Reproduced signal evaluating method, information recording medium, reproducing device, and recording device

Abstract

A reproduction signal evaluation method according to the present invention relates to adjustment of an edge portion between a shortest mark and a shortest space in a data sequence including marks and spaces in combination that is recordable on an information recording medium. In a pattern including a shortest mark and a shortest space adjacent before or after the shortest mark, a shift amount of an edge of the shortest mark is obtained from a differential metric calculated regarding one of a first pattern in which a space adjacent to the shortest mark and not adjacent to the shortest space is longer than the shortest space; and a second pattern in which a mark adjacent to the shortest space and not adjacent to the shortest mark is longer than the shortest mark.

Description

TECHNICAL FIELD[0001]The present invention relates to a signal processing method using maximum likelihood decoding and a method for evaluating an information recording medium using maximum likelihood decoding.BACKGROUND ART[0002]Recently, as the recording density for information recording mediums is being improved, the shortest mark length of recording marks is approaching the limit of the resolving power, which relies on a detection system.[0003]In the case where, for example, an information recording medium is an optical disc medium, the “resolving power, which relies on a detection system” means an optical resolving power, which relies on the size of an optical spot generated by collecting laser light.[0004]Due to the limit of the resolving power, increase of the inter-code interference and deterioration of SNR (Signal to Noise Ratio) are more conspicuous. As a result, a PRML (Partial Response Maximum Likelihood) method or the like is now used generally as a signal processing met...

AI Technical Summary

Benefits of technology

[0059]According to the present invention, a shift amount of the edge of the shortest mark of a 2T / 2T portion, which is a 2T-continuous pattern, is obtained by calculating a differential metric of a pattern including a 3T or longer mark or space provided before or after the 2T / 2T portion. Owing to this, even where a sufficient signal fluctuation of the 2T / 2T portion is not obtained, the shift amount of the edge of the shortest mark of the 2T / 2T portion can be detected.

[0060]The present invention is directed to a signal evaluation method, usable for an information recording medium having a data sequence including a mark and a space located alternately, for generating a binary signal from a signal obtained by reproducing the data sequence using a PRML signal processing method and evaluating a likelihood of the binary signal. From the binary signal, a differential metric which is a difference of a reproduction signal from a first state transition path having a maximum likelihood and a second state transition path having a second maximum likelihood is calculated. The differential metric is classified to any of a plurality of data patterns each including at least one mark and at least one space. The data pattern classification to any of a plurality of data patterns is performed using a combination of a length of a first mark included in the data sequence and a length of a first space adjacently located immediately previous or immediately subsequent to the first mark, and is further performed using a length of a second mark which is not adjacent to the first mark and located adjacent to the first space. Thus, a reproduction signal quality of the information recording medium is evaluated, and an index for an edge shift of each data pattern including at least one edge can be provided.

[0061]The present invention is also directed to a signal evaluation method, usable for an information recording medium having a data sequence including a mark and a space located alternately, for generating a binary signal from a signal obtained by reproducing the data sequence using a PRML signal processing method and evaluating a likelihood of the binary signal. From the binary signal, a differential metric which is a difference of a reproduction signal from a first state transition path having a maximum likelihood and a second state transition path having a second maximum likelihood is calculated. The differential metric is classified to any of a plurality of data patterns each including at least one mark and at least one space. The data pattern classification to any of a plurality of data patterns is performed using a combination of a length of a first mark included in the data sequence and a length of a first space adjacently located immediately previous or immediately subsequent to the first mark, and is further performed using a length of a third space which is not adjacent to the first space and located adjacent to the first mark. Thus, a reproduction signal quality of the information recording medium is evaluated, and an index for an edge shift of each data pattern including at least one edge can be provided.

Problems solved by technology

In the meantime, because the signal processing method is now changed from the level determination method to the PRML method, problems occur in the evaluation method of a reproduction signal.

Therefore, occasionally, jitter may not be correlated with the decoding capability of the PRML method, which is based on a different signal processing algorithm from the level determination method.

When the distributions are summed up, it appears that the SN component is poor.

As described above, as the recording density of information recording mediums is more improved, the problems of the inter-code interference and SN deterioration will be more serious.