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.

1 - 21 . (canceled) 
   
   
       22 . A method of reading out data from a data recording medium that stores encoded data encoded by a turbo-coding method, comprising the steps of:
 obtaining sampled values by performing sampling on signals from said recording medium;   generating likelihood data from said sampled values by an iterative decoding method, wherein said iterative decoding method corresponds to said turbo-coding method;   obtaining a data bit by performing a hard-decision on said likelihood data;   setting a slice level that divides a predetermined distribution of likelihood data into a reliable range of likelihood data and an unreliable range of likelihood data;   generating flag data on said data bit by comparing said likelihood data used for obtaining said data bit with said slice level;   choosing one error correction method by making reference to said flag data, wherein said error correction method is selected from an error-check-and-correction method, and a loss-correction method, wherein said error-check-and-correction method comprises error checking and error correction, wherein said loss-correction method comprises loss-correction without performing error check; and   generating decoded data by performing error correction on data that include said data bit using said error correction method chosen in said choosing step.   
   
   
       23 . A prerecorded program-storage medium storing a computer program,
 wherein when said computer program is executed in a computer, said computer program makes it possible for said computer to read out data stored on a data recording medium, said data encoded by a turbo-coding method;   wherein said computer program running on said computer reads out said data from said data recording medium in accordance with the steps of:   obtaining sampled values by performing sampling on signals from said recording medium;   generating likelihood data from said sampled values by an iterative decoding method, wherein said iterative decoding method corresponds to said turbo-coding method;   obtaining a data bit by performing a hard-decision on said likelihood data;   setting a slice level that divides a predetermined distribution of likelihood data into a reliable range of likelihood data and an unreliable range of likelihood data;   generating flag data on said data bit by comparing said likelihood data used for obtaining said data bit with said slice level;   choosing one error correction method by making reference to said flag data, wherein said error correction method is selected from an error-check-and-correction method, and a loss-correction method, wherein said error-check-and-correction method comprises error checking and error correction, wherein said loss-correction method comprises loss-correction without performing error check; and   generating decoded data by performing error correction on data that include said data bit using said error correction method chosen in said choosing step.