Secrecy performance analysis of relay selection in adaptive DF relaying network with active adversary

In this paper, we derive and compare the performance of relay selection strategies presence of an active adversary under a cooperative setting. The system consists of a source, a destination, multiple decode-and-forward relays and an active eavesdropper. These DF relays correctly decode source message, if their signal-to-noise ratio is above a certain threshold. The channels experience independent but not identical Rayleigh fading. We assume both source and eavesdropper can exploit direct and relaying channel. Two relay selection schemes are performed by the eavesdropper, which is assumed to be a part of the system and active. A conventional all-performing relays (using maximal ratio combining) scheme is compared with the above mentioned schemes. We obtain closed-form expressions for the secrecy outage probability of these three strategies. An asymptotic analysis is presented only when relay selection is performed by the eavesdropper. From numerical results, it is observed that relay selection performed by the active eavesdropper proves to be the worst from the perspective of legitimate receiver. Also restriction on either of the two hops results in flooring of secrecy performance.