Cooperative Beamforming for Antieavesdropping Communications Systems

Abstract

This article introduces an antieavesdropping method named cooperative beamforming that simultaneously exploits the benefits of multiple-input multiple-output and coordinated multiple-point communications. Specifically, to enhance the security of the user terminal (UT), we propose to employ multiple multiantenna base stations to cooperatively form beams that intersect at a small area, where messages can only be well received. In particular, the original message intended for the UT is divided into submessages, each of which will be transmitted by different base stations. A counterintuitive phenomenon is discovered that the crossing point of beams is not the achievable rate highest point from the perspective of antieavesdropping communications. Correspondingly, an optimization problem is formulated to find beam azimuths and select proper serving base stations for maximizing the achievable rate under the security constraint. A Nelder–Mead-based algorithm is developed to optimize beam azimuths for maximizing the achievable rate of the UT for a given group of selected serving base stations. To address the mixed-integer nonlinear programming problem in selecting serving base stations, we further develop a low-complexity algorithm. Simulation results show that the performance of the proposed algorithm is near to the exhaustive search, which validates the effectiveness of the proposed antieavesdropping method.