Throughput Maximization in Wireless Powered Communication Networks with Energy Saving

Abstract—This paper considers a time division multiple access scenario where a wireless access point transmits to a group of users which harvest the energy and then use this energy to transmit back to the access point. Past approaches have found the optimal time allocation to maximize sum throughput under the assumption that the users must use all of their harvested power in each block of the “harvest-then-transmit ” protocol. This paper considers optimal time and energy allocation to maximize the sum throughput for the case when the nodes can save energy for later blocks. To maximize the sum throughput over a finite horizon, the initial optimization problem is separated into two sub-problems and finally can be formulated into a standard box-constrained optimization problem, which can be solved efficiently. A tight upper bound is derived by relaxing the energy harvesting causality. Simulation results are also provided to demonstrate the “harvest-then-transmit ” protocol with energy saving provides improved sum throughput increasing with the number of transmission blocks. Index Terms—wireless power transfer, energy harvesting, sum throughput maximization I