Reaserch On Carrier Synchronization Techology Of High-order APSK Signal

With the rapid development of satellite communications,different satellite systems have an increasing demand for the amount of data transmitted and spectrum resources are becoming more and more tense.Moreover,as the integration of satellite communications and mobile communications systems has gradually become a development trend.The huge data throughput makes the application of high order modulation signals will become more extensive,but the constellation points of high order signals are denser,the Euclidean distance is smaller and they are more sensitive to frequency offset and phase offset,which increases the difficulty of carrier synchronization.The APSK(Amplitude Phase Shift Keying)signal constellation has a circular distribution with fewer amplitude values.Compared with the traditional QAM(Quadrature Amplitude Modulation)modulation,it is more suitable for the nonlinear characteristics of the satellite digital transmission channel,and can improve the spectrum utilization rate at the same time.This thesis mainly focuses on high order APSK signal carrier synchronization technology.The main research of the thesis is as follows:The traditional frequency offset estimation algorithm is analyzed.On this basis,a data-assisted frequency estimation algorithm based on double correlation function is presented.While ensuring the accuracy of the estimation,compared with the L&R algorithm,the estimation range is improved and the complexity is relatively low.Aiming at the problem that it is difficult to track and correct the large frequency offset under the traditional demodulation framework,a frequency offset estimation algorithm based on adaptive acquisition is proposed,which can overcome the problem that the frequency offset causes the spectrum shift of the received signal and affects the subsequent demodulation.Furthermore,a relatively low-complexity correlation algorithm is used for frame synchronization or capturing the start position of burst and the dual-correlation high-precision estimation algorithm is used as an accurate estimation to improve the frequency offset estimation accuracy after adaptive capture.This thesis analyzes the traditional phase offset estimation algorithm and the phase offset estimation algorithm based on the decoupling factor.On this basis,an improved phase decoupling estimation algorithm is given.On the premise that the estimation accuracy is not lost,the phase offset estimation is not affected by the performance of frequency offset estimation.The characteristics of different types of APSK signals are analyzed and the corresponding reduced order transform phase-locking algorithm flow is given for different modulation types.Combining with the frequency and phase offset estimation algorithm proposed in this paper,a high precision joint carrier synchronization estimation algorithm suitable for MAPSK signals is given.It is verified by simulation that it can deal with the problem of poor tolerance of high-order signals to frequency offset.