Improved combining method for design of quasi-cyclic LDPC codes

An improved combining method is proposed for constructing quasi-cyclic low-density parity-check (QC-LDPC) codes with large girth and few short cycles. Large girth QC-LDPC codes can be obtained by carefully designing one component code with large girth. By properly designing the other component codes, a lot of QC-LDPC codes with very few short cycles can be designed. Simulations show that compared with Chinese remainder theorem based QC-LDPC codes and progressive edge-growth based QC-LDPC codes, the proposed QC-LDPC codes have much less short cycles and better performance.