  In this paper, we provide a performance analysis for practical unmanned
aerial vehicle (UAV)-enabled networks. By considering both line-of-sight (LoS)
and non-line-of-sight (NLoS) transmissions between aerial base stations (BSs)
and ground users, the coverage probability and the area spectral efficiency
(ASE) are derived. Considering that there is no consensus on the path loss
model for studying UAVs in the literature, in this paper, three path loss
models, i.e., high-altitude model, low-altitude model and ultra-low-altitude
model, are investigated and compared. Moreover, the lower bound of the network
performance is obtained assuming that UAVs are hovering randomly according to
homogeneous Poisson point process (HPPP), while the upper bound is derived
assuming that UAVs can instantaneously move to the positions directly overhead
ground users. From our analytical and simulation results for a practical UAV
height of 50 meters, we find that the network performance of the high-altitude
model and the low-altitude model exhibit similar trends, while that of the
ultra-low-altitude model deviates significantly from the above two models. In
addition, the optimal density of UAVs to maximize the coverage probability
performance has also been investigated.
