  This paper investigates a full-duplex orthogonal-frequency-division multiple
access (OFDMA) based multiple unmanned aerial vehicles (UAVs)-enabled
wireless-powered Internet-of-Things (IoT) networks. In this paper, a swarm of
UAVs is first deployed in three dimensions (3D) to simultaneously charge all
devices, i.e., a downlink (DL) charging period, and then flies to new locations
within this area to collect information from scheduled devices in several
epochs via OFDMA due to potential limited number of channels available in
Narrow Band IoT, i.e., an uplink (UL) communication period. To maximize the UL
throughput of IoT devices, we jointly optimizes the UL-and-DL 3D deployment of
the UAV swarm, including the device-UAV association, the scheduling order, and
the UL-DL time allocation. In particular, the DL energy harvesting (EH)
threshold of devices and the UL signal decoding threshold of UAVs are taken
into consideration when studying the problem. Besides, both line-of-sight (LoS)
and non-line-of-sight (NLoS) channel models are studied depending on the
position of sensors and UAVs. The influence of the potential limited channels
issue in NB-IoT is also considered by studying the IoT scheduling policy. Two
scheduling policies, a near-first (NF) policy and a far-first (FF) policy, are
studied. It is shown that the NF scheme outperforms FF scheme in terms of sum
throughput maximization; whereas FF scheme outperforms NF scheme in terms of
system fairness.
