Research Of Carrier Synchronization In Low SNR And High Dynamic Environment

In recent years, with the development of the mobile satellite communication andsatellite navigation system, low signal-to-noise ratio(SNR) and high dynamic environmentof satellite communication is becoming more and more attention. In low SNR and highdynamic environment, large Doppler frequency offset and its rate are produced betweenboth sides of communication due to relative motion velocity and acceleration. And as aresult of the limitation of transmission power and the antenna gain, low SNR is betweentwo sides of communication. This article studied carrier synchronization technology in lowSNR and high dynamic environment.The carrier synchronization is divided into two processes which is acquisition andtracking. Acquisition provides prior knowledge for tracking process to lock tracking loopquickly. In order to capture high dynamic signals in low SNR environment, this paperproposes two acquisition methods, the first is based on two-level frequency rateapproximation in the frequency domain, another is based on CAPON and dimensionreduction. The computation load of the first method is less, but this method has errortransfer effect leading to the low estimation accuracy; The high estimation accuracy of thesecond method is at the cost of large computation load. Meanwhile, this paper compares thetwo order frequency-locked loop aiding three order phase-locked loop to the carriertracking algorithm based on Extended Kalman Filter (EKF). MATLAB simulation resultsshow the two order frequency-locked loop aiding three order phase-locked loop can notlock in low SNR, while the EKF loop has stable tracking performance in high dynamic andlow SNR environment.WhenEs N06dB, Doppler frequency offset is48kHz and its rate is2802Hz/s,we carry out simulation on pure carrier. The simulation results show the two-levelfrequency rate approximation method can limit Doppler offset under1.5Hz and frequencyrate under10Hz s; And the EKF loop tracking performance is stable, whose lockprobability can reach ninety-nine percent if acquisition provides prior knowledge totracking loop.Finally, this paper introduces the implementation method of two-level frequency rateapproximation using VHDL hardware description language in ISE developmentenvironment, which passes Modelsim function simulation and the on-board debugging.