Research And Implementation Of Carrier Synchronization Technology In Digital Communication System

In recent years,with the continuous development of manned spaceflight technology,deep space satellite technology and mobile communication technology,people have increasingly urgent needs for the establishment of communication systems in complex time-varying environments.Existing digital communication technologies all require precise synchronization systems in the receiver.Under the condition of high dynamic communication,since both communicating parties are in high-speed movement,it will cause a great doppler effect or even a high-order rate of change or even sudden channel fading inside the receiver,which seriously affects the signal quality.Reliable reception.This requires a more powerful and efficient carrier synchronization module that can work stably in complex dynamic environments.Therefore,it is of great significance to study the algorithm and concrete realization of carrier synchronization technology in high dynamic environment.The traditional carrier synchronization technology is divided into carrier acquisition technology and carrier tracking technology.Carrier acquisition technology mainly uses the correlation of pseudo-code sequences to search in two dimensions of code phase and carrier frequency.This paper introduces different search techniques based on time domain and frequency domain,and analyzes their theoretical performance and algorithm complexity.Carrier tracking technology mainly uses phase-locked loop technology and Kalman filter technology.This paper introduces the basic structure of the phase-locked loop,and analyzes the basic principle and parameter performance of its basic components.The Kalman filter is a variable-bandwidth loop filter that can be used to replace the phase-locked loop for carrier tracking..This paper introduces the basic principle and process of Kalman filter and the system model applied in carrier tracking,and finally simulates the performance of phaselocked loop,frequency-locked loop and Kalman filter under different parameters.This paper proposes an algorithm based on joint carrier acquisition and carrier tracking under high dynamic conditions.the carrier acquisition algorithm adopts the PMF-FFT algorithm.The PMF-FFT algorithm can complete the carrier synchronization and frequency offset estimation of large frequency offset through partial correlation and FFT,and the coarse step compensation of the frequency offset can reduce the convergence time of the carrier tracking loop.Aiming at the difference of SNR,Viterbi decoding-assisted Kalman carrier tracking algorithm is used under high SNR,and spread spectrum communication scheme is adopted to carry out carrier tracking through the combination of carrier loop and code loop under low SNR.In the carrier tracking scheme of joint decoding,Viterbi decoding can improve the signal-to-noise ratio of the received signal,and carrier tracking by Kalman can greatly improve the robustness of the carrier synchronization module.The low signal-to-noise communication system adopts the extended Kalman method to realize the tracking of the carrier loop,and adopts the delay-locked loop to realize the tracking of the code loop.Finally,combined with the requirements of the project,this paper completes the hardware development and implementation of the carrier synchronization scheme based on FPGA,the hardware implementation of the PMF-FFT carrier acquisition algorithm,the hardware implementation of the Viterbi-assisted phase-locked loop carrier tracking,and the spread spectrum.The hardware implementation of the system carrier tracking,while relying on the upper computer to verify the function,ensures the effectiveness of the communication between the sender and the receiver.