  In this paper, we consider an Unmanned Aerial Vehicle (UAV)-assisted cellular
system which consists of multiple UAV base stations (BSs) cooperating the
terrestrial BSs. In such a heterogeneous network, for cellular operators, the
problem is how to determine the appropriate number, locations, and altitudes of
UAV-BSs to improve the system sumrate as well as satisfy the demands of
arbitrarily flash crowds on data rates. We propose a data-driven 3D placement
of UAV-BSs for providing an effective placement result with a feasible
computational cost. The proposed algorithm searches for the appropriate number,
location, coverage, and altitude of each UAV-BS in the serving area with the
maximized system sumrate in polynomial time so as to guarantee the minimum data
rate requirement of UE. The simulation results show that the proposed approach
can improve system sumrate in comparison with the case without UAV-BSs.
