A check node processing unit configured to determine check node messages to decode a signal encoded using NB-LDPC code, the check node processing unit comprising: a data link to one or more message presorting units configured to determine permuted variable node messages by permuting variable node messages generated by one or more variable node processing units; a syndrome sub-check node configured to determine check node messages from a set of syndromes, the set of syndromes being determined from one or more intermediate messages computed from the permuted variable node messages; a forward-backward sub-check node configured to determine permuted check node messages from the intermediate messages; a switching unit configured to generate check node messages of given index from the check node messages or from the permuted check node messages depending on the giving index.