Achievable secrecy capacity in an underlay cognitive radio network

In this paper, we consider a spectrum sharing cognitive radio network where a secondary user (SU) transmitter (SU-Tx) communicates with multiple SU receivers (SU-Rxs). There exist multiple eavesdroppers (EAVs) who illegally listen to the secondary network communication. Further, the primary network consists of a primary user (PU) transmitter serving multiple PU receivers. In particular, the SU-Tx transmit power is subject to the joint constraint of PU outage and SU maximum transmit power limit. Moreover, we investigate the secondary network physical layer security in terms of average secrecy capacity for both cases of known and unknown channel information of the EAV at the SU-Tx. Numerical results are provided to evaluate the impact of the number of PU-Rxs, number of EAVs, number of SU-Rxs, and channel mean powers among users on the SU average secrecy capacity.