Generalized Relay Selection for Improved Security in Cooperative DF Relay Networks

In this letter, a generalized multi-relay selection scheme is proposed to improve the security in a cooperative relay network. Assuming that only the statistical channel state information of the eavesdropper is available at the transmitter, a semiclosed-form expression of the secrecy outage probability (SOP) is derived. Based on this, both the power allocation factor and the number of relay nodes are jointly optimized to minimize the SOP. Simulation results show that the proposed multi-relay selection scheme outperforms the conventional single-relay selection scheme without increasing the overhead.