Check-hybrid GLDPC codes: Systematic elimination of trapping sets by super checks

In this paper, we propose a new approach to constructing a class of check-hybrid generalized low-density parity-check (GLDPC) codes which are free of small trapping sets. This approach is based on converting selected checks of an LDPC code involving a trapping set to super checks corresponding to a shorter error correcting component code. In particular, we follow two goals in constructing the check-hybrid GLDPC codes: First, the super checks are replaced based on the knowledge of trapping sets of the global LDPC code. We show that by converting only some single checks to super checks the decoder corrects the errors on a trapping set and hence eliminates the trapping set. Second, the number of super checks required for eliminating certain trapping sets is minimized to reduce the rate-loss. We first give an algorithm to find a set of critical checks in a trapping set of an LDPC code and then we provide some upper bounds on the minimum number of critical checks needed to eliminate certain trapping sets in the parity-check matrix of an LDPC code. A possible fixed set for a class of check-hybrid codes is also given.