Secure transmission in cognitive radio networks using full-duplex technique with outdated CSI

Abstract

In this paper, we investigate the effects of the outdated channel state information (CSI) on the secrecy performance of an underlay spectrum sharing cognitive radio networks (CRNs) with full-duplex (FD) receivers. Legitimate destination node (Bob) acts as a FD node, transmitting interference signals to a passive eavesdropping node (Eve) while receiving signals. To exploit the benefits of collaborative zero-forcing beamforming and FD technologies, transmit antenna selection-maximal-ratio combining-zero forcing beamforming/maximal-ratio transmission-selection combining-zero forcing beamforming (TAS-MRC-ZFB/MRT-SC-ZFB) scheme is considered at the secondary user transmission link with the outdated CSI and collaborative ZFB is adopted at FD destination node, which tries to improve the transmission efficiency of our considered CRNs. Specifically, in order to evaluate the proposed scheme, the derivation of analytical expression in exact and the high asymptotic closed-form expressions of secrecy outage probability (SOP) are provided of the considered network with and without feedback delay of the CSI. Furthermore, the impact of delay on the second user transmission and interference links of the primary user (PU) node is investigated. The results reveal that outdated CSI of secondary user transmission and collaborative ZFB channels deteriorates the SOP, and the outdated CSI between PU and secondary user (SU) will affect the power margin factors for the secondary transmitter. Furthermore, we also study the effects of different system parameters on the secrecy diversity order and secrecy array gain. The proposed scheme is compared with the existing TAS-MRC/TAS-MRC scheme to verify the improvement of system performance. Finally, Monte Carlo simulations verify the correctness of our theoretical analysis.