  The physical-layer security issue in the multiple non-regenerative
wireless-powered relay (WPR) networks is investigated in this letter, where the
idle relay is treated as a potential eavesdropper. To guarantee secure
communication, the destination-based artificial noise is sent to degrade the
receptions of eavesdroppers, and it also becomes a new source of energy
powering relays to forward the information with power splitting (PS) technique.
We propose an efficient algorithm ground on block-wise penalty function method
to jointly optimize PS ratio and beamforming to maximize the secrecy rate.
Despite the nonconvexity of the considered problem, the proposed algorithm is
numerically efficient and is proved to converge to the local optimal solution.
Simulation results demonstrate that the proposed algorithm outperforms the
benchmark method.
