  This paper aims to propose a three-dimensional (3D) point process that can be
employed to generally deploy unmanned aerial vehicles (UAVs) in a large-scale
cellular network and tractably analyze the fundamental network-wide
performances of the network. This 3D point process is devised based on a 2D
marked Poisson point process in which each point and its random mark uniquely
correspond to the projection and the altitude of each point in the 3D point
process, respectively. We elaborate on some important statistical properties of
the proposed 3D point process and use them to tractably analyze the coverage
performances of a UAV-enabled cellular network wherein all the UAVs equipped
with multiple antennas are served as aerial base stations. The downlink
coverage of the UAV-enabled cellular network is found and its closed-form
results for some special cases are explicitly derived as well. Furthermore, the
fundamental limits achieved by cell-free massive antenna array are
characterized when coordinating all the UAVs to jointly perform non-coherent
downlink transmission. These findings are validated by numerical simulation.
