Constructing Quasi-Cyclic LDPC codes Using a Search Algorithm

This article presents a search algorithm for constructing regular and irregular quasi-cyclic LDPC codes. Code rows and columns are divided into j (column weight) and k (row-weight) or more groups respectively. Rows or columns in a group are connected to the same group and in order of appearance. Grouping of rows and columns forms sub-matrices. The sequential row-column connections order creates a cyclic structure in sub-matrices. The row-column constraint is observed to avoid four-cycles. The proposed algorithm is flexible compared to other methods. It obtains codes over a wide range of girths, rates and lengths. Bit-error rate simulations show that obtained codes have good performance with randomly searched codes performing better that sequentially searched codes.