Robust Artificial Noise-Aided Secure Beamforming in Wireless-Powered Non-Regenerative Relay Networks

In this paper, we consider a non-regenerative relay network supporting simultaneous wireless information and power transfer, in which the energy harvesting relay is powered by radio-frequency signals from the source node. Assuming imperfect channel state information from the source/relay to the destination/eavesdropper, we investigate the artificial noise-aided secure robust beamformer that minimize the transmission power at the relay, while guaranteeing the secrecy rate constraint and the transmit power constraint at the relay. In particular, two types of energy harvesting strategies are considered termed power splitting (PS) and time switching (TS), respectively. These constraints make the optimization problems formulated non-convex and challenging, which are efficiently solved by using the S-procedure and semidefinite relaxation techniques to formulate a tractable approximated version of the original problems. Numerical results show the effectiveness of the proposed robust beamforming schemes. Furthermore, the PS strategy performs better than the TS strategy.