This paper proposes QoS-constrained energy-efficiency (EE) maximization scheme in a multi-antenna wireless powered network. Specifically, considering full CSI at the users, we optimize energy transmit covariance at the power transmitter, the power allocation at the users and the time allocation for energy and information transfer. The EE optimization problem is first converted into its equivalent parameterized subtractive form and, then, the corresponding optimal solution is determined via the Lagrange dual method. The performance of the proposed scheme is validated by simulation.
