  In this paper, we consider a heterogeneous repository of drone-enabled aerial
base stations with varying transmit powers that provide downlink wireless
coverage for ground users. One particular challenge is optimal selection and
deployment of a subset of available drone base stations (DBSs) to satisfy the
downlink data rate requirements while minimizing the overall power consumption.
In order to address this challenge, we formulate an optimization problem to
select the best subset of available DBSs so as to guarantee wireless coverage
with some acceptable transmission rate in the downlink path. In addition to the
selection of DBSs, we determine their 3D position so as to minimize their
overall power consumption. Moreover, assuming that the DBSs operate in the same
frequency band, we develop a novel and computationally efficient beamforming
method to alleviate the inter-cell interference impact on the downlink. We
propose a Kalai-Smorodinsky bargaining solution to determine the optimal
beamforming strategy in the downlink path to compensate for the impairment
caused by the interference. Simulation results demonstrate the effectiveness of
the proposed solution and provide valuable insights into the performance of the
heterogeneous drone-based small cell networks.
