Stochastic Optimal Control for Wireless Powered Communication Networks

In this paper, we propose a stochastic optimal control algorithm for the wireless powered communication networks (WPCNs), in which the access point (AP) supplies energy to wireless nodes by means of the RF energy transfer technology. The energy beamforming is used to enhance the RF energy transfer efficiency by concentrating the radiated power on target nodes. Each wireless node is equipped with an energy queue and a data queue. We propose an algorithm that minimizes the expected energy transmission power from the AP while stabilizing the data queues of all nodes. The proposed algorithm is an online algorithm that adaptively decides the beamforming vector, the data scheduling, and the data transmission power, only based on the current state of the energy and the data queues. The proposed algorithm dynamically steers the energy beam to nodes that currently have low energy in the energy queue. We apply the Lyapunov optimization technique to design such an algorithm. We mathematically prove that the proposed algorithm achieves the optimal performance.