Average secrecy rate under transmit antenna selection for the multiple-antenna wiretap channel

This paper presents an investigation of employing transmit antenna selection under secrecy constraints. The transmitter is equipped with multiple antennas while the intended receiver and the eavesdropper have a single antenna each. Instantaneous channel state information of the intended receiver and the eavesdropper are assumed to be available at the transmitter. We derive an analytical expression for the average secrecy rate, in terms of the number of available transmit antennas and the average signal-to-noise ratios at the intended receiver and the eavesdropper. We compare the performance of the antenna selection scheme, as revealed by our analysis, to a precoding scheme based on Generalized Singular Value Decomposition (GSVD) and characterize the loss in the secrecy capacity. In addition, we also derive an expression for the average secrecy capacity for the high SNR regime. From our investigation of the proposed system, we find that the increase of the average secrecy rate with the number of transmit antennas is sub-logarithmic.