In this paper, we investigate the secrecy design in a sustainable relay network, where the relay is energy harvesting enabled and utilizes time switching to harvest wireless power. Specifically, assuming half-duplex amplify-and-forward relaying, we investigate the worst-case secrecy rate maximization by jointly designing the relay beamforming matrix, artificial noise covariance, and the time switching ratio. However, the formulated problem is highly non-convex due to the secrecy rate function and the dynamic relay transmit power constraint. By decoupling the original problem, we propose a two-layer optimization algorithm, where the outer problem is solved by two-dimensional search while the inner problem is solved by semi-definite relaxation. Numerical results show the effectiveness of the proposed scheme.
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