  Service providers are considering the use of unmanned aerial vehicles (UAVs)
to enhance wireless connectivity of cellular networks. To provide connectivity,
UAVs have to be backhauled through terrestrial base stations (BSs) to the core
network. In particular, we consider millimeter-wave (mmWave) backhauling in the
downlink of a hybrid aerial-terrestrial network, where the backhaul links are
subject to beamforming misalignment errors. In the proposed model, the user
equipment (UE) can connect to either a ground BS or a UAV, where we
differentiate between two transmission schemes according to the backhaul
status. In one scheme, the UEs are served by the UAVs regardless of whether the
backhaul links are good or not. In the other scheme, the UAVs are aware of the
backhaul links status, and hence, only the subset of successfully backhauled
UAVs can serve the UEs. Using stochastic geometry, the performance of the
proposed model is assessed in terms of coverage probability and validated
against Monte-Carlo simulations. Several insights are provided for determining
some system parameters including the UAVs altitude and required number and the
beamforming misalignment error of the backhaul link. The obtained results
highlight the impact of the UAVs backhaul link on the UE experience.
