Abstract-In this paper, the optimal deployment of multiple unmanned aerial vehicles (UAVs) acting as flying base stations is investigated. Considering the downlink scenario, the goal is to minimize the total required transmit power of UAVs while satisfying the users' rate requirements. To this end, the optimal locations of UAVs as well as the cell boundaries of their coverage areas are determined. To find those optimal parameters, the problem is divided into two sub-problems that are solved iteratively. In the first sub-problem, given the cell boundaries corresponding to each UAV, the optimal locations of the UAVs are derived using the facility location framework. In the second sub-problem, the locations of UAVs are assumed to be fixed, and the optimal cell boundaries are obtained using tools from optimal transport theory. The analytical results show that the total required transmit power is significantly reduced by determining the optimal coverage areas for UAVs. These results also show that, moving the UAVs based on users' distribution, and adjusting their altitudes can lead to a minimum power consumption. Finally, it is shown that the proposed deployment approach, can improve the system's power efficiency by a factor of 20× compared to the classical Voronoi cell association technique with fixed UAVs locations. Unmanned aerial vehicles (UAVs) can be used as aerial base stations in order to satisfy the coverage and rate requirements of wireless users [1] and [2] . Due the flying nature of UAVs, they can have line-of-sight (LOS) connections towards ground users thus leading to an improved coverage and rate performance. Compared to terrestrial base stations, mobile UAVs can intelligently move and change their location to provide on-demand coverage for ground users. As a result, UAVbased aerial base stations can be used to boost the wireless capacity and coverage at temporary events or hotspot areas. Effectively deploying UAVs requires meeting key challenges such as air-to-ground channel modeling, optimal deployment, path planning, and energy-efficient operation [3] , [4] . The majority of the literature on UAV communications has mostly focused on empirical and analytical studies on air-to-ground channel modeling [5]- [7] . For example, in [5] , the probability of LOS for air-to-ground communication was derived as a function of the elevation angle for different environments. The path loss model for the air-to-ground channel was further investigated in [6] and [7] . Due to the existence of both path loss and shadowing, the characteristics of the airto-ground channel are shown in [7] to significantly depend on the altitude of the aerial base stations.
The authors in REF utilized the ATG model to find the optimal deployment of UAVs acting as flying base stations to minimize the total required UAV transmit power while satisfying the users' data rate requirements.
Optimal transport theory for power-efficient deployment of unmanned aerial vehicles
2016 IEEE International Conference on Communications (ICC)
2016 IEEE International Conference on Communications (ICC)
Computer Science Mathematics