Sum-Throughput Maximization with QoS Constraints for Cooperative WPCNs

A wireless powered communication network (WPCN) is considered, which has a hybrid access point (H-AP) and two users with energy harvesting capabilities. The H-AP transfers energy to the users during downlink (DL) transmission, and the users transmit information to the H-AP during uplink (UL) transmission by utilizing the harvested energy. To enhance user fairness, a user cooperation protocol is employed in which a user close to the H-AP relays the message of the other user by partially using its allocated time and available energy resources. By jointly optimizing the time allocation for DL energy transfer and UL information transmission, we maximize the sum-throughput in the considered network subject to a set of quality of service (QoS) requirements. The optimization problem is solved through a divide-and-conquer approach along with convex optimization techniques, and thus an analytical solution is derived. In particular, the conditions under which the WPCN benefits from the user cooperation in achieving the maximum sum-throughput are fully characterized. Furthermore, an efficient resource allocation algorithm to find the optimal solution under QoS requirements is presented.