  Unmanned Aerial Vehicles (UAVs) have been extensively utilized to provide
wireless connectivity in rural and under-developed areas, enhance network
capacity and provide support for peaks or unexpected surges in user demand,
mainly due to their fast deployment, cost-efficiency and superior communication
performance resulting from Line of Sight (LoS)-dominated wireless channels. In
order to exploit the benefits of UAVs as base stations or relays in a mobile
network, a major challenge is to determine the optimal UAV placement and
relocation strategy with respect to the mobility and traffic patterns of the
ground network nodes. Moreover, considering that the UAVs form a multi-hop
aerial network, capacity and connectivity constraints have significant impacts
on the end-to-end network performance. To this end, we formulate the joint UAV
placement and routing problem as a Mixed Integer Linear Program (MILP) and
propose an approximation that leads to a LP rounding algorithm and achieves a
balance between time-complexity and optimality.
