  The integration of unmanned aerial vehicles (UAVs) into wireless networks has
opened a new horizon to meet the capacity and coverage requirements foreseen in
future wireless networks. Harnessing UAVs as flying base stations (BSs) has
helped to achieve a cost-effective and on-the-go wireless network that may be
used in several scenarios such as to support disaster response and in temporary
hotspots. Despite the extensive research on the application side of UAVs, the
integration of UAVs as BSs into existing wireless networks remains an open
challenge. While UAV BSs can help to increase the area spectral efficiency, the
added network heterogeneity and BS densification may diminish the capacity
gains due to increased handover rates. In this work, we shed some light on this
tradeoff by studying a three tier network architecture consisting of macro,
small, and UAV BSs and analyze its coverage and rate performance. In
particular, we consider joint control/data and split architectures and express
the rate performance for stationary and mobile users, using an analytical
approach based on stochastic geometry. While both joint and split architectures
offer similar performance for stationary users, the numerical results suggest
the splitting of control and data plane for mobile users.
