Research On Synchronization Of LEO Satellite LTE Communication System

Low-orbit satellite communication system can achieve global seamless coverage,it solves the problem of blind coverage in the ground network or dilutes the users' densities area of the basic communication problems.while in natural disasters or hot spots,it can be a backup and supplement on the ground communication network.As the starting point of cellular technology,the ground mobile communication has been developed rapidly in recent years.In order to achieve a higher data rate,3GPP proposed OFDMA and MIMO technology,LTE communication protocol was proposed after many years of research.With the development of LTE communication technology,the application of LTE communication technology to low-orbit satellite communication system has become a new research direction.In this thesis,the application of LTE protocol in low-orbit satellite communication system is analysed,and a low-orbit satellite channel model is proposed after analysing the characteristics of satellite channel.The key technologies of LTE communication protocol are used to build and improve the uplink system for low-orbit satellites.The simulation analysis of this thesis is mostly based on the satellite uplink system.Firstly,this thesis analyses the process of LTE uplink random access and synchronization.This thesis analyses and puts forward some problems when LTE standard applies to low-orbit satellite scene.This thesis designs a new preamble sequence to adapt to the problem of long delay in the low-orbit satellite environment,and verifies the new preamble sequence structure's detection performance in the satellite link system by simulation.When the LTE system is applied to the low orbit satellite,the the large Doppler frequency shift will cause frequency synchronization problem.This thesis studies the estimation algorithm of frequency offset and improves the estimation algorithm of integer frequency deviation based on the application of low orbit satellites.At the same time,the estimation performance is verified by simulation.Finally,this thesis analyses the problem of timing TA in traditional terrestrial LTE system,and proposes TA mechanism to adapt to the large delay scene of LEO satellite.At the same time,aiming at the existence of timing error in the transmitter and receiver side of the satellite link,This thesis uses the existing time offset estimation algorithm to compensate and improves the existing algorithm.The estimation performance of the algorithm is verified by simulation.The estimation and compensation of satellite timing offset improves the communication performance of the link system.