A modified concatenated coding scheme, with applications to magnetic data storage

When a block modulation code is concatenated with an error-correction code (ECC) in the standard way, the use of a modulation code with long blocklengths results in error propagation. This correspondence analyzes the performance of modified concatenation, which involves reversing the order of modulation and ECC. This modified scheme reduces error propagation, provides greater flexibility in the choice of parameters, and facilitates soft-decision decoding, with little or no loss in transmission rate. In particular, examples are presented which show how this technique ran allow fewer interleaves per sector in hard disk drives, and permit the use of more sophisticated block modulation codes which are better suited to the channel.