  Unmanned aerial vehicles (UAVs)-based applications, such as surveillance
systems and wireless relays, are attracting increasing attention from academia
and industrial fields. The high-performance aerial communication system is one
of the key enablers for them. However, due to the low attenuation of radio
waves in the air-to-ground channels, the interference between aerial and
terrestrial communication systems would significantly deteriorate their
communication performance and greatly limit the potential UAV applications. To
address the problem, in this paper, the spectrum sharing strategy between a
multiple UAV communication system, in which both UAVs and ground station (GS)
are equipped with directional antennas, and terrestrial systems is proposed.
The GS position is selected and the flyable areas of the UAVs using certain
spectrum resources are defined in advance using prior knowledge from spectrum
monitoring on terrestrial communication systems to minimize interference and
maximize the flyable areas of the UAVs instead of the low-efficient dynamic
channel sensing and allocation for interference elimination. The simulations
are conducted through a case study of the spectrum sharing between a multi-UAV
video transmission system and the terrestrial wireless local area network
(WLAN) system in the 5.7GHz band. The simulation results show that thanks to
the proposed system the entire area can be enabled for UAV flight.
