Noise predictive maximum likelihood detection combined with parity-based post-processing

The performance of magnetic recording systems that include conventional mod ulation codes combined with multiple parity bits is studied. Various perfor mance measures, including bit error rate at the output of the inverse preco der, byte error probability at the input of the Reed-Solomon (RS) decoder a nd sector error rate, are used to evaluate the performance of various codin g/detection schemes. Suboptimum detection/decoding schemes consisting of a 16-state noise-predictive maximum-likelihood (NPML) detector followed by pa rity-based noise-predictive post-processing, and maximum-likelihood sequenc e detection/decoding on the combined channel/parity trellis are considered, For conventional modulation codes, it is shown that although the dual-pari ty post-processor gains 0.5 dB over the single-parity post-processor in ter ms of bit- and byte-error-rate performance, the sector-error-rate performan ce of both schemes is almost the same. Furthermore, the sector-error-rate p erformance of optimum 64-state combined channel/parity detection for the du al-parity code is shown to be approximately 0.1 dB better than that of opti mum 32-state combined channel/parity detection for the single-parity code. These performance gains can be even more substantial if appropriate coding techniques that eliminate certain error events and minimize error burst len gth or multiparity codes in conjunction with combined parity/channel detect ion are used.