Research On Time-Frequency Synchronization Design And Algorithm Of New Generation LEO Satellite

The vigorous development of the key technologies of 5G mobile communication has brought a new upsurge of low-orbit satellite.Integrating low-orbit satellite as a supplement into the ecosystem of terrestrial mobile communication has become a new trend of the development of new generation of low-orbit satellite communication.However,due to many objective differences between LEO satellite communication and terrestrial mobile communication,it is necessary to adapt to the differences between satellite and terrestrial communication through various adjustments and improvements in order to find a convergence.One of them is to design the LEO satellite air interface protocol with reference to 5G NR,so that the LEO satellite communication technology can be compatible with 5G to the maximum extent.Time-frequency synchronization is the first step for terminal access to LEO satellite network,and it is also a key technology to support the subsequent continuous communication.Due to the large and time-varying frequency shift in LEO satellite scene,the existing synchronization schemes in terrestrial mobile communication based on 5G can not meet the synchronization requirements of high dynamic satellite scene.This thesis takes satellite-terrestrial integration as the research background,and focuses on the physical layer time-frequency synchronization technology in the new generation of low-orbit satellite mobile communication system.In the research,time-frequency synchronization is divided into initial synchronization phase and synchronization tracking phase.The main research contents and contributions of this thesis are as follows:In the initial synchronization phase,first,the initial synchronization process of 5G LEO satellite is designed based on 5G NR system.Timing synchronization and carrier frequency synchronization are obtained by an algorithm with frequency offset robustness.Then,focusing on the problem that the Doppler shift and crystal frequency offset cannot be distinguished from the carrier frequency offset estimation results,the impact of this problem on the frequency synchronization is analyzed.By designing the terminal crystal frequency offset estimation algorithm,the Doppler shift and crystal frequency offset are separated from the carrier frequency offset during the initial access process,and the frequency offset compensation process of the satellite-ground link is improved.The reliability of the initial synchronization algorithm is verified by simulation of the algorithm in the initial synchronization process,and a high cell ID detection accuracy can be obtained under low signal-to-noise ratio.Through the simulation of the crystal frequency offset estimation algorithm,the superiority of the proposed algorithm in estimation accuracy and frequency stability compared with the traditional algorithm is verified.In the synchronization tracking phase,firstly,a timing synchronization tracking algorithm is designed based on the characteristics of TRS with four subcarriers spaced on the same OFDM symbol.Then,the Doppler rate is introduced to track the time-varying frequency shift.Based on TRS,three algorithms are proposed to estimate the normalized Doppler rate,including TRS-Corr algorithm,LS algorithm and WEIGHTED-LS algorithm.Finally,a link-level simulation platform is built,and compared with the existing algorithms,it is verified that the three algorithms have great superiority over the existing algorithms in the accuracy of frequency offset change rate estimation and frequency offset tracking performance,and the differences in performance and complexity between the three algorithms are analyzed to provide reference for project implementation.