Synchronization On Low Orbit Satellite Mobile Communication System Based On 5G Protocal Standard

Satellite mobile communication systems have the characteristics of wide coverage,flexible networking and do not influenced by natural disasters.It has become an important part of the future global communications network.The 5G NR also defines a non-terrestrial network access technology for satellite systems.Construct a broadband satellite mobile communication system using key technologies on terrestrial 5G mobile communication systems is of great significance.This article aims at low-orbit satellite systems and studies the synchronization technology of 5G-based broadband satellite mobile communication systems.First,the channel modeling of low-orbit satellite mobile communication system is studied.In view of the transmission scenarios of low-orbit satellite mobile communication systems,the fading characteristics of low-orbit satellite mobile communication transmission channels is introduced,and the corresponding channel model is given.Subsequently,the timing synchronization and frequency synchronization methods in satellite mobile communication systems are studied.The influence of timing and frequency deviation on system performance is analyzed.Combining the orbit and beam information of low-orbit satellites,a frequency offset pre-correction method based on the beam top-view angle are proposed.The Doppler frequency offsets were quickly estimated and real-time compensated with lower computational complexity,and the frequency offset is controlled in a relatively small range.Then,the frequency synchronization algorithm in LEO satellite mobile communication system is studied.Aiming at solving the problem of large Doppler frequency offset in low-orbit satellite mobile communication system,giving a method of time-domain segmented crosscorrelation.By increasing the value of segment correlation,the estimation range of frequency offset gradually increases,but with the increase of the number of segments the frequency offset estimation range do not increase linearly,so this algorithm is suitable for estimating the case where the Doppler frequency offset value is small.In order to solve the abovementioned problem,a method of estimating the integer frequency offset and the fractional frequency offset are separately proposed.An improved segment correlation method are proposed for fractional frequency estimation and symbol timing synchronization.Its performance does not affected by integer frequency offset.For the integer frequency offset estimation,frequency domain crosscorrelation method and zero-pilot sequence method are given.Simulation results show that the proposed method can effectively solve the large frequency offset estimation problem in loworbit satellite mobile communication systems.Finally,the problem of symbol timing synchronization in satellite mobile communication systems is studied.Firstly,a symbol synchronization algorithm based on cyclic prefix is proposed,and CP is used to completed symbol timing synchronization and fractional frequency offset estimation.The algorithm performance does not affected by large frequency offset.Therefore,it can be used as a symbol timing synchronization method in a large-frequency offset scene of a low-orbit satellite communication system.