Code conversion method and apparatus, code recording medium, code recording apparatus and code reproducing apparatus

Abstract

A code conversion method and apparatus is provided for scrambling and modulating data. The method and apparatus includes scrambling an input main data unit based on any of plural types of pseudo-random number sequences, and modulating the scrambled main data unit based on any of plural types of modulation data. An output main data unit is produced from the modulated main data unit, and a calculated value representing a difference between a number of 0 bits and a number of 1 bits included in the output main data unit is obtained. Any of the modulation data is then selected dependent upon the calculated value. The method and apparatus further includes determining whether or not a variation of the calculated value has exceeded a predetermined threshold, newly selecting another pseudo-random number sequence used for the step of scrambling if it is determined that the variation of the calculated value has exceeded the predetermined threshold value, and re-scrambling the input main data unit based on the newly selected pseudo-random number sequence.

Description

[0001]This application is a continuation of application is a reissue of 08 / 900,436 filed on Jul. 25, 1997, now U.S. Pat. No. 5,898,394.BACKGROUND OF THE INVENTION[0002]1. Field of the Invention[0003]The present invention relates to a code conversion method and apparatus for scrambling and modulating data, a code recording medium on which the scrambled and modulated data may be recorded and code recording and reproducing apparatus for recording / reproducing the scrambled and modulated data onto / from a recording medium.[0004]2. Description of the Related Art[0005]Optical disks have become very popular as recording media for recording various types of software data such as video data, audio data and computer data thereon. The optical disks include various kinds of read-only type disks such as a laser disk (LD), a compact disk (CD), a compact disk read-only memory (CD-ROM) and various kinds of rewritable and / or write-once type disks such as a magneto-optic disk, a phase change disk and a...

AI Technical Summary

Benefits of technology

[0055]First, according to the code conversion method of the present invention, if the variation of the calculated value representing a difference between the number of “0” bits and the number of “1” bits in the output main data word (i.e., the variation of a DSV) had exceeded the threshold value, another pseudo-random number sequence is newly selected and then the input main data word is re-scrambled. Thus, the pseudo-random number sequence is repeatedly changed and the scrambling is repeatedly performed until the DSV becomes equal to or smaller than the threshold value. As a result, the increase of DSV can be prevented and the low frequency components of the output main data word can be reduced. Therefore, when such an output main data word is recorded onto a recording medium and a signal is reproduced from the recording medium, it is possible to reduce the low frequency components of the reproduced signal and to prevent a reproduction error.

[0056]In addition, the second pseudo-random number sequences used for the step of re-scrambling are assumed to be pseudo-random number sequences making it possible to obtain a plurality of main data words not having the bit pattern causing the increase of DSV at a ratio equal to or larger than (M−N) / M. By obtaining the words not having the bit pattern in question at a ratio at least equal to (M−N) / M in this manner, the variation of the DSV can be reduced to a practical level.

[0058]Next, according to the code recording medium of the present invention, since scramble data and scrambled main data are recorded on a sector basis, the scramble data and the scrambled main data can be read from an arbitrary sector and the scrambled main data can be restored into original data in accordance with the scramble data. Thus, the initial value of any arbitrary pseudo-random number sequence may be recorded as the scramble data onto each sector. Moreover, since the scramble data represents the initial value of the pseudo-random number sequence and the pseudo-random number sequence is composed of random numbers beginning with the initial value, the main data can be recorded after the main data has been sufficiently scrambled. As a result, the low frequency components of a signal to be recorded onto a sector can be reduced and it is possible to prevent the same signal from being repeatedly written onto the same sector.

[0061]Thus, the invention described herein makes possible the advantages of (1) providing code conversion method and apparatus which can reduce the low frequency components of a signal to be recorded onto a recording medium by controlling the pseudo-random number sequences such that the divergence of a DSV can be suppressed and that substantially the same signal is not repeatedly rewritten onto the same sector, (2) providing a code conversion recording medium onto / from which a signal is recorded / reproduced in accordance with the improved code conversion method of the present invention, and (3) providing a code conversion recording / reproducing apparatus used for recording / reproducing the signal onto / from such a recording medium.

Problems solved by technology

As a result, a read margin is adversely decreased and the quality of a reproduced signal is more likely to be degraded.

However, even when any of these coding methods is applied, a data pattern having low frequency components which cannot be reduced may still appear for a long duration in some cases.

However, though the above-described prior art code conversion apparatus can surely reduce the low frequency components of a reproduced signal and the possibility of the abnormal increase of the low frequency components, the degree of the reduction is not satisfactorily high and a reproduction error may continue to occur in some cases.

Thus, if 16-bit main data words having such bit patterns successively appear, then the DSV adversely increases or decreases to diverge.

As a result, the low frequency components of the output main data words are disadvantageously increased.

That is to say, in the prior art code conversion apparatus, though the input main data is scrambled and the scrambled main data is subjected to an 8 / 16 modulation, the low frequency components of the main data cannot be satisfactorily reduced.

Consequently, when the main data is reproduced from a recording medium on which the main data has been recorded, the low frequency components of the reproduced signal increase, the envelope of the reproduced signal abruptly varies, and a reproduction error occurs.

Even if the envelope of the reproduced signal is corrected or the main data is corrected by using an error correction code (ECC) to be added thereto, such a reproduction error cannot be totally prevented.

In such a case, since the characteristics of a part of the recording medium occupied by the sector in question become nonuniform, the S / N ratio of the reproduced signal is decreased and a reproduction error occurs in some cases.

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