Research On Carrier Synchronization Technology Of LEO Satellite Based On High Dynamic

In order to satisfy the needs of broadband access in each region,the concept of integration of satellite and ground mobile communication is proposed in the 5G standard.Satellite network is introduced to cover oceans,airspace and remote mountainous areas.LEO satellites have attracted much attention due to their short time delay and large capacity of satellite constellations.In the system of LEO satellite as communication relay station,the terminal and the satellite are in a high dynamic environment due to the large relative velocity and acceleration.In high dynamic environment,the Doppler frequency shift has high-order time-varying characteristics,which makes it more difficult for the receiver to capture and track signal.Therefore,this thesis studies the carrier synchronization technology in LEO satellites with high dynamic environment.In this thesis,carrier synchronization in high dynamic scenarios is divided into two processes,which include carrier frequency acquisition and carrier phase tracking.In terms of carrier frequency acquisition,this thesis proposes two high-precision frequency acquisition algorithms,which are cascaded algorithm and ephemeris assisted algorithm.The cascaded algorithm achieves frequency acquisition in high dynamic scenes by cascading the optimized Discrete Chirp Fourier Transform and the Optimized Pilot Aided Maximum Likelihood algorithm.In addition,in the ephemeris assisted algorithm,the Doppler frequency estimation method with second-order rate of change is deduced based on the Earth Centered fixed coordinate.And then the residual frequency offset is estimated for the signal after compensating for the Doppler frequency shift and rate of change.In terms of carrier phase tracking,this thesis establishes a nonlinear system model of phase,frequency,first-order rate of change and second-order rate of change.And it deduces Extended Kalman Filter and Unscented Kalman Filter algorithm.In the UKF algorithm,aiming at the problem of high probability of lock-out and large jitter in tracking process caused by improper selection of covariance matrix R of observation noise and the scale factor?.This thesis proposes the R-AUKF algorithm.The algorithm achieves the effect of improving tracking accuracy and stability by accurately estimating the covariance matrix R and adaptively selecting the scale factor?.Finally,the carrier synchronization algorithm is simulated in the physical layer simulation platform based on DVB-S2X standard.When E_s/N₀ is-2.8dB,the frequency acquisition probability of cascade algorithm and ephemeris aided algorithm?assuming the ephemeris is accurate?is 90%,and the normalized root mean square error of frequency offset is 1.7×10^-6.The two algorithms have high estimation accuracy.In addition,the performance of carrier phase tracking algorithm is simulated.Compared with traditional EKF algorithm and UKF algorithm,the R-AUKF algorithm has higher tracking accuracy and stability in second-order nonlinear systems.When E_s/N₀ is 3dB,the locking probability is 99%.After the signal is locked,the maximum jitter errors of frequency offset is 14.4Hz.The errors of the first-order rate of change and the second-order rate of change are 4×10^-4Hz/s and 4×10^-5Hz/s².