Secure transmission using decode-and-forward protocol for underlay cognitive radio networks

In this paper, we study the physical layer security for underlay cognitive radio network in the presence of an eavesdropper that tries to intercept the secondary transmission. Specifically, a transmission at each hop uses a same frequency band of a primary user as long as the interference that caused by the secondary transmission at a primary receiver does not excess a maximum tolerable interference level. We investigate the secrecy outage probability (SOP) for a cognitive decode-and-forward (DF) relay network. Moreover, we drive a closed-form expression of the SOP of the considered system. Simulation results validate our theoretical results under three distinct cases as follows: the signal-to-noise ratio (SNR) of the main link between a secondary transmitter and a corresponding receiver is, respectively, smaller, equal to, or larger than the SNR of the eavesdropper link between the same secondary transmitter and the eavesdropper.