Secure transmission in cognitive radio networks using full-duplex technique with outdated CSI

This paper investigates the effects of the outdated channel state information (CSI) on the secrecy performance of an underlay spectrum sharing cognitive radio networks (CRNs), where the secondary user (SU) source node (Alice) aims to transmit the trusted messages to the full-duplex (FD) aided SU receiver (Bob) with the assistance of cooperative relay (Relay). Considering the impact of feedback delay, outdated CSI will aggravate the system performance. To tackle such challenge, the collaborative zero-forcing beamforming (ZFB) scheme of FD technique is further introduced to implement jamming so as to confuse the eavesdropping and improve the security performance of the system. Under such setup, the exact and asymptotic expressions of the secrecy outage probability (SOP) under the outdated CSI case are derived, respectively. The results reveal that i) the outdated CSI of the SU transmission channel will decrease the diversity gain from min (N
A
N
R
, N
R
N
B
) to N
R
with N
A
, N
R
and N
B
being the number of antennas of Alice, Relay and Bob, respectively, ii) the introduction of FD technique can improve coding gain and enhance system performance.