Secure Transmission in Cognitive Radio Networks Using Full-Duplex Technique with Outdated CSI

This paper investigates the effects ofthe outdated channel state information (CSI) on thesecrecy performance of an underlay spectrum shar-ing cognitive radio networks (CRNs), where the sec-ondary user (SU) source node (Alice) aims to transmitthe trusted messages to the full-duplex (FD) aided SUreceiver (Bob) with the assistance of cooperative re-lay (Relay). Considering the impact of feedback de-lay, outdated CSI will aggravate the system perfor-mance. To tackle such challenge, the collaborativezero-forcing beamforming (ZFB) scheme of FD tech-nique is further introduced to implement jamming soas to confuse the eavesdropping and improve the se-curity performance of the system. Under such setup,the exact and asymptotic expressions of the secrecyoutage probability (SOP) under the outdated CSI caseare derived, respectively. The results reveal that i) theoutdated CSI of the SU transmission channel will de-crease the diversity gain frommin (NANR,NRNB)toNRwithNA,NRandNBbeing the number of anten-nas of Alice, Relay and Bob, respectively, ii) the intro-duction of FD technique can improve coding gain and enhance system performance