Three-Dimensional Trajectory Designs for Unmanned Aerial Vehicle-Enabled Communications With Kinematic Constraints

In this paper, we propose novel three-dimensional (3-D) trajectory designs for unmanned aerial vehicle (UAV)-enabled communications, where a single UAV needs to adaptively determine its locations in a timely manner in order to provide radio coverage to terrestrial mobile users. Taking the kinematic constraints on the speed and the turning angle of the UAV into account, we formulate a UAV trajectory optimization problem to maximize the average throughput of the considered system, while satisfying the coverage requirements of the mobile users simultaneously. To solve this NP-hard problem, we first propose an offline trajectory design algorithm that can determine the whole trajectory of the UAV, assuming that the global information (e.g., channel state information and the users' location information at all time slots) is known a priori. Then, we propose two low-complexity online algorithms that utilize the past and current information of the system only. Numerical results are provided to verify the effectiveness of our proposed algorithms. Moreover, we show that our proposed online algorithms can achieve almost the same system performance as the proposed offline algorithm, while inducing significant lower computational complexity.