Quasi-Cyclic Low-Density Parity-Check (QC-LDPC) codes require less hardware resources due to the quasi-cyclic structure of parity-check matrices. In this paper, two improved methods for constructing QC-LDPC codes are proposed. Firstly, in order to make sure the masked LDPC codes have flexible code rate and code length, an improved construction of masking matrix is presented. The proposed regular masking matrix of QC-LDPC codes have the girth at least 6. Then, the irregular codes are constructed by using improved finite field approach and PEG algorithm, which result in large girth and less short cycles. Simulations demonstrate that the proposed QC-LDPC codes have both lower error floor and good waterfall performance.
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