A decoding apparatus and method are described. The decoder includes N successive decoder groups numbered 1 to N arranged in series. Each decoder group includes primary decoding means for decoding the first sequence of codewords in combination with the source sequence of symbols to produce a sequence of primary decoded symbols; intermediate interleaving means for interleaving the sequence of primary decoded symbols using intra-block permutations on the source sequence of symbols and inter-block permutations on each intra-block permuted block across the predetermined number of the intra-block permuted blocks to produce a sequence of intermediate symbols; secondary decoding means for decoding the second sequence of codewords in combination with the sequence of intermediate symbols and a sequence of interleaved source symbols to produce a sequence of secondary decoded symbols; and de-interleaving means for de-interleaving the sequence of secondary decoded symbols to produce a sequence of estimated symbols.