LAUSR

This paper investigates the joint optimization of time allocation and transmit power in wireless-powered communication networks (WPCNs), where the downlink wireless energy transfer happens in the first phase, and then uplink wireless information transfer takes place in the second phase. Considering the rate fairness among users, we formulate the resource allocation in WPCNs as a network utility maximization (NUM) problem that aims to maximize the sum of utilities over all users subject to the energy causality constraint, the quality of service constraint, and the physical constraint. We further prove that the NUM problems with different channel access schemes (the time-division multiple access scheme, the concurrent transmission scheme, and the nonorthogonal multiple access scheme) can be equivalently transformed to convex problems by deliberated math transformations. Simulations demonstrate the efficiency of this paper.