  We propose a fixed wing unmanned aerial vehicles (UAV)-based millimeter wave
(mmWave) backhaul links, that is offered as a cost effective and easy to deploy
solution, to connect a disaster or remote area to the nearest core network.
First, we fully characterize the single relay fixed-wing UAV-based
communication system by taking into account the effects of realistic physical
parameters, such as the UAV's circular path, critical points of the flight
path, heights and positions of obstacles, flight altitude, tracking error, the
severity of UAV's vibrations, the real 3D antenna pattern, mmWave atmospheric
channel loss, temperature and air pressure. Second, we derive the distribution
of the signal-to-noise ratio (SNR) metric, which is based on the sum of a
series of Dirac delta functions. Using the SNR distribution, we derive
closed-form expressions for the outage probability and the ergodic capacity of
the considered system as a function of all system parameters. To provide an
acceptable quality of service for longer link lengths, we extend the analytical
expressions to a multi-relay system. The accuracy of the closed-form
expressions are verified by Monte-Carlo simulations. Finally, by providing
sufficient simulation results, we investigate the effects of key channel
parameters such as antenna pattern gain and flight path on the performance of
the considered system; and we carefully analyze the relationships between these
parameters in order to maximize the average channel capacity.
