NPML Detection Combined with Parity-Based Post-Processing

The performance of magnetic recording sytems that include conventional modulation codes combined with multiple parity bits is studied. Various performance measures, including bit error
rate at the output of the inverse precoder, byte error probability at the input of the Reed-Solomon (RS) decoder and sector error rate, are used to evaluate the performance of various coding/detection schemes. Suboptimum detection/decoding schemes consisting of a 16-state noise-predictive
maximum-likelihood (NPML) detector followed by parity-based noise-predictive post-processing, and maximum-likelihood sequence detection/decoding on the combined channel/parity trellis are
considered. For conventional modulation codes, it is shown that although the dual-parity post-processor gains 0.5 dB over the single-parity post-processor in terms of bit- and byte-error-rate
performance, the sector-error-rate performance of both schemes is almost the same. Furthermore, the sector-error-rate performance of optimum 64-state combined channel/parity detection for the
dual-parity code is shown to be approximately 0.1 dB better than that of optimum 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 length or multiparity codes in conjunction with combined parity/channel detection are used.

Keywords: Noise-predictive maximum-likelihood detection, noise-predictive post-processing, parity check codes, sector error probability.