Signal and artificial noise beamforming for secure simultaneous wireless information and power transfer multiple‐input multiple‐output relaying systems

Simultaneous wireless information and power transfer (SWIPT) is a potential technique to solve the energy scarcity problem in wireless communication networks. Information transmission security is one of the key issues to be addressed in SWIPT. In this study, the authors consider guaranteeing the information transmission security of a multiple‐input multiple‐output non‐regenerative relay system with SWIPT in the physical layer by designing source and relay beamforming to maximise the security rate of the system. The problem is to design the source signal and artificial noise (AN) beamforming and the relay forwarding beamforming jointly, which is highly non‐convex. They first propose an alternating optimisation‐based algorithm, which designs the beamforming matrices at the source and relay separately and alternately. Next, they propose a joint design algorithm which designs the source signal and AN beamforming and the relay beamforming together. Finally, they propose a non‐iterative design algorithm with low complexity. The performances of the proposed design algorithms have been verified by computer simulations.