Physical layer security of MISO TAS wiretap channels with interference-limited eavesdropper

This paper investigates the secrecy performance of multiple-input single-output (MISO) wiretap channels with transmit antenna selection (TAS) and subject to an interference-limited eavesdropper. By considering N_A antennas at the transmitter, a single antenna at the legitimate receiver and eavesdropper, and multiple arbitrary co-channel interferers M at the eavesdropper, an exact closed-form expression for the secrecy outage probability is derived. The exact expression is simplified for two, yet novel, special cases. Based on these analytical expressions, an asymptotic secrecy outage analysis is carried out and it shows that the diversity order of the considered system equals to min(N_A, M). The proposed analysis is corroborated through Monte Carlo simulation results. Illustrative numerical examples are depicted and insightful discussions are drawn. It is shown that the secrecy outage performance is largely limited by the number of interference channels and the number of transmit antennas due to diversity gain.