Low complexity architecture for syndrome-based check node, SB- CN, processing in Extended Min-Sum, EMS, decoders for Non-Binary LDPC, NB-LDPC, codes using the principle of pre-sorting the variable messages based on a reliability criteria. Embodiments of the invention provide a check node processing unit (25) configured to determine at least one check node message to decode a signal encoded using a NB-LDPC code, the check node processing unit comprising: • a data link to one or more message presorting units (24) configured to determine permuted variable node messages by applying one or more permutations to at least three variable node messages generated by one or more variable node processing units (23); • a syndrome calculation unit (26) configured to determine a set of syndromes from the at least three permuted variable node messages, a syndrome comprising binary values; • a decorrelation and permutation unit (27) configured, for each check node message of a given index, to: • · Determine a permuted index by applying to said given index the inverse of the one or more permutations; • · Select at least one valid syndrome in the set of syndromes, a valid syndrome comprising a binary value associated with said permuted index equal to a given value; • · Determine, at least one candidate check node component from said at least one valid syndrome; • a selection unit (28) configured to determine at least one check node message from said at least one candidate check node component.
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