On physical layer security for reactive DF cognitive relay networks

This paper analyzes the physical layer security for cognitive relay networks under the peak interference power constraint of the primary user receiver. In particular, a secondary user (SU) transmitter communicates with an SU receiver through the help of multiple secondary relays (SRs) using a decode-and-forward (DF) protocol. There exist multiple eavesdroppers (EAVs) who illegally listen to the secondary network communication. We consider a reactive DF scheme, and only the SRs that satisfy a decoding threshold participate in the relay selection. Analytical expressions of the probability of existence of secrecy capacity and secrecy outage probability are obtained. Numerical results are provided to evaluate the impact of the number of SRs, number of EAVs and channel mean powers on the secondary system security. We also investigate the effect of the interference from the primary network to the secondary network performance. Moreover, the performance of proactive DF is analyzed for the purpose of comparison.