Research On Synchronization Algorithm In Digital Communication System

With the development of mobile communication and deep space satellite communication technology,people need more and more reliable transmission in complex communication environment.The excellent performance of existing communication algorithm depends on the precise carrier synchronization technology in the digital receiver.The channel environment of low signal to noise ratio(SNR)is very bad,and the traditional carrier synchronization algorithm is difficult to achieve accurate carrier extraction.Even in some cases,it fails completely.Most of the existing coding aided carrier synchronization algorithm has high computational complexity and narrow estimation range,so it is not suitable for practical application.In the high dynamic environment,there is always a large relative motion between the transceiver of the communication system,resulting in a large Doppler frequency offset and high-order change rate of received signal,which seriously exceeds the tracking range of the traditional carrier synchronization technology.This phenomenon will make serious errors in the communication system,and affect the reliable reception of the signal.Therefore,the research of receiver synchronization technology in complex communication environment is of great significance in theory and engineering.The main contents of this paper are summarized as follows.(1)Firstly,this paper introduces the theoretical basis of digital receiver carrier synchronization algorithm,and expounds the communication system model and signal parameters of two complex channel environments in detail;secondly,it summarizes some difficulties faced by receiver carrier synchronization algorithm to achieve high reliable communication in complex communication environment,and focuses on the research of coding aided carrier synchronization algorithm in low SNR environment and carrier synchronization algorithm in high dynamic environment.(2)Secondly,the coding aided carrier synchronization algorithm in low SNR environment is studied.In view of the problems of high computation complexity and narrow estimation range of carrier parameters in the existing synchronization technology,this paper proposes a low complexity and wide range coding aided carrier synchronization algorithm.Firstly,the carrier synchronization algorithm based on M value is used to realize carrier coarse synchronization.In view of the problem that the calculation complexity increases sharply when the accuracy of parameter estimation is high,this paper proposes a low complexity carrier coarse synchronization algorithm based on the hexagon M-value search.It first simplifies the calculation of the cost function,then exhaustively searches with the lower estimation accuracy to find the frequency offset phase offset point corresponding to the maximum value of the M-value function.It searches the cost function corresponding to the six vertices of the hexagon as the center,and compares them to get the best parameters of the coarse estimation.Secondly,we use the carrier synchronization algorithm based on Costas ring to realize carrier fine synchronization,and discretizes the posterior mean according to the reliability of decoding soft information.Theoretical and simulation results show that the proposed code aided carrier synchronization algorithm significantly reduces the computational complexity and improves the estimation range of carrier parameters.(3)The carrier synchronization algorithm in high dynamic environment is studied.In view of the high complexity of the existing synchronization algorithm and the fact that the accuracy of parameter estimation is easy to be affected by other factors,this paper proposes a new acquisition algorithm combining Fr FT and MMSE.First,we use the transformation characteristics of Fr FT to rough estimate the Doppler parameters.Then we use the acquisition algorithm based on MMSE criteria to solve the residual Doppler parameters,which improves the estimation accuracy of the algorithm and reduces the computational complexity of the algorithm.Finally,the third-order phase-locked loop is used to track the residual Doppler frequency offset and the frequency offset rate of change,so as to achieve accurate carrier synchronization in high dynamic environment.On this basis,this paper proposes a carrier synchronization scheme for the low SNR and high dynamic communication environment.Firstly,the pilot sequence is used to quickly capture a wide range of Doppler frequency offset and frequency offset change rate to compensate the received signal.Secondly,the carrier coarse synchronization algorithm based on M-value search is used to estimate and compensate the phase offset in the received signal.Finally,the code aided carrier fine synchronization algorithm based on EKF is used to compensate the residual Doppler frequency offset,frequency offset change rate and phase offset.In this way,precise carrier synchronization can be realized in the low SNR and high dynamic environment.