Research On UAV Fleet Based Key Technologies For Emergency Communication Networks

The unforeseen emergencies such as natural disasters caused by the natural variation of the earth’s environment,the large-scale migration of human beings,and the outbreak of social network attacks,have seriously affected people’s production and life order so far.As a critical measure in rapidly acquiring disaster information and rescuing trapped people during emergencies,the construction of Emergency COmmunication NETwork(EcoNet)has always been a concern of governments worldwide.This paper takes frequent natural disasters at home and abroad as primary cases in constructing EcoNet to meet high data flow,differential communication transmission requirements within a specific period under constrained conditions such as limited resources,adverse environments,and damaged infrastructure.The Unmanned Aerial Vehicle(UAV)fleet,with its strong mobility,controllable cost,and flexible deployment,has become an effective way to build EcoNet.Due to the particularity of emergency communication scenarios,there are many problems with traditional UAV-EcoNet,such as difficult representation of shadowing-dominated complex channel model,limited energy supply causing short-endurance,resource allocation problem with various communication mechanisms,and communication island for underground users,and so on.Therefore,a MUlti-tier Heterogeneous UAV Network(MuHun)based EcoNet,which is composed of different task-driven UAVs in different altitudes,is proposed to flexibly serve various emergencies,named Muhun-EcoNet.The penetration communication from on-site command center to trapped users can be realized.To further enhance the system performance of MuHun-EcoNet,advanced Beyond the 5th Generation Mobile Communication/the 6th Generation Mobile Communication(B5G/6G)paradigms are exploited,such as new hybrid-channel model adapted resource allocation,energy-efficient driven Reconfigurable Intelligent Surfaces(RIS)assisted UAV communications,and full-duplex based HETerogeneous NETworks(HetNets)spectrum resource management,to achieve full coverage,high capacity,high energy efficiency and diverse communication services for EcoNet in harsh environments.The main contributions of this dissertation are summarized as follows:1.This paper proposes the architecture of MuHun-EcoNet,which uses multiple costcontrollable UAVs for different altitude platform operations.The MuHun-EcoNet integrates and collaborates the advantages of long-endurance UAVs in medium/high-altitude and flexible takeoff/landing UAVs in low-altitude,to complete communication connection requirements from the on-site command center to the rescue frontline of emergency areas.This can efficiently achieve the tasks of disaster information dissemination and rescue information sharing.Secondly,under the constraints of differential communication environment and limited resources of post-disaster areas,the MuHun-EcoNet enhanced communication scheme is designed.The potential solutions further realize expanded coverage,increased spectral efficiency,and energy efficiency of EcoNet in harsh environments.2.In the paper,we analyze the main channel parameters and characterize the shadowingdominated composite channel caused by collapsed structures and possibly secondary disasters in the complex and changeable communication environment.Then,the characteristics of shadowing-dominated composite channels in single-UAV and multi-UAV scenarios are studied,respectively.Also,the mathematical representation of cascaded F composite channel based on EcoNet complex communication environment is formulated.3.Regarding the limited energy supply of UAV,we propose RIS-assisted UAV communications scheme from the energy efficiency perspective,fully leveraging the advantages of easy-installation and improving communication environment for RIS.Specifically,the optimal power allocation scheme with a single RIS-UAV and the joint bandwidth-power allocation scheme based on multiple RIS-UAV optimization are designed to adapt to the cascaded F composite fading channel.The complex optimization problem is further transformed into gradient iteration algorithm with the help of the supergeometry function operation criteria,thus achieving optimal resource allocation based on the cascade F composite fading channel in EcoNet.In addition,by comparing the energy efficiency of RIS-UAV and traditional relay in EcoNet,the advantage of RIS-UAV in terms of energy efficiency is highlighted.Therefore,RIS-assisted UAV communication can achieve full-angle communication coverage with smaller power consumption in EcoNet,greatly improving the communication connection duration and range in disaster areas.4.For the crowded spectrum caused by differential communication data rate requirements between payload communication links and controllable communication links in MuHunEcoNet,the dynamic spectrum management with HetNets of WiFi-UAV and Cellular network is required.In this paper,we propose the Full-Duplex based Two-Threshold Spectrum Sensing(FDTT-SS)scheme and further Medium Access Control(FDTT-MAC)protocol.Using the proposed FDTT-SS scheme,the LTE-U/WiFi average transmission time can be guaranteed by avoiding collisions among LTE-U/WiFi users.Furthermore,a demandoriented weight factor is used to ensure fair scheduling of HetNets.Numerical results show that the proposed FDTT-MAC protocol can significantly increase the sum throughput without sacrificing the performance of any network.