Quasi-Cyclic LDPC Codes Based on the Improved Combining Method

An improved combining method based on the Chinese Remainder Theorem is proposed for constructing much better quasi-cyclic (QC) LDPC codes. By carefully permuting the block columns of the parity check matrices of the component codes, a lot of QC-LDPC codes with much less short cycles and better performance can be designed. Simulation results show that at a BER of 10-6, the constructed QC-LDPC codes outperform those designed by the existing combining methods by about 1.2 dB.