Design Of Communication System For Cellular-connected UAVs

The commercialization of 5G cellular networks brings broad development prospects and huge application value to UAVs.After UAVs connect the cellular network,it can achieve a wide range of connection coverage and applications.However,the current cellular network mainly provides services for ground users,and there are still many problems with the access of UAVs to the cellular network.The base station needs a suitable signal coverage model to serve ground users while ensuring the communication quality of aerial drones,interference management strategies for neighboring base stations and ground users,and mobility management of UAVs.In addition,when UAV data is transmitting over the network,it would be affected by network fluctuations,causing problems such as packet loss,sticking,disorder,and failure.This thesis will study the issue of cellular network access and UAV data transmission.Combining cellular access issues and the application requirements for access control,flight control,service deployment,a system framework for Cellular-Connected UAVs is designed.The framework includes three roles: User Equipment,Cellular-Connected UAV and Public Network Server.Then,the communication process between the user and the UAV is formulated,and the functions of the UAV service system were defined.Based on this framework,a Communication System for Cellular-Connected UAVs is implemented,which uses a universal UAV interface and can be easily deployed in various UAVs.To ensure the reliability of UAV data transmission and minimize the communication delay,the UAV’s communication protocol was developed,and the transmission layer protocol and the network device I/O are optimized.And the UAV control program on the User Equipment,the forwarding program on the Public Network Server,and the hardware platform of Cellular-Connected UAV are realized in this system.This system is deployed on a small UAV,and the actual flight test verified its functions.In order to study the problem of UAV access to the cellular network,this thesis also realized a set of Cellular Network Measurement System,which includes a data acquisition UAV equipped with smart phone,a measurement server.Data acquisition program and the corresponding measurement service are implemented in this system.In the suburban environment,the data of cellular network parameters and network performance at different heights is collected.The results of data analysis show that UAVs can only receive weak sidelobe signals at high altitude,resulting in unstable communication and frequent Handover;UDP protocol is more suitable for UAV data transmission,and the network congestion mechanism of TCP protocol will increase transmission time.Therefore,appropriate signal coverage,handover strategies,and network optimization are required for Cellular UAVs.When the cellular network parameters are lower than a certain critical value,the communication failure rate of UAV will increase sharply.This value can be used as a reference for selection of UAV service base station,handover strategy and design of delay sensitive application.