Multiple-UAV-Assisted SWIPT in Internet of Things: User Association and Power Allocation

Simultaneous wireless information and power transfer (SWIPT) has sparked a wave of interest in research, while unmanned aerial vehicles (UAVs) can offer a high level of service for Internet of Things (IoT) due to its deployment flexibly. In this paper, we employ multiple UAVs as transmitters to realize information-transmitting and energy-transferring for ground IoT devices simultaneously to expand the capacity and coverage of the network, where each UAV is associated with multiple ground devices. This paper investigates joint optimization of three-dimensional (3D) locations, user association and power allocation of the UAVs with the aim of maximizing the minimum data rate among multiple dispersed users on the ground while guaranteeing the energy requirement of each user. Meanwhile, the proposed optimization problem contains the transmit power budget of each UAV and constraints on user association. The feasibility analysis ensures that the problem can be solvable. To address the combinatorial optimization problem, non-convex problems are decomposed into two subproblems. Then they are transformed into a series of convex problems alternately via successive convex optimization technique. Subsequently, we develop a multivariable iterative algorithm to settle the overall problem. Next, the convergence performance of the proposed algorithm is confirmed. In conclusion, simulation results operated under various parameter configurations substantiate the proposed algorithm can achieve a higher data rate compared with other benchmark schemes.