Abstract
In this paper, an underlay cognitive radio system, which consists of a primary-user (PU) transmitter (TX), a PU receiver (RX), a secondary-user (SU) TX, and a SU_RX, is considered.Benneting from the underlay mode, SU_TX can deliver its information to SU_RX by sharing the spectrum resource authorized to PU. It is assumed that SUs are equipped with a single transmitting antenna and a single receiving antenna, which are isolated, and work in full-duplex (FD) mode. By considering that the infor- mation signal transmitted from PU_TX to PU_RX may be eavesdropped by SU_TX if SU_TX is malicious, we investigate the secrecy outage performance of the PU system. The approximated closed-form expression for secrecy outage probability (SOP) and the lower boundary of the asymptotic SOP have been derived and veried by simulation results. Our results reveal the impact of the eavesdropping of the SU and the FD mode adopted at the SU transmitter on the secrecy performance of the PU system in underlay spectrum sharing mode.