In this paper, we introduce transmit antenna selection/maximal-ratio combining (TAS/MRC) scheme in dualhop randomize-and-forward (RaF) cognitive multiple-input multiple-output (MIMO) wiretap networks with outdated channel state information (CSI). In this network, the secondary transmitter adopts TAS scheme to choose the antenna with the maximal received signal-to-noise ratio (SNR), while the secondary receiver and eavesdropper adopt MRC scheme to combine the received signals. To thoroughly assess the secrecy performance achieved by TAS/MRC scheme and the impact of outdated CSI onthe secrecy performance, we derive a new closed-form expression for the secrecy outage probability of dual-hop RaF cognitive MIMO wiretap networks. In order to achieve more insights on the application of TAS/MRC scheme, we further present tractable asymptotic secrecy outage probability at high SNR regimes under two distinct scenarios. From our analysis, several important concluding remarks are obtained as follows: a) The RaF relaying strategy achieves better secrecy performance than that of the decode-and-forward (DF) relaying strategy for dual-hop cognitive MIMO wiretap networks, b) Outdated CSI decreases the secrecy diversity gain of TAS/MRC scheme from NR min (NA, NB) tomin (NR, NB), c) Although TAS/MRC scheme can not attain full secrecy diversity gain for the considered system with outdated CSI, it still can achieve an extra secrecy coding gain compared with random antenna selection/MRC (RAS/MRC) scheme.
Zhang, T., Cai, Y., Huang, Y., Duong, Q., & Yang, W. (2016). Secure Transmission in Cognitive MIMO Relaying Networks With Outdated Channel State Information. IEEE Access. https://doi.org/10.1109/ACCESS.2016.2608966