Abstract: The effect of the untrusted relaying node was investigated on the secrecy outage probability (SOP) of amplify-and-forward (AF) relay networks in the presence of direct links and multiple users. In the considered system, the best user was selected according a certain criterion. It transmitted signals to the destination node with the aid of the untrusted relaying node. To reduce the useful information leakage, three selection criteria were proposed based on the channel state information of the direct and/or relaying link. The closed-form analytical SOP and the corresponding asymptotic expressions were derived. Computer simulation was conducted to validate the theoretical analysis. The SOP performance with the proposed three criterions was compared and their respective diversity orders were proposed.

Key words: secrecy outage probability, amplify-and-forward, relay networks, user selection