Secure SWIPT in MISO downlink system with energy efficiency constraint

Energy efficiency (EE) is a key metric in future green wireless networks. In this paper, we study the secure simultaneous wireless information and power transfer (SWIPT) in a downlink multiple-input-single-output (MISO) system, where the energy efficiency (EE) of the system is guaranteed. By jointly designing the transmit beamforming (BF), artificial noise (AN) and power splitting (PS) ratio, the total transmit power is minimized under given quality of service (QoS) and energy harvesting requirement at the legitimate user. To tackle the non-convex problem, we first transform it into a convex one by applying successive convex approximation (SCA), relax the problem into a tractable alternative, and then employ the semi-definite relaxation (SDR) technique. Finally, we use one-dimensional search to obtain the optimal PS ratio. Moreover, the tightness of the relaxation is proved. Simulation results show our proposed algorithm outperforms other schemes such as zero forcing (ZF) or without utilizing AN.