Relay selection schemes for decode-and-forward cooperative networks with secrecy constraints

We propose three relay selection schemes for a cooperative network with secrecy constraints, where a decode-and-forward (DF) relaying policy is employed. The first scheme selects the relay having the minimum instantaneous signal-to-noise ratio (SNR) to the eavesdropper, the second one is max-min approach and the third scheme is the optimal selection criteria that maximizes the achievable secrecy rate. We provide a comprehensive analysis and derive closed-form expressions of the secrecy outage probability. Finally, numerical results demonstrate that optimal selection has lowest outage probability, but its performance is only slightly better than that of max-min selection criteria.