  In this paper, we study coverage probabilities of the UAV-assisted cellular
network modeled by 2-dimension (2D) Poisson point process. The cellular user is
assumed to connect to the nearest aerial base station. We derive the explicit
expressions for the downlink coverage probability for the Rayleigh fading
channel. Furthermore, we explore the behavior of performance when taking the
property of air-to-ground channel into consideration. Our analytical and
numerical results show that the coverage probability is affected by UAV height,
pathloss exponent and UAV density. To maximize the coverage probability, the
optimal height and density of UAVs are studied, which could be beneficial for
the UAV deployment design.
