On Secrecy Analysis of DF Based Dual Hop Mixed RF-FSO Systems

In this paper, the secrecy performance of a mixed radio frequency-free space optical (RF-FSO) communication system that consists of a source (S), a relay (R), a destination (D), and an eavesdropper (E), is studied. In this system, it is assumed that the E can overhear the free space optical (FSO) link between R and D as it is close to D. It is further assumed that the radio frequency (RF) and FSO links experience Rayleigh and Gamma-Gamma fading, respectively. Considering atmospheric turbulence, pointing errors, two types of detection techniques, and decode-and-forward scheme, the closed-form expressions for the lower bound of secrecy outage probability and the probability of strictly positive secrecy capacity are derived. Monte Carlo simulation results are also presented to validate the accuracy of the derivations.