  Providing seamless coverage under current cellular network technologies is
surmountable only through gross overengineering. Alternatively, as an
economically effective solution, the use of unmanned aerial vehicles (UAVs),
augmented with the functionalities of terrestrial base stations (BSs), is
recently advocated. In this paper we investigate the effect that the
incorporation of UAV-mounted BSs (U-BS) poses on the coverage probability of
cellular networks. To this end, we focus on the evaluation of the coverage
probability of a large-scale aerialterrestrial heterogenous cellular network
(AT-HetNet), in which BSs of each technology/tier can be either ground (G-BS)
or UBS. Our analysis incorporates the impact of Line-of-Sight (LOS) and non-LOS
(NLOS) path-loss attenuations of both ground-toground (G2G) and Air-to-Ground
(A2G) links. Adopting tools of stochastic geometry we provide an expression for
the coverage probability based on main system parameters and percentage of BSs
in each tier that are aerial. We confirm the accuracy of our analysis. Using
our analysis, we observe that for several common communication environments,
e.g., high-rise and dense urban environments, the inclusion of U-BSs can be
detrimental to the coverage probability. Nevertheless, it is still possible to
minimize the coverage cost by turning off a percentage of G-BSs. Interestingly,
for urban and sub-urban areas one can adjust the altitude of U-BSs in order to
increase the coverage probability.
