  Aerial Base Stations (ABSs) have gained significant importance in the next
generation of wireless networks for accommodating mobile ground users and flash
crowds with high convenience and quality. However, to achieve an efficient ABS
network, many factors pertaining to ABS flight, governing laws and information
transmissions must be studied. In this article, multi-drone communications are
studied in three major aspects, survivability, coverage, and mobility laws,
which optimize the multi-tier ABS network to avoid issues related to inter-cell
interference, deficient energy, frequent handovers, and lifetime. The article
includes simulation results of hierarchical ABS allocations for handling a set
of users over a defined geographical area. Several open issues and challenges
are presented to provide deep insights into the ABS network management and its
utility framework.
