  In this study, we consider an unmanned aerial vehicle (UAV)-assisted
heterogeneous network that is offered as a cost-effective and easy to deploy
solution to solve the problem related to transferring traffic of distributed
small cells to the core network. For any given distribution of small cell base
stations (SBSs), we first characterize an accurate millimeter wave (mmWave)
channel model for SBS to networked flying platform (NFP) by taking into
consideration real parameters such as UAV's vibrations, distribution of SBSs,
position of UAVs in the sky, real three-dimensional (3D) antenna pattern model
provided by 3GPP along with interference caused by antenna side lobes and
frequency reuse. Then, for the characterized channel, we derive an analytical
closed-form expression for the end-to-end signal-to-noise plus interference
ratio (SINR). Based on that, we derive the closed-form expressions for the
outage probability and channel capacity of the considered UAV-based mmWave
uplinks. The accuracy of the derived analytical expressions is verified by
Monte Carlo simulations. Finally, we investigate the effects of different
channel parameters such as antenna pattern gain, strength of UAV's vibrations,
UAVs' positions in the sky, distribution of SBSs, and frequency reuse on the
performance of the considered UAV-based uplink channel in terms of average
capacity and outage probability.
