Research On UAV-Enabled Wireless Powered Backscatter Communications

With the development of the fifth-generation(5G)mobile communication technology and the Internet of Things(Io T),a large number of low-power sensors need to be deployed to support various applications,and frequent data exchange will significantly increase the power consumption of the sensors.As an emerging technology,the Wireless Powered Backscatter Communication Network(WPBCN)will play an important role in 5G and Io T networks because of its ability to provide wireless power to low-power sensors.However,the performance of radio frequency-based wireless powered transmission is significantly affected by the high path loss.The transmission efficiency of wireless power will be lower,and so will the communication transmission efficiency.In addition,in remote or under-developed areas,no such power sources may be available for providing radio frequency energy to Io T backscatter devices.In order to enhance the application of wireless powered backscatter communication networks in 5G and Io T networks,the unmanned aerial vehicle(UAV)technique can effectively solve this problem.By exploiting the mobility and flexibility,the UAVs be can deployed in areas where its position can be properly adjusted to reduce the distance to the targeted sensors.Based on this,this dissertation mainly studies two different scenarios to enhance the communication efficiency and power transfer efficiency in the wireless powered backscatter communication network by using the characteri stics of the flexible deployment of UAVs.The main results are summarized as follows:1)We first explore how the deployment position of the UAV will affect the performance of the wireless powered backscatter communication system.Suppose that the communic ation mission duration is sufficiently long,such that the UAV can be viewed as a quasi-static access point(AP).The aim is to maximize the uplink common(minimum)throughput of all ground sensors by optimizing the deployment locations of UAV AP and the allocation of wireless resources under power constraints.The optimal solution shows that for the pure wireless power transfer mode in the downlink,the UAV should successively hover over a limited number of ground positions,and for the uplink backscatter communication mode,the UAV should hover exactly above the sensors.Numerical results show that the proposed quasi-static deployment scheme is superior to the vertical deployment scheme based on ground sensors,and significantly outperforms the single-location hovering scheme based on the sensors’ geometric center.2)Furthermore,a wireless powered backscatter communication network in fully mobile UAV scenario is studied.The aim is to maximize the uplink common(minimum)throughput of all ground sensors by optimizing the UAV trajectory under the UAV’s speed constraint and power constraint.Since the problem is non-convex,we first combine the downlink and uplink radio resource allocation,and propose a successive hovering-and-flying trajectory design.Then,we further propose a local optimal solution to the formulated problem by applying the alternating optimization and Successive Convex Programming(SCP)techniques.Numerical results show that our proposed UAV-enabled WPBCN achieves significant throughput enhancement as compared to the single-point hovering scheme based on the geometric center.Our research will provide a cornerstone for subsequent researchers to explore on UAV-enabled backscatter communication,and provide valuable insights for trajectory optimization and resource allocation in multi-UAV and multi-user WPBCN scenarios.