  This paper investigates moving networks of Unmanned Aerial Vehicles (UAVs),
such as drones, as one of the innovative opportunities brought by the 5G. With
a main purpose to extend connectivity and guarantee data rates, the drones
require hovering locations due to limitations such as flight time and coverage
surface. We provide analytic bounds on the requirements in terms of
connectivity extension for vehicular networks served by fixed Enhanced Mobile
BroadBand (eMBB) infrastructure, where both vehicular networks and
infrastructures are modeled using stochastic and fractal geometry as a model
for urban environment. We prove that assuming $n$ mobile nodes (distributed
according to a hyperfractal distribution of dimension $d_F$) and an average of
$\rho$ Next Generation NodeB (gNBs), distributed like an hyperfractal of
dimension $d_r$ if $\rho=n^\theta$ with $\theta>d_r/4$ and letting $n$ tending
to infinity (to reflect megalopolis cities), then the average fraction of
mobile nodes not covered by a gNB tends to zero like
$O\left(n^{-\frac{(d_F-2)}{d_r}(2\theta-\frac{d_r}{2})}\right)$. Interestingly,
we then prove that the average number of drones, needed to connect each mobile
node not covered by gNBs is comparable to the number of isolated mobile nodes.
We complete the characterisation by proving that when $\theta<d_r/4$ the
proportion of covered mobile nodes tends to zero. We provide insights on the
intelligent placement of the "garage of drones", the home location of these
nomadic infrastructure nodes, such as to minimize what we call the
"flight-to-coverage time". We provide a fast procedure to select the relays
that will be garages (and store drones) in order to minimize the number of
garages and minimize the delay. Finally we confirm our analytical results using
simulations carried out in Matlab.
