Explicit Construction of Type-II QC LDPC Codes with Girth at least 6
Kristine Lally · 2007
Type-II quasi-cyclic (QC) LDPC codes are constructed from combinations of weight-0, weight-1 and weight-2 circulant matrices. The structure of cycles of length 2nare investigated, and necessary and sufficient conditions for a type-II QC LDPC parity check matrix H to have girth at least 2(n+ 1) are given. An explicit construction of type-II codes which guarantees girth at least 6 is presented. A necessary and sufficient condition for a QC matrix with one or more rows of circulants, to be fullrank is derived.