Near-capacity protograph doubly-generalized LDPC codes with block thresholds

Protograph doubly-generalized low-density parity-check (DGLDPC) codes, which allow for arbitrary component codes at the variable and check nodes of a protograph, are considered. Exact density evolution is derived over the binary erasure channel. Conditions on the protograph and component codes to ensure equality of block-error threshold and density evolution threshold for large-girth ensembles are established. Conditions for stability of density evolution are derived, and block-error threshold property is extended to binary-input symmetric channels. Optimized low-rate protographs for DGLDPC codes over the erasure channel are presented.