A deterministic structure for controlled distribution of weight-2 columns is proposed for a parity-check matrix H that reduces the occurrence of undetected frame errors and significantly enhances the code performance in comparison to a randomly-constructed parity-check matrix. H comprises a non-deterministic section H.sub.1 and a deterministic section H.sub.2, and wherein H.sub.2 comprises a first part comprising a column h having an odd weight greater than 2, and a second part comprising matrix elements for row i, column j equal to 1 for i=j, 1 for i=j+1, 0 elsewhere.