Switched power allocation for MISOME wiretap channels

In this paper, we consider secure communication over a multiple-input single-output Rayleigh-fading channel in the presence of a multiple-antenna eavesdropper - referred to as a multiple-input single-output multiple-eavesdropper (MISOME) wiretap channel. Specifically, secure beamforming with artificial noise is treated when the transmitter has access to full channel state information (CSI) of a legitimate channel but only partial statistical CSI of an eavesdropper channel. We first derive the optimal power allocation between the information-bearing signal and artificial noise (or simulated interference) to maximize the achievable secrecy rate in the presence of a weak or strong eavesdropper. We then develop a near-optimal power allocation strategy in a switched fashion for a general case and derive a closed-form expression for the ergodic secrecy rate achieved by secure beamforming with this switched power allocation in the MISOME wiretap channel.