  CC-GLPDC codes are a class of generalized low-density parity-check (GLDPC)
codes where the constraint nodes (CNs) represent convolutional codes. This
allows for efficient decoding in the trellis with the forward-backward
algorithm, and the strength of the component codes easily can be controlled by
the encoder memory without changing the graph structure. In this letter, we
extend the class of CC-GLDPC codes by introducing different types of
irregularity at the CNs and investigating their effect on the BP and MAP
decoding thresholds for the binary erasure channel (BEC). For the considered
class of codes, an exhaustive grid search is performed to find the BP-optimized
and MAP-optimized ensembles and compare their thresholds with the regular
ensemble of the same design rate. The results show that irregularity can
significantly improve the BP thresholds, whereas the thresholds of the
MAP-optimized ensembles are only slightly different from the regular ensembles.
Simulation results for the AWGN channel are presented as well and compared to
the corresponding thresholds.
