| Summary: | Communication and networking with unmanned aerial vehicles (UAVs) has attracted increasing attention due to their boundless applications in photography, agriculture, surveillance, and numerous public services. Employing the UAV as a mobile relay is promising to boost the coverage and capacity of the network and shows many advantages over conventional communication networks. In this paper, we investigate joint 3D location and transmit power optimization of the UAV to accommodate the relaying network with multiple mobile users. The objective is to maximize the sum rate of all the mobile users, subjects to the constraints on line-of-sight connectivity for communication links, information-causality constraint, as well as the strict data rate fairness requirement of all users. However, this challenging problem has non-convex objective function, complicated constraints, and strongly coupled variables. To address this problem, we first prove that the optimal solution to the original sum rate maximization problem can be obtained by equivalently solving a more tractable problem. Then, we develop an efficient algorithm by leveraging the alternating descent framework and successive convex approximation method. Next, we show that the proposed algorithm iteratively improves the objective function and is guaranteed to converge within a finite number of iterations. Furthermore, simulation results demonstrate the effectiveness of the proposed algorithm and reveal the impacts of various parameter configurations on the system performance.
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