Secrecy Outage Probability of Cooperative Relay Networks with Channel Estimation Error

In this paper, we consider a dual-hop decode-and-forward (DF) relay network which consists of a source, a destination and multiple DF relays in the presence of an eavesdropper, where the source transmits its data to the destination with the help of DF relays while the eavesdropper attempts to tap the relay transmissions. We examine the impact of channel estimation errors on the secrecy performance of source-destination transmissions and propose an optimal relay selection scheme for improving the transmission security against eavesdropping. To be specific, the proposed relay selection is designed by considering the fact that the channel state information (CSI) of any link from the source via DF relays to destination is inaccurate with channel estimation errors. The traditional round-robin relay selection is also considered for comparison purposes. We derive close-form expressions of the secrecy outage probability for both the proposed optimal relay selection scheme and traditional round-robin relay selection schemes. Numerical results demonstrate an adverse effect of the channel estimation errors on the secrecy outage probability of cooperative relay systems. Additionally, it is shown that the proposed optimal relay selection scheme substantially outperforms the traditional round-robin selection approach in terms of the secrecy outage probability.