Secrecy outage on transmit antenna selection/maximal ratio combining in MIMO cognitive radio networks

This paper investigates the secrecy outage performance of transmit antenna selection (TAS)/maximal ratio combining (MRC) in multiple input multiple output (MIMO) cognitive radio networks (CRNs) over Rayleigh fading channels. In the considered system, a secondary user (SU-TX) equipped with N
_A
(N
_A
≥ 1) antennas uses TAS to transmit confidential messages to another secondary user (SU-RX), which is equipped with N
_B
(N
_B
≥ 1) antennas and adopts MRC scheme to process multiple received signals. Meanwhile, an eavesdropper equipped with N
_E
(N
_E
≥ 1) antennas also adopts MRC scheme to overhear the transmitted information between SU-TX and SU-RX. SU-TX adopts the underlay strategy to guarantee the quality of service of the primary user without spectrum sensing. In this paper, we derive the closed-form expression for the secrecy outage probability (SOP) and propose a simplified SOP when the maximum transmit power at SU-TX is always sufficiently high. Finally, simulations are conducted to validate the accuracy of our proposed analytical models.