  The ability to operate anywhere, anytime, as well as their capability to
hover and carry cargo on board make Unmanned Aerial Vehicles (UAVs) suitable
platforms to act as Flying Gateways (FGWs) to the Internet. The problem is the
optimal placement of the FGWs within the flying network, such that the Quality
of Service (QoS) offered is maximized. The literature has been focused on
optimizing the placement of the Flying Access Points (FAPs), which establish
high-capacity small cells to serve the users on the ground, overlooking the
backhaul network design, including the FGW placement. The FGW placement problem
is exacerbated in highly dynamic flying networks, where the dynamic traffic
demand and the movements of the users may induce frequent changes in the
placement of the FAPs.
  The main contribution of this paper is a fast gateway placement (F-GWP)
algorithm for flying networks that determines the optimal position of a FGW.
With F-GWP, backhaul communications paths with high enough capacity are
established between the FAPs and the FGW, in order to accommodate the traffic
demand of the users on the ground. Simulation and experimental results show
F-GWP is two orders of magnitude faster than its state of the art counterpart,
while ensuring the same flying network performance.
