Morishi Izumita

Digital Video Recording Techniques Using 1/2 Inch Metal Particle Tape

During the past ten years, rapid progress has been made in development of recording techniques for home use VTR. Nevertheless, a limit has now been reaches to improvement in such functional areas as SN ratio, resolution, and dubbing. It is now expected that digital recording techniques will be introduced into the video field in the future to assure even further development.

A simulation study of adaptive reception schemes for high-density digital magnetic storage

At high information densities, digital magnetic recording systems may be seriously hampered by channel imperfections such as intersymbol interference, noise, fading, nonlinearities, crosstalk, and overwrite noise. For such compound disturbance constellations, theoretical analysis of receiver performances becomes difficult. As an alternative, the digitized output signal of an experimental high-density digital videotape recorder is used to compare various promising receiver types by simulation. Apart from adaptive versions of the linear and decision feedback equalizers, adaptive variants of the Viterbi detector are studied, including new ones with resistance to nonlinearities and channel fading. Improvements of up to about 5 dB in effective signal-to-noise ratio over nonadaptive linear equalization are found to be within reach under worst-case operating conditions. >

Partial-response decoding of rate 1/2 modulation codes for digital storage

In digital storage systems, receivers for rate 1/2 modulation codes are usually oversampled by a factor of two with respect to the data stream that they attempt to reconstruct. It is shown that oversampling may be avoided by using partial-response techniques to detect, instead of the encoded binary signal, a decimated ternary one, from which the original data can be recovered by means of a simple decoder. A method is described to find all such decoders for a given rate 1/2 code. Examples treated are FM, MFM, Miller-squared,

Adaptive DCT coding for home digital VTR

The authors investigate fixed adaptive discrete cosine transform (FADCT) coding for use in digital VTRs (video tape recorders). The image is divided into 8*8-pixel subblocks, and a two-dimensional DCT is performed on each of them. The quantization scheme is adapted to input image data, thereby increasing coding efficiency. The scheme is designed, however, to keep the output data rate fixed. Computer simulation showed that FADCT coding improves the SNR (signal/noise ratio) from 1 dB to 3 dB as compared to nonadaptive DCT coding, and a high-quality image with SNR over 40 dB can be obtained at 3 bits/pixel. Reallocations of the extra bits from the higher to the lower AC energy subblocks allow the application of adaptive coding to the digital VTR, with a high tolerance for channel errors.<<ETX>>

Soft-output post-processing detection for PRML channels in the presence of data-dependent media noise

A soft-output data-detection scheme optimized for data-dependent media-noise recording channels is proposed that uses signal-dependent correlation-sensitive (SDCS) metric estimation for post-processing decoding. This media-noise soft-output (MNS) decoding scheme achieves sub-optimal maximum-likelihood (ML) sequence detection in a non-stationary media-noise channel, while still using traditional Viterbi detection. Because it drastically reduces SDCS metric computation by focusing on only specified dominant error-events in the ML detector, it is less complex than other sub-optimal detection schemes. Moreover, its one-shot post-processing scheme enables the use of a simple lookup-table architecture suitable for high-speed circuit implementation. Simulation shows that the MNS decoding scheme in conjunction with a conventional ME/sup 2/PRML system provides an excellent tradeoff between data-detection performance and computation complexity for a media-noise-dominant high-density recording channel.

Practical iterative decoding scheme using Reed-Solomon codes for magnetic recording channels

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.

Experiments on automatic equalizer without increased noise for digital recording systems.

ディジタル記録システムで発生する符号間干渉 (ISI) を雑音の増加なく除去できる等化器を開発した.本等化器は下記2つの手法で構成している. (1) 識別再生信号を用いてISIのコピーを作成し, これを元の信号から差し引くことでISIを除去する.この後, 再度識別再生し, データを復元する, (2) 復元データ中の符号誤りの位置を上記2種の識別再生信号をモジュロ2加算すすことで検出する.つぎに, この誤り位置に対応する符号の信頼度を再生信号の振幅値の大小に基づき判定し, 誤りを訂正する.実験とシミュレーションにより, 本等化器は再生信号の符号誤り率が10-2の場合に, これを約2桁改善できることを示した.同時に, 自動等化のためのディジタル, アナログいずれの回路構成でも使用できる簡易タップ係数収束アルゴリズムを提案し, その妥当性を解析した.これを用いて, 46Mb/sの高速動作可能なディジタル自動等化器を構成し, 良好な収束特性が得られることを示した.