Secrecy Cooperative Networks with Outdated Relay Selection over Correlated Fading Channels

In this paper, we study the impact of correlated fading on the secrecy performance of multiple decode-and-forward (DF) relaying with outdated relay selection. It is assumed that the information transmission, assisted by $N$ DF relays from the source to the destination, can be overheard by an eavesdropper. Particularly, we consider the realistic scenario where the eavesdropper's and the main channels are correlated. In order to enhance the network security, the best relay is selected among $N$ available DF relays to assist the secure transmission. Due to the time-varying channel environments, we note that the selected relay may be outdated. In order to study the impact of both channel correlation and outdated relay selection on the secrecy performance, we first derive an analytical expression for the secrecy outage probability (SOP). Also, we derive the asymptotic expression for the SOP in the high main-to-eavesdropper ratio regime. Numerical results are provided to demonstrate the correctness of our analytical expressions.