has a significant effect on the secrecy performance. This study provides a new system structure and a good theoretical basis for evaluating the physical layer security performance of mixed RF-FSO systems.