This paper proposes a new transmit antenna selection (TAS) scheme whichprovides enhanced physical layer security in multiple-input multiple-output(MIMO) wiretap channels. The practical passive eavesdropping scenario weconsider is where channel state information (CSI) from the eavesdropper is notavailable at the transmitter. Our new scheme is carried out in two steps.First, the transmitter selects the first two strongest antennas based on thefeedback from the receiver, which maximizes the instantaneous signal-to-noiseratio (SNR) of the transmitter-receiver channel. Second, the Alamouti scheme isemployed at the selected antennas in order to perform data transmission. At thereceiver and the eavesdropper, maximal-ratio combining is applied in order toexploit the multiple antennas.We derive a new closed-form expression for thesecrecy outage probability in nonidentical Rayleigh fading, and using thisresult, we then present the probability of non-zero secrecy capacity in closedform and the {\epsilon}-outage secrecy capacity in numerical form. Wedemonstrate that our proposed TAS-Alamouti scheme offers lower secrecy outageprobability than a single TAS scheme when the SNR of the transmitter-receiverchannel is above a specific value.
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