Secrecy outage probability in cognitive radio networks subject to Rayleigh fading channels

Wireless communication systems are vulnerable to eavesdropping attack in which the attacker overhear the transmitted data in the network. Hence, the physical-layer security is of utmost importance to protect the wireless communications against the eavesdropping attack. In this paper, we study the physical-layer security of a two-hops cognitive radio-based communication system where the secondary user sends some confidential information to a destination through a relay. This relay is assumed to be equipped with multiple antennas for reception, applies the maximum-ratio combining technique for the received signals, and uses only one antenna to forward the combined signal to the destination. The transmission is performed under the eavesdropper's attempt to listen to the communication channel. The secrecy outage probability and the intercept probability are both derived based on the statistical characteristics of the channels and under the constraint of avoiding the communication outage of the primary user. All results have been validated using Monte Carlo method.