Max-min energy-efficiency optimization in wireless powered communication network with harvest-then-transmit protocol

In this paper, we propose an energy-efficient transmission scheme for wireless powered communication networks with harvest-then-transmit protocol. Specifically, considering fairness among users, we present time resource allocation scheme to maximize the individual energy efficiency(EE) of each user, defined as a ratio of the user throughput to its harvested energy,based on the max-min criterion. EE optimization problem is highly non-convex and difficult to directly tackle. To solve this difficulty, we initially convert two EE problem into its equivalent parameterized subtractive form and, then, the corresponding optimal solution is determined via efficient two-layer iterative algorithm. The simulation results show that the proposed scheme provides better EE performances than those of the conventional schemes and the fairness-based algorithm considerably outperforms the other schemes in terms of the minimum user EE.