Energy-Efficient UAV Deployment with Flexible Functional Split Selection

In this paper, we consider the deployment of unmanned aerial vehicles (UAVs) along a straight road, and aim to minimize the total energy consumption of UAVs, including the baseband processing energy, the wireless fronthauling energy and the constant circuit energy. Specifically, the horizontal location, vertical location, coverage radius and the functional split scheme selection of UAVs are jointly optimized. Both the user data rate and the total delay consisting of baseband processing and fronthaul transmission are guaranteed. To reduce the optimization complexity, we further derive the upper and lower bounds of the optimal number of UAVs. Numerical results show that, with flexible functional split, the energy consumption of UAVs can be considerably reduced compared with fixed functional split. We also observe that more baseband functions should be placed at the UAV side when the distance between the UAV and the baseband units (BBU) on the ground is larger.