| With the advantages of low cost,high mobility,and ease of deployment,unmanned aerial vehicles(UAVs)have played an increasingly important role in the field of wireless communications or data collection as mobile air base stations/auxiliary relays in recent years.In the future,it is expected that the use of UAVs in wireless communication will be more extensive.In this paper,we focus on the path planning in the UAV mobile relay system,and aim to improve the communication performance of the UAV mobile relay system and provide users with a better communication experience.Firstly,we introduce the development trend of current UAVs and the main applications of UAVs and analyze the research significance of UAV mobile relay systems.The main research directions of the UAV relay system are analyzed,and some problems existing in the current research are pointed out,which indicates the necessity of UAV auxiliary relay research.Furthermore,we introduce the theoretical basis,channel model,resource allocation,and performance evaluation indicators of the UAV relay system.Then,we study the path planning problem in inefficient three-node UAV mobile relay system and propose an elliptical path planning mobile model to maximize spectrum efficiency.The mobile model we proposed breaks the existing pattern based on specific mobile models such as circles or straight lines.By jointly optimizing the time allocation and elliptical trajectory,the spectrum efficiency is maximized.Then we compare the communication performance of the elliptical path planning method with the static relay and circular path planning methods,and the simulation results show that the elliptical path planning method proposed in this paper can improve the system’s spectrum efficiency.Finally,we investigate the path planning problem in energy-constrained multi-node relay sensor network.And an information receiving strategy based on the combination of fly-receiving mode and hover-receiving mode was proposed to minimize the information transmission delay.We divide the UAV path planning problem in a multi-node network into multiple single-node UAV path planning sub-problems at first.Then we jointly optimize the optimal power allocation,the speed of the UAV and the best receiving position in the case of a single node.And the problem of minimizing the delay of multi-node information is transformed into the minimum path planning problem with time weight,and the relay sequence of the multi-node relay system is determined.We then compared the information delay in hover-receiving mode,fly-receiving mode and the combined mode.and the simulation results show that the combination of the two mode can reduce the information delay of all nodes and improve the communication of the system performance. |
