Error detection/correction and fault detection/recovery – Pulse or data error handling – Digital data error correction
Reexamination Certificate
1998-04-09
2001-02-20
Baker, Stephen M. (Department: 2784)
Error detection/correction and fault detection/recovery
Pulse or data error handling
Digital data error correction
Reexamination Certificate
active
06192502
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an information reproducing apparatus such as a magneto-optic disc apparatus, in particular, to an information reproducing apparatus using PRML (Partial Response Maximum Likelihood) method and a reproducing method thereof.
2. Description of the Related Art
In an information reproducing apparatus such as a magneto-optic disc apparatus, as a method for decoding a signal reproduced from a record medium, Viterbi decoding method has been widely used. The Viterbi decoding method is a decoding method for decreasing a bit error rate that takes place in decoding a reproduced signal having a white noise.
Next, an outline of the Viterbi decoding method will be described. A plurality of statuses corresponding to a recording method for a record medium are identified beforehand. The maximum likelihood transition among such statuses is selected by a calculating process corresponding to a signal reproduced from a record medium. Such maximum likelihood transition is selected by an ACS (Adding, Comparing, and Selecting circuit) of a Viterbi decoder. The ACS estimates the maximum likelihood status transition from status transitions equal to the number of statuses. A PMU (Path Memory Unit) that has path memories equal to the number of statuses is disposed on the next stage of the ACS. The PMU generates decoded data as a sequence of decoded data values “1” or “0” corresponding to status transitions equal to the number of statuses from which the ACS estimates the maximum likelihood status transition.
The status transitions equal the number of statuses from which the ACS estimates the maximum likelihood status transition match each other. However, when the quality of a reproduced signal is not good, the status transitions may not match. When they do not match, a settled status transition cannot be obtained. Decoded data that path memories of the PMU generate corresponding to the settled status transition does not match and the reliability thereof is low.
Conventionally, since the ACS cannot recognize status transitions from which it estimates the maximum likelihood status transition, a process corresponding to matches/mismatches of decoded data equal to the number of statuses that are output from the PMU is performed. In other words, assuming that decoded data always matches, decoded data that is output from one of path memories is supplied to the next stage. Alternatively, decoded data that is determined as the most adequate decoded data by the rule of majority is selected from decoded data that is output from all the path memories and the selected decoded data is supplied to the next stage.
In the conventional Viterbi decoder, decoded data corresponding to a status transition is generated. However, since status data that represents the status transition itself is not generated. Thus, the maximum likelihood status transition estimated by the ACS is not recognized. Consequently, it is impossible to evaluate the reliability of decoded data and the signal quality of a reproduced signal corresponding to the maximum likelihood status transition estimated by the ACS.
As described above, the reliability of decoded data should be evaluated depending on whether the status transitions equal to the number of statuses from which the ACS actually estimates the maximum likelihood status transition match each other (namely, whether or not a settled status transition is obtained). To perform such an evaluation, status data that represents status transitions should be generated.
OBJECTS AND SUMMARY OF THE INVENTION
Therefore, an object of the present invention is to provide an information reproducing apparatus that generates status data that represents the maximum likelihood status transition selected by a calculating process corresponding to a reproduced signal value in Viterbi decoding method, generates decoded data corresponding to the generated status data, and evaluates the reliability of the decoded data and the signal quality of the reproduced signal corresponding to the status data and to provide a reproducing method thereof.
According to the present invention, there is provided an information reproducing apparatus for reproducing data that has been RLL (Run Length Limited) encoded and recorded on a record medium corresponding to Viterbi decoding method, comprising branch metric calculating means for calculating branch metrics for all statuses at a particular time point corresponding to an input reproduced signal, path metric updating means for selecting the maximum likelihood path metric of each of the statuses corresponding to values of which the branch metrics and the preceding path metrics are added, for outputting a first selection signal corresponding to the selected result, and for outputting a second selection signal corresponding to the minimum values of the path metrics, status data generating means, having a plurality of status memories corresponding to the respective statuses, for updating status data that represents the statuses corresponding to the first selection signal, status data selecting means for selecting the most adequate status data from the status data stored in the status memories corresponding to the second selection signal and for outputting the selected status data, and data decoding means for outputting decoded data corresponding to the selected status data and the just preceding status data.
According to the present invention, there is provided a many-value many-status Viterbi decoding apparatus for use with four-value four-status Viterbi decoding method with a waveform equalizing characteristic of PR(B, 2A, B), comprising an ACS circuit having adding devices for adding branch metrics of individual statuses and past path metrics, a comparing and selecting device for comparing output data of the adding devices and selecting the maximum likelihood path metric, and a storing circuit for storing the selected path metric, a status memory circuit, having a plurality of status memories corresponding to the individual statuses, for generating status data that represents a status transition corresponding to the selected path metric, and a selecting circuit for selecting one of the status data stored in the status memories and outputting the selected status data.
According to the present invention, there is provided a many-value many-status Viterbi decoding method with a waveform equalizing characteristic of PR(B, 2A, B), comprising the steps of (a) selecting a path metric with the minimum value from statuses corresponding to values of which branch metrics of the individual statuses and past path metrics are added, (b) storing transitions of the individual statuses selected as status data corresponding to the selected path metric, and (c) selecting the most adequate status data from the stored status data and outputting the selected status data.
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Chiba Takayoshi
Horigome Junichi
Yamaguchi Shigeo
Baker Stephen M.
Limbach & Limbach LLP
Sony Corporation
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