Max-min energy based robust secure beamforming for SWIPT

This paper considers simultaneous wireless information and power transfer (SWIPT) in multiple-input single-output (MISO) downlink systems in which a multi-antenna transmitter sends a secret message to a single-antenna information receiver (IR) and power to multiple single-antenna energy receivers (ERs) in presence of external eavesdroppers. We aim to maximize the harvested energy by the ERs while maintaining the signal-to-interference and noise ratio (SINR) threshold at the IR and keeping the message secure from possible eavesdropping by the malicious attackers by interfering their reception. Both scenarios of perfect and imperfect channel state information (CSI) at the transmitter are studied. Using semidefinite relaxation (SDR) techniques, we show that a rank-one optimal beamforming solution can always be constructed for the IR.