A modified E/sup 2/PRML (ME/sup 2/PRML) channel is optimized for high-density magnetic recording in order to reduce long error-propagation events in an ML detector. A cyclic redundancy-check error-correction code (CRCC), an innerblock ECC concatenated to the ML detector, is introduced as a new ECC-coding scheme for the high-order partial response maximum likelihood (PRML) channel. The CRCC coding can efficiently improve the BER performance with only a few redundant check-bits which intensively correct most-dominant short error-events in the ME/sup 2/PRML detector. A 16/17 coded ME/sup 2/PRML channel in conjunction with a 2.9% redundant CRCC coding can achieve a gain of more than 35 dB over a conventional 16/17 coded EPRML channel at a user density of 2.8.
The short-term iterative decoding implementation proposed in this paper not only uses conventional long-distance Reed-Solomon codes (RS codes), but also uses short-distance RS codes consisting of redundant symbols P and Q periodically inserted into the data in 512-byte sectors. A single parity matrix composed of redundant symbol P is decoded by using a belief propagation algorithm (BPA) such as low density parity check (LDPC) decoding. The Bahl-Cocke-Jelinek-Raviv (BCJR) algorithm is used for EEPR4 channel decoding. Serial iterative decoding is done by using log likelihood ratios produced by both algorithms. Simulations of the use of 28 redundant symbols of the short-distance RS codes and 30 symbols of the long-distance RS codes have confirmed that at a block error rate of about 10/sup -1/ (bit-error rate) /spl ap/10/sup -3/ the proposed system can reduce the block error rate more than tenfold. Consequently, one block erasure correction including 30 symbols per sector can be achieved at the same error rate.
A soft-output data-detection scheme optimized for data-dependent media-noise recording channels is investigated that uses signal-dependent correlation-sensitive (SDCS) metric computation for post-processing decoding. This media-noise soft-output (MNS) decoding scheme achieves suboptimal maximum-likelihood (ML) sequence detection in a nonstationary media-noise channel, while still using traditional Viterbi detection. Because it drastically reduces SDCS metric computation by focusing on correcting only the dominant error events in the ML detector, it is less complex than other suboptimal detection schemes. Moreover, the MNS decoding scheme provides parity-check-code decoding with more reliable soft-output information. Simulation showed that MNS decoding in conjunction with a conventional ME/sup 2/PRML system, provides an excellent tradeoff between data-detection performance and computation complexity for a jitter-noise dominant high-density recording channel.
A new iterative decoding scheme was developed for the cyclic redundancy check error correction code (CRCC), a concatenated error correction coding system. This simple iterative decoder achieves efficient cooperation between an outer Reed-Solomon error correction code (RS-ECC) decodes and a PRML trellis-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 in the ML-decoded data to be corrected efficiently without adding extra coding redundancy and specific decoding complexity. The iterative scheme improves the correction capability of the outer RS-ECC coding by making use of a CRCC coding for specific correcting short error-events. Simulation shows that the iterative scheme achieves significant improvement in RS-ECC error-rate performance for a rate 16/17 quasi-MTR-coded Modified E/sup 2/PRML (ME/sup 2/PRML) channel in conjunction with CRCC coding.
Read/Write characteristics are studied using a newly developed 1 micron trackwidth inductive-write/MR-read dual-element head and a Co-Cr-Pt/Co-Cr-Pt-Si dual-layered low noise medium. The 8/9 block coding, extended class IV partial response signalling and Viterbi detection are applied to the read/write data channel. A linear density of 120 kBPI with a bit error rate of 10-8 is achieved from ontrack measurements at a magnetic spacing of 0.08 μm. The possibility of a 1.5 μm track pitch(16.9 kTPI) is discussed based on offtrack measurements. The present head-medium system showed a sufficient track density resolution of 16.9 kTPI.
'%3e%3cpath fill='%23012169' d='M0 0v30h60V0z'/%3e%3cpath stroke='%23fff' stroke-width='6' d='m0 0 60 30m0-30L0 30'/%3e%3cpath stroke='%23C8102E' stroke-width='4' d='m0 0 60 30m0-30L0 30' clip-path='url(%23b)'/%3e%3cpath stroke='%23fff' stroke-width='10' d='M30 0v30M0 15h60'/%3e%3cpath stroke='%23C8102E' stroke-width='6' d='M30 0v30M0 15h60'/%3e%3c/g%3e%3c/svg%3e)