Improving secrecy for multi-relay multi-eavesdropper wireless systems through relay selection

In this paper, we consider a cooperative relay network consisting of a source, a destination and multiple decode-and-forward relays in the presence of multiple eavesdroppers, which intend to tap confidential messages transmitted by both the source and relays. We propose both the so-called secrecy maximisation oriented relay selection (SMORS) and multi-relay oriented relay selection (MRORS) schemes to improve the physical layer security of wireless communications. In the SMORS scheme, a single relay with the maximal secrecy rate is selected among all the decode-and-forward relays to forward the source signal. By contrast, in the MRORS scheme, the relays that succeed in decoding the source signal will be employed to simultaneously forward their decoded signals to the destination. We analyse the intercept probability of the SMORS and MRORS schemes as well as the traditional max–min relay selection scheme. It is shown that the proposed MRORS scheme outperforms the SMORS and max–min relay selection schemes in terms of the intercept probability. Additionally, it is shown that with an increasing number of eavesdroppers, the intercept performance of wireless communications degrades, which can be well addressed using the SMORS and MRORS schemes through increasing the number of relays. By contrast, increasing the number of relays has little impact on the intercept probability for the conventional max–min relay selection scheme Transactions on Emerging Telecommunications Technologies. Copyright © 2016 John Wiley & Sons, Ltd.