Research On Carrier Synchronization Technology For Nodes In Wide-area Agility Scenarios

With the development of flying ad hoc networks,short-time burst communication,satellite communication and other theories,there has been increasing attention to the communication between nodes in wide-area agility scenarios.In this scenario,the performance of carrier synchronization between nodes determines the accuracy of demodulation and decoding.However,the implementation of carrier synchronization technology in wide-area agile scenarios is faced with the challenges of low signal-to-noise ratio(SNR),high carrier frequency offset,and short data frame length.In this thesis,the design of carrier synchronization algorithm to improve the range and accuracy of frequency offset estimation with less pilot overhead in the case of low SNR is studied,and frequency offset estimation algorithms for this scenario are proposed.The contributions of this thesis are summarized as follows:In response to the issues that the existing frequency offset estimation algorithm is difficult to guarantee the estimation of range and accuracy at the same time,a high-precision large frequency offset estimation algorithm based on fast fourier transform(FFT)is proposed in this thesis.Firstly,the algorithm estimates the rough carrier frequency offset in frequency domain based on FFT to meet the estimation requirements of large carrier frequency offset.Then the fine estimation of carrier frequency offset based on interpolation is carried out to further improve the accuracy of carrier frequency offset estimation.The algorithm performs well in the case of low SNR because the signal is zeroed in during the process of fine estimation,which is equivalent to reducing the influence of noise.Simulation results show that the proposed algorithm has better estimation accuracy and SNR threshold performance than the existing carrier frequency offset algorithms based on interpolation.In response to the issues of limited data frame length in short-time burst communication systems,a two-step carrier frequency offset estimation algorithm combining data-assisted and non-data-assisted is proposed in this thesis.In the first step,based on general data frame structure,the maximum likelihood theory based frequency offset estimation is carried out by using both pilot sequence and data sequence,which improves the accuracy of frequency offset estimation and reduces the SNR threshold under the limited data frame length.In the second step,the improved time domain estimation algorithm is used to accurately estimate the residual frequency offset after frequency offset compensation for the carrier signal,so as to further improve the overall algorithm performance.Simulation results show that the proposed algorithm has higher estimation accuracy and less pilot cost than the data-assisted algorithm or the non-data-assisted algorithm,which improves the utilization rate of data frames and is suitable for short-time burst communication system.This thesis lays a theoretical foundation for the research of node carrier synchronization in wide-area agility scenarios,and also provides technical support for carrier frequency offset estimation.