Synchronization Detection And LDPC Decoding Based On Distributed Frame Synchronization Word

Channel coding is an important part of the communication system,which can effectively enhance the anti-jamming ability of the signal.LDPC code is widely used in the field of modern communication technology because of its good performance.This paper analyzes the decoding process of LDPC codes and finds that the key factor affecting the success of decoding is the accuracy of variable node confidence messages.Therefore,the frame synchronization word and LDPC code can be combined to improve the reliability of variable node messages,so as to achieve fast and accurate decoding.Firstly,through the introduction of the digital communication system model,the important role of channel coding in the communication system is highlighted.The decoding process of LDPC code is simply analyzed,and a LDPC decoding method based on frame synchronization word is proposed.This paper introduces the current research status of LDPC codes and frame synchronization technology at home and abroad,and gives a detailed overview of LDPC codes.It includes the representation of LDPC code,the coding method of Gaussian elimination and the coding method of DVB-S2 standard.Finally,it introduces the LDPC decoding method based on factor graph,including the commonly used BP algorithm and LLR BP algorithm.Secondly,the decoding method of LDPC code based on frame synchronization word is studied.The decoding process of LDPC is analyzed in detail,and the key factor to improve the decoding performance is to improve the confidence of variable node messages.A LDPC decoding method based on distributed frame synchronization words is proposed,and the distribution of frame synchronization words is determined according to the check matrix.Density evolution analysis is carried out for the joint method of frame synchronization word and LDPC code,and Gaussian approximation is used to analyze that this method can reduce the bit error rate of LDPC decoding.The influence of distributed frame synchronization characters on LDPC codes is studied by experimental simulation from many angles.The results show that distributed frame synchronization characters can effectively improve the decoding performance and decoding convergence speed of LDPC codes,but at the same time,it also brings the increase of complexity.Finally,a synchronization detection method for distributed frame synchronization word is proposed.Based on the traditional frame synchronization detection method,the distributed frame synchronization word is extracted according to the local information.The performance of distributed frame synchronization word based on cross correlation detection method and maximum likelihood detection method is analyzed by experimental simulation.The results show that the detection maximum likelihood algorithm based on distributed frame synchronization word is still superior to the correlation detection algorithm.When the number of frame synchronization words is enough,the synchronization accuracy probability can reach100% even when the SNR is much lower than LDPC decoding SNR.