Data readout device and data readout method

Abstract

A data readout device generates decoded data based on a decided data bit decided by performing a hard-decision on likelihood data, wherein the likelihood data is generated in accordance with an iterative decoding method corresponding to a turbo-coding process. The iterative decoding process is performed on a sampled value obtained by sampling a signal read out from a magneto-optical disk at a predetermined sampling period. The data readout device is made up of a reliability determination part and an error correcting decoder. The reliability determination part detects whether each obtained data bit was obtained from likelihood data within a predetermined range defined with respect to a histogram of log likelihood ratios. When it is detected that a data bit was obtained by a hard-decision on likelihood data within the predetermined range, the data bit is regarded as being obtained by a hard-decision whose reliability is not sufficient. In this way, the error correcting decoder can perform ECC-based decoding operations including loss-correction processes depending on respective reliability-determination results that distinguish reliabilities among respective data bits. Thus, the accuracy of decoded data is increased. The data transfer rate of transferring decoded data when reading out of the MO medium is also improved to the utmost.

Description

BACKGROUND OF THE INVENTION[0001]1. Field of the Invention[0002]The present invention generally relates to data readout methods and devices, for example, magnetic disk drives, magneto-optical disk drives or other optical disk drives, and magnetic tape drives. More specifically, the present invention relates to a data readout scheme for reading out data from a data-recording medium by using an iterative decoding method, wherein the data-recording medium contains data recorded by a turbo-coding method.[0003]2. Description of the Related Art[0004]Turbo-coding methods have large encoding gains and are known in the telecommunication field. A typical turbo coding system can encode a data bit string “u” by using two encoders that perform recursive systematic convolutional coding. Such a turbo coding system is shown in FIG. 1. Another but still typical turbo coding system is shown in FIG. 2.[0005]The turbo coding system shown in FIG. 1 is made up of a first encoder 11, an interleaver “π1”12...

AI Technical Summary

Benefits of technology

[0081]Other features that may be employed to help further achieve the objects together with the advantageous effects of the present invention will become apparent by reference to the following detailed description when considered in connection with the accompanying drawings.

Problems solved by technology

When log likelihood ratios “L(u*)” that take place in accordance with this type of distribution curve are subjected to hard-decisions employing the value 0 as the slice level “L0”, decisions on log likelihood ratios “L(u*)” whose values are in the neighborhood of 0 are not necessarily correct.

Thus, possibly, some data may be incorrectly decoded.

However, such increase in the number of repetitions of the decoding process brings about an increase of time required for the data decoding processes, and, thus, the data transfer rate is reduced.

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