Research On The Construction Algorithm Of Quasi-Cyclic LDPC

LDPC code is recognized as one of the best channel coding now, it can be used on almost all the channel and the structure of its check matrix is very simple, with approaching shannon limit of error correction performance. In the actual implementation, the realization of the decoder is simple and the rsources can be saved with the parallel operation. Quasi-cyclic LDPC code is a kind of structured LDPC code, with quasi-cyclic matrix features and the coding can be achieve linear comolexity. The main content of this paper is aimed at the study of the theory of construction algorithm of QC-LDPC code and the performance analysis.First, the study of the basic theory of LDPC code, including the definition of LDPC code, structure algorithm, the encoding an decoding algorithm, and the basic concept of QC-LDPC code. The detailed and in-depth analysis can help grasp the LDPC code overall.Secondly, the construction algorithm of QC-LDPC code based on BIBD. The traditional algorithm based on BIBD, using correlation matrix between the block and the check matirx. Replaced the correlation matrix by the position vector, each elements of block is build relationships with the parity check matrix, thus the parity check matrix column is extended from 1 to 4. The above two algorithms are based on the finite field adder operation, a kind of construction algorithm of QC-LDPC code based on the multiplicative field and BIBD can be got with the power exponential instead of add operation of the primitive elements. The simulation results of the three algorithms shows that: the error correction performance is improved with the two improved algorithm under white gaussian noise channel; The rate of convergence is faster of the second improved algorithm in the iterative decoding.Finally, the construction algorithm of QC-LDPC code based on PEG. The PEG algorithm bansed on the Tanner graph is a random construction algorithm with the optimal performance and it’s very suitable for the LDPC code with a short length. By the matrix extension with the unit circle permutation sub-matrix, is can be used to construt the QC-LDPC code, and the size of the QC-LDPC codes is flexible according changing the size of the sub-matri. The error correction performance can be improvedwith shifting the parameter modification sub-matrices. Simulation results show: the performance of the improved error correction algorithm and the traditional algorithm is very similar, while the presence of sub-matrix improved the parameter selection and easier encoding.