Research And Implementation Of Encoding And Decoding Technology Of QC-LDPC Codes On MATLAB

With the rapid development of large scale integrated circuit and the rise of moderncoding theory, low-density parity check codes (Low-Density Parity-Check, LDPC Codes)based on near-Shannon limit error correction performance, LDPC code has attracted greatattention in academia of the channel coding area. These days, LDPC codes with its superiorperformance has been widely used in communication systems suca as DVB-S2, CMMB,Wi-Fi and so on.Low-density parity check code is a special linear block codes,it is special in its sparsityon check matrix, which is the root cause of showing a better performance. How to construct apractical good code, how to achieve efficient LDPC code encoding and decoding technologyhave gradually became a hot code theory since the recognition of LDPC codes. LDPC codescan be divided into random LDPC codes and QC-LDPC codes (Quasi-cyclic LDPCquasi-cyclic low-density parity check codes), quasi-cyclic LDPC codes is an importantsubclass of LDPC code.Its biggest feature is the quasi-cyclic structure and the quasic-cycliccodes don’t need to take up a lot of storage space,but simply to store the base matrix.Additionally, its feature of quasi-cyclic makes it easy to achieve efficient low complexityencoding and decoding, easily implemented in hardware.In a word,the research onquasi-cyclic LDPC codes has important theoretical and practical significance.This paper states the basic theoretical knowledge of LDPC codes, analyses the existingmethod for randomization structure and structured construction of LDPC codes, and mainlyintroduces the manner of irregular QC codes which is based on quasi-cyclic structure.LDPCcodes which have the quasi-cyclic double diagonal structure are widely used during the recentyears. The process of its parity check matrix structure, the selection of index matrix parameterdata and method of the girth detection have been studied in this article. Besides, differentencoding methods and complexity were analyzed, the results shows that quasi-cyclic basismatrix construction method can achieve linear complexity encoding. Therefore, the abovemanner can effectively construct a parity check matrix without short girth, can be applied toshort code length LDPC codes. This paper has learned three representative decoding methods, including BP algorithm,the Log-BP algorithm which is based on the logarithmic region and the minimum-sumalgorithms.Combines the above state about method for encoding and matrix structure withdecoding methods, we use the Matlab to simulate the performance. By changing theparameters and the decoding method, the results show that we reach the performancerequirements. So the LDPC codes which have quasi-cyclic double diagonal structure hasdemonstrated its excellent performance.