  This paper studies the feasibility of supporting drone operations using
existent cellular infrastructure. We propose an analytical framework that
includes the effects of base station (BS) height and antenna radiation pattern,
drone antenna directivity and various propagation environments. With this
framework, we derive an exact expression for the coverage probability of ground
and drone users through a practical cell association strategy. Our results show
that a carefully designed network can control the radiated interference that is
received by the drones, and therefore guarantees a satisfactory quality of
service. Moreover, as the network density grows the increasing level of
interference can be partially managed by lowering the drone flying altitude.
However, even at optimal conditions the drone coverage performance converges to
zero considerably fast, suggesting that ultra-dense networks might be poor
candidates for serving aerial users.
