Securing full-duplex cognitive relay networks over Nakagami-m fading channels with partial relay selection

In this paper, the secrecy performance of full-duplex underlay cognitive relay networks over Nakagami-m fading channel is studied. The considered system consists of a primary transmitter, multiple primary receivers, a secondary transmitter, multiple secondary full-duplex relays, a secondary destination node, and an eavesdropper. The eavesdropper attempts to over-hear the confidential information in all transmission hops, i.e., from the secondary transmitter to the relay and from the relay to the secondary destination node. In order to enhance the system's secrecy performance, the partial relay selection scheme is applied at the secondary transmitter with the assumption of its partial knowledge of the network's channel state information. Besides, to protect the primary network from the interference of the secondary network, primary network's quality-of-service based constraints for the secondary network's transmit power are established. The exact closed-form expression for the secrecy outage probability of the considered network is derived. The numerical results based on Monte-Carlo simulation are also provided to confirm the correctness of our analysis.