  In emergency scenarios, unmanned aerial vehicles (UAVs) can be deployed to
assist localization and communication services for ground terminals. In this
paper, we propose a new integrated air-ground networking paradigm that uses
dual-functional UAVs to assist the ground networks for improving both
communication and localization performance. We investigate the optimization
problem of deploying the minimal number of UAVs to satisfy the communication
and localization requirements of ground users. The problem has several
technical difficulties including the cardinality minimization, the
non-convexity of localization performance metric regarding UAV location, and
the association between user and communication terminal. To tackle the
difficulties, we adopt D-optimality as the localization performance metric, and
derive the geometric characteristics of the feasible UAV hovering regions in 2D
and 3D based on accurate approximation values. We solve the simplified 2D
projection deployment problem by transforming the problem into a minimum
hitting set problem, and propose a low-complexity algorithm to solve it.
Through numerical simulations, we compare our proposed algorithm with benchmark
methods. The number of UAVs required by the proposed algorithm is close to the
optimal solution, while other benchmark methods require much more UAVs to
accomplish the same task.
