Asymptotic Analysis of Average Secrecy Capacity under Transmit Antenna Selection for the MIMO Wiretap Channel

This paper presents an investigation of employing transmit antenna selection for the MIMO wiretap channel. Instantaneous channel state information of the intended receiver and the eavesdropper are assumed to be available at the transmitter. We consider that the eavesdropper employs optimum combining, and investigate the two cases the intended receiver employs (a) optimum combining, (b) sub-optimal combining. We derive analytical expressions of the average secrecy capacities for these two cases in the high-SNR regime. We compare the performance of the proposed antenna selection scheme to a precoding scheme based on generalized singular value decomposition. Our investigations show that the average secrecy capacities increase with the number of antennas when the eavesdropper is at low SNR, but decrease when the eavesdropper is at high SNR.