Research On Theory And Technology Of Wireless Transmission Based On UAV-Assisted Communications

With the development of communication technology,Unmanned Aerial Vehicle(UAV)-aided communication has gained widespread attention in academia and industry due to their versatility and stable operability.Compared with traditional wireless communications with fixed infrastructure,UAV-assisted wireless communications have considerable advantages,such as using the line of sight(Lo S)communication links to improve the capacity of the wireless communication systems,and using controlled UAV mobility to provide reliable communications.Therefore,the technology of UAV-enabled communication is critical in the future wireless communications and has been widely used.When the UAV carries out data transmission with a ground user,problems such as excessive power consumption,user association,and lower energy efficiency will occur.In view of the above problems,this paper has carried out research on the wireless transmission theory and technology research based on UAV-assisted communication.The specific research contents are as follows:First,the typical air-to-ground channel model is introduced in detail,and the advantages and disadvantages of three common channels,Rayleigh fading channel,Lo S channel and probabilistic Lo S channel,are compared.Then,the free space path loss are introduced in detail.The specific differences between the directional antenna and the omnidirectional antenna are further introduced.Aiming at the problems of interference and association during data transmission between the UAV and the ground user,the Frequency Division Multiple Access(FDMA)technology and the ground user clustering method are introduced in detail.Secondly,in order to solve the problem of downlink power consumption of UAV-assisted wireless communication,a method of optimizing flight altitude and number based on UAV-aided wireless communication is proposed.UAVs serve as mobile flying base stations to serve ground users,and they are equipped with directional antennas with fixed beamwidth.Within a given geographic area,with the ground user's rate requirement as a constraint,based on the principle of ‘total power consumption minimization',the closed-form expressions of the optimal UAV flying altitude and the number of UAVs are derived.The simulation results show that the optimal flying altitude of the UAV depends on the beamwidth of the UAV equipped with a directional antenna,the power of the on-board circuit,and the rate constraint of the ground user.Finally,for the scenario with randomly distributed ground users and different density of ground users in urban and rural areas,a clustering and beamwidth optimization method for UAV-assisted wireless communication is proposed.On the basis of setting the restrictions on the number of users in each cluster,the ground users are divided into several clusters according to their geographic locations,and the UAVs are used to transmit data to the ground users in the cluster,and then based on the principle of ‘energy efficiency maximization',the optimal beamwidth of the directional antenna is derived.The simulation results show that in the scenario where the UAV serves as a mobile aerial base station for the ground users,reasonable clustering ground users and allocating the number of ground users in the cluster can effectively improve the energy efficiency of the air-to-ground wireless communication system.