Performance Analysis Of NOMA Transmission In UAV Assisted Satellite Communication Systems

Due to its extensive coverage and lack of topographical limits,satellite communication has overtaken ground communication as one of the essential technologies for the next generation of mobile communication systems.Then,unmanned aerial vehicle(UAV)communication has the benefits of simple deployment,control and flexible networking.The received signal power,system capacity,and communication reach can all be improved by using UAV as an air relay to help satellite and ground users connect.This thesis analyzes the non-orthogonal multiple access(NOMA)transmission performance of UAV-assisted satellite communication systems with a focus on various common scenarios,so as to provide reference and basis for system design.The primary contributions of the thesis are provided as follows:1.For the multi-user satellite communication scenario using NOMA-ALOHA scheme,the system throughput is analyzed taking into account the different probabilities of users accessing different power levels.Firstly,the throughput lower bound expression of the multi-user satellite communication system is obtained,assuming that the ground user-UAV link obeys the Nakagami-m distribution and the satellite-UAV link obeys the shadow Rice distribution.Then,the user’s average transmitted power upper bound expression is computed,taking into account the fact that the user can select the subchannel and power level in accordance with the channel gain.Finally,the computer simulation results verify the validity of the proposed scheme and the theoretical formulas,and analyze the influence of subchannel number,threshold,and other relevant factors on system performance.2.For the uplink of UVA-assisted satellite communication system,the NOMA transmission performance of multi-user system based on time division multiplexing access(TDMA)is studied.Firstly,in case that UAV equipped multi-antenna serves as a relay station to aid satellite communication,and the expressions of user output signal-to-interferrnce-and-noise ratio are obtained in two cases using successive interference cancellation(SIC)and joint coding(JD)technology.Then,considering that the ground users-UAV links undergo Nakagani-m fading and the UAV-satellite links undergo shadow Rice fading,the closed expressions of system outage probability using SIC and JD technology are derived respectively.Furthermore,the throughput expression of the system is obtained.Finally,numerical results verify the validity of the theoretical analysis,and compare the system performance with SIC and JD technology,the influence of related parameters on the system performance is analyzed.3.For the downlink of UVA-assisted satellite communication system,the NOMA transmission performance of multi-user system based on space division multiple access(SDMA)is studied.Firstly,in case that UAV employs multi-antenna ans NOMA technique to serve multiple users,the user output signal-to-noise ratio expression under Amplify-and-Forward(AF)protocol was obtained.Then,an optimization problem based on the average signal-to-interferrnce-and-noise ratio maximization is obtained,and a beamforming scheme based on angle information is proposed.Secondly,considering that the satellite-UAV links undergo the correlation shadow rice fading and the UAV-ground user links undergo the Nakagami-m fading,the closed expression of the system outage probability and the throughput expression of the system are derived.Finally,the simulation results verify the validity of the theoretical formulas and the superiority of the proposed scheme.