A structured parity-check matrix H is proposed, wherein H is an expansion of a base matrix H.sub.b. Base matrix H.sub.b comprises a section H.sub.b1 and a section H.sub.b2. Section H.sub.b2 comprises column h.sub.b having weight w.sub.h>=3 and H'.sub.b2 having a dual-diagonal structure with matrix elements at row i, column j equal to 1 for i=j, 1 for i=j+1, and 0 elsewhere. The 1's of h.sub.b and H.sub.b1 are arranged such that one or more groups of the rows of H.sub.b can be formed so that the rows of H.sub.b within each group do not intersect. Further more, the rows of base matrix H.sub.b can be permuted such that every two consecutive rows do not intersect.