Secure Underlay Cognitive Relay Networks in Presence of Primary User's Interference

In this paper, we investigate the secrecy performance of an underlay cognitive decode-and-forward relay network (CDRN) by exploiting an active direct link in the presence of primary user's (PU's) interference. Herein, a secondary user (SU) transmitter strives to maintain a secure communication link with a legitimate SU receiver in presence of a passive eavesdropper. On account of system's viability, we consider the presence of a PU transmitter as well as a PU receiver, wherein the secondary transmissions satisfy the fading-averaged interference constraints at the PU receiver. Specifically, we focus on utilizing the interference from primary transmission as a jamming signal for ameliorating the secrecy performance of secondary network. We derive closed-form expressions of secrecy outage probability for the secondary network with and without PU's interference. Numerical and simulation results validate our analysis and reveal the secrecy performance improvement of considered CDRN.