Robust Cooperative Secure Beamforming for Simultaneous Wireless Information and Power Transfer in Amplify-and-Forward Relay Networks

In this paper, we investigate cooperative secure beamforming for simultaneous wireless information and power transfer (SWIPT) in amplify-and-forward (AF) relay networks. We propose a joint cooperative beamforming (CB) and energy signal (CB-ES) scheme for providing both secure communication and efficient wireless energy transfer. By considering colluding eavesdroppers with imperfect channel state information (CSI), we formulate an optimization problem for maximizing the secrecy rate between the source and the legitimate information receiver (IR) under both the power constraints at the relays and the wireless power transfer constraint at the energy-harvesting receiver (ER). Since such a problem is nonconvex and hard to tackle, we propose a two-level optimization approach that involves a 1-D search and the semidefinite relaxation (SDR) technique to solve this problem. The proposed robust scheme is compared with some other nonrobust schemes, such as a CB and artificial noise (CB-AN) scheme and a perfect scheme. Simulation results show that the proposed robust scheme achieves better worst-case secrecy rate performance than the other nonrobust schemes and the CB-AN scheme, while it approaches the perfect scheme.