Spectral graphs for quasi-cyclic LDPC codes

Quasi-cyclic codes are described in terms of code equations on the spectral components of constituent cyclic codes. These define a constraint graph in the spectral domain. Here spectral graphs define low density parity check codes (LDPC) codes for which minimum distance can be bounded with algebraic and graph-based arguments. Examples include [42,22,8] and [155,64,20] regular LPDC codes.