US 8,797,670 B2Granted

Adaptive soft-output detector for magnetic tape read channels

AssigneeInternational Business Machines Corporation

InventorsKatherine T. Blinick, Robert A. Hutchins, Thomas Mittelholzer, Sedat Oelcer

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Abstract

In accordance with one embodiment, a data storage system includes a tape channel for reading precoded data from a magnetic tape medium to produce a signal, a soft detector adapted for calculating first soft information about each bit of the signal and sending the first soft information to a soft decoder, and the soft decoder positioned subsequent to the soft detector, the soft decoder being adapted for calculating second soft information about each bit of the signal and sending the second soft information to the soft detector, wherein the precoded data includes a characteristic of being passed through at least one precoder prior to being written to the magnetic tape medium, and wherein the soft detector provides automatic compensation for the precoded data. Other systems, methods, and computer program products for reading data using an adaptive soft-output detector are described according to more embodiments.

Claims25

Dependent claims

A data storage system, comprising:

a tape channel for reading precoded data from a magnetic tape medium to produce a signal;
a noise whitening filter positioned subsequent to the tape channel and configured to pass the signal to a soft detector, wherein the noise whitening filter is configured to control variance of noise affecting the signal output from the filter, wherein the noise whitening filter processes the signal according to the following transfer polynomial:
W(D)=1−(p1D+ . . . +pλDλ), where p1 . . . Pλ are the noise whitening coefficients with the noise whitening filter having 2λ states, and where the tape channel is characterized by a transfer polynomial F(D)=1+f1D+ . . . +fLDL where D is delay corresponding to bit duration, with the tape channel having 2L states, L represents a memory length of the tape channel, and λ represents a memory length of the noise whitening filter;
the soft detector configured to calculate first soft information about each bit of the signal and sending the first soft information to a soft decoder;
and
the soft decoder positioned subsequent to the soft detector, the soft decoder being configured to calculate second soft information about each bit of the signal and sending the second soft information to the soft detector,
wherein the precoded data comprises a characteristic of being passed through at least one precoder prior to being written to the magnetic tape medium, and
wherein the soft detector provides automatic compensation for the precoded data.

5 more elements

A computer program product, comprising a non-transitory computer readable storage medium having computer readable program code embodied therewith, the computer readable program code comprising:

computer readable program code configured to read precoded data from a magnetic tape medium to produce a signal;
computer readable program code configured to pass the signal through a soft detector to calculate first soft information about each bit of the signal and to provide adaptive compensation for the precoded data;
computer readable program code configured to send the first soft information to a soft decoder;
computer readable program code configured to pass the signal through the soft decoder to calculate second soft information about each bit of the signal;
and
computer readable program code configured to send the second soft information to the soft detector,
wherein the precoded data comprises a characteristic of being passed through at least one precoder prior to being written to the magnetic tape medium, and
wherein the soft detector applies a Dual-Max (DMAX) algorithm comprising:
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wherein yk is the signal, ak denotes a bit in a bit sequence of the signal, ak(Sk) is an alpha term for a current state (Sk) in a forward recursion, ak(Sk−1) is an alpha term for a previous state (Sk−1) in the forward recursion βk(Sk) is a beta term for the current state in a backward recursion, βk−1(Sk−1) is a beta term for the previous state in the backward recursion, and LLR(ak) is an approximation of a log-likelihood term that calculates a posteriori probabilities.

192 more elements

Dependencies are inferred from the claim text.

Facts

Application: 13/527,508Filed 19 Jun 2012
Published: US 2013/0335846 A119 Dec 2013
Granted: 5 Aug 2014
Term ends: Not estimatedThe source records don’t support an estimate.

Classification8 codes

G11B 20/10046
Improvement or modification of read or write signals: filtering or equalising, e.g. setting the tap weights of an FIR filter
G11B 20/10074
Using partial response filtering when writing the signal to the medium or reading it therefrom: ePR4, i.e. extended partial response class 4,…
G11B 20/10287
Bit detection or demodulation methods: using probabilistic methods, e.g. maximum likelihood detectors
G11B 5/008
Recording by magnetisation or demagnetisation of a record carrier; Reproducing by magnetic means; Record carriers therefor: recording on, or…