  Aiding the ground cellular network with aerial base stations carried by
drones has experienced an intensive raise of interest in the past years.
Reconfigurable air-to-ground channels enable aerial stations to enhance users
access links by means of seeking good line-of-sight connectivity while hovering
in the air. In this paper, we propose an analytical framework for the 3D
placement of a fleet of coordinated drone relays. This framework optimizes
network performance in terms of user throughput fairness, expressed through the
{\alpha}-fairness metric. The optimization problem is formulated as a
mixed-integer non-convex program, which is intractable. Hence, we propose an
extremal-optimization-based algorithm, Parallelized Alpha-fair Drone
Deployment, that solves the problem online, in low-degree polynomial time. We
evaluate our proposal by means of numerical simulations over the real topology
of a dense city. We discuss the advantages of integrating drone relay stations
in current networks and test several resource scheduling approaches in both
static and dynamic scenarios, including with progressively larger and denser
crowds.
