  Unmanned aerial vehicle (UAV) is being integrated as an active element in 5G
and beyond networks. Because of its flexibility and mobility, UAV base stations
(UAV-BSs) can be deployed according to the ground user distributions and their
quality of service (QoS) requirement. Although there has been quite some prior
research on the UAV deployment, no work has studied this problem in a 3
dimensional (3D) setting and taken into account the UAV-BS capacity limit and
the quality of service (QoS) requirements of ground users. Therefore, in this
paper, we focus on the problem of deploying UAV-BSs to provide satisfactory
wireless communication services, with the aim to maximize the total number of
covered user equipment (UE) subject to user data rate requirements and UAV-BSs'
capacity limit. First, we model the relationship between the air-to-ground
(A2G) path loss (PL) and the location of UAV-BSs in both horizontal and
vertical dimensions which has not been considered in previous works. Unlike the
conventional UAV deployment problem formulation, the 3D deployment problem is
decoupled into a 2D horizontal placement and altitude determination connected
by path loss requirement and minimization. Then, we propose a novel genetic
algorithm (GA) based 2D placement approach in which UAV-BSs are placed to have
maximum coverage of the users with consideration of data rate distribution.
Finally, numerical and simulation results show that the proposed approach has
enabled a better coverage percentage comparing with other schemes.
