  UAV enabled communications and networking can enhance wireless connectivity
and support emerging services. However, this would require system-level
understanding to modify and extend the existing terrestrial network
infrastructure. In this paper, we integrate UAVs both as user equipment and
base stations into existing LTE-Advanced heterogeneous network (HetNet) and
provide system-level insights of this three-tier LTE-Advanced air-ground HetNet
(AG-HetNet). This AG-HetNet leverages cell range expansion (CRE), ICIC, 3D
beamforming, and enhanced support for UAVs. Using system-level understanding
and through brute-force technique and heuristics algorithms, we evaluate the
performance of AG-HetNet in terms of fifth percentile spectral efficiency
(5pSE) and coverage probability. We compare 5pSE and coverage probability, when
aerial base-stations (UABS) are deployed on a fixed hexagonal grid and when
their locations are optimized using genetic algorithm (GA) and elitist harmony
search algorithm based on genetic algorithm (eHSGA). Our simulation results
show the heuristic algorithms outperform the brute-force technique and achieve
better peak values of coverage probability and 5pSE. Simulation results also
show that trade-off exists between peak values and computation time when using
heuristic algorithms. Furthermore, the three-tier hierarchical structuring of
FeICIC provides considerably better 5pSE and coverage probability than eICIC.
