Energy-efficient optimization for physical layer security in multi-antenna downlink networks with QoS guarantee

In this letter, we consider a multi-antenna downlink network where a secure user (SU) coexists with a passive eavesdropper. There are two design requirements for such a network. First, the information should be transferred in a secret and efficient manner. Second, the quality of service (QoS), i.e. delay sensitivity, should be take into consideration to satisfy the demands of real-time wireless services. In order to fulfill the two requirements, we combine the physical layer security technique based on switched beam beamforming with an energy-efficient power allocation. The problem is formulated as the maximization of the secrecy energy efficiency subject to delay and power constraints. By solving the optimization problem, we derive an energy-efficient power allocation scheme. Numerical results validate the effectiveness of the proposed scheme.