  This paper investigates a wireless powered communication network (WPCN) under
the protocol of harvest-then-transmit,where a hybrid access point with constant
power supply replenishes the passive user nodes by wireless power transfer in
the downlink,then each user node transmit independent information to the hybrid
AP in a time division multiple access (TDMA) scheme in the uplink.The
sum-throughput maximization and min-throughput maximization problems are
considered in this paper.The optimal time allocation for the sum-throughput
maximization is proposed based on the Jensen's inequality,which provides more
insight into the design of WPCNs.A low-complexity fixed-point iteration
algorithm for the min-throughput maximization problem,which promises a much
better computation complexity than the state-of-the-art algorithm.Simulation
results confirm the effectiveness of the proposed algorithm.
