Sum-Rate Maximization Under QoS Constraints for WPCN with User Cooperation

In this paper, we consider a two-user wireless powered communication network (WPCN) with user cooperation, which consists of a hybrid access point (H-AP) and two users with energy harvesting circuit. The H-AP transfers energy to users during downlink (DL) and the users transmit information during uplink (UL) utilizing the harvested energy. To enhance user fairness, a user cooperation protocol is employed in which a user near from the H-AP relays the message of the other user by partially using its allocated time and energy resources. We maximize the sum-rate in the considered network subject to a set of quality of service (QoS) requirements by jointly optimizing the time allocation for DL energy transfer and UL information transmission. A novel closed-form solution is derived for the optimization problem using convex optimization techniques.