Rank-Two Beamformed Secure Multicasting for Wireless Information and Power Transfer

In this letter, we investigate secure multicasting for simultaneous wireless information and power transfer (SWIPT) in the presence of multiple energy receivers who have potential to eavesdrop on the messages of information receivers. Under both, signal-interference-noise ratio (SINR) and harvested energy constraints, we propose a novel secure multicast design to minimize the total power by using the techniques of rank-two beamformed Alamouti coding and semidefinite relaxation (SDR). The sufficient conditions are derived under which the proposed secure multicast design is optimal. We also present the corresponding rank-two Gaussian randomization procedure to obtain a suboptimal solution when SDR is not tight. Simulation results are then provided to demonstrate the efficacy of the proposed design in power saving.