A concatenated coding technique for partial response channels

A new concatenated coding technique has been developed for high-order PRML channels. Its first key feature is a pre-error-correction-coding (pre-ECC) scheme comprising cyclic-redundancy-check ECC (CRCC) coding and simplified soft-output decoding. The CRCC coding, a very-low-redundancy inner-block ECC concatenated to the PRML channel, specifically corrects dominant short error-events in the ML-detector. The soft-output decoding enhances the CRCC coding capability through the list and soft-symbol output Viterbi-algorithm (list-SOVA). A second key feature is an iterative decoding scheme to ensure efficient cooperation between an outer Reed-Solomon (RS) ECC and the ML-detector. By using error-free decoded bit-information feedback from the outer RS-ECC decoder, the iterative scheme employs "state pinning" in the ML trellis-detector. This enables long error-events remaining after the CRCC decoding to be corrected efficiently without increasing the coding redundancy and the decoding complexity. Complementary use of the iterative scheme for long error-events and the CRCC decoding for dominant short error-events improves the total system error-rate performance. Simulation showed that the concatenated coding scheme could significantly improve the RS-ECC error-rate performance of a 16/17-rate quasi-MTR-coded ME/sup 2/PRML channel when used in conjunction with CRCC coding.