Error detection/correction and fault detection/recovery – Pulse or data error handling – Digital data error correction
Reexamination Certificate
1999-08-10
2002-02-19
Moise, Emmanuel L. (Department: 2784)
Error detection/correction and fault detection/recovery
Pulse or data error handling
Digital data error correction
C714S768000, C369S053310, C369S053320, C369S053350
Reexamination Certificate
active
06349400
ABSTRACT:
TECHNICAL FIELD
This invention related to an optical disc recording/reproducing method, an optical disc and an optical disc device.
BACKGROUND ART
Conventionally, optical recording media such as a disc-shaped optical recording medium and a card-shaped optical recording medium using an optical or magneto-optical signal recording/reproducing method have been developed and provided on the market. As such optical recording media, there have been known read-only memory type recording media such as a so-called compact disc (CD), so-called write-once type recording media which enable data writing once on the user side, and rewritable recording media which enable so-called overwrite such as a magneto-optical (MO) disc.
In an optical disc device for carrying out writing/reading of data onto/from a disc-shaped recording medium, a laser diode for emitting a light beam for information recording/reproduction and a photodetector for detecting a reflected light of a light beam radiated onto an optical disc are provided. Using an optical head on which focusing servo and tracking servo are performed on the basis of the detection output from the photodetector, speed servo is performed on a spindle motor and the optical disc is rotated at a constant angular velocity or a constant linear velocity while a recording track of the optical disc is scanned with a light beam, thereby carrying out data recording/reproduction.
In a magneto-optical disc system prescribed by the International Organization for Standardization (ISO), blocked codes are employed.
In the format of magneto-optical disc prescribed by the ISO, the direction of user data is equal to the direction of data on the disc as shown in FIG.
1
. In an ECC block using blocked codes, the direction of correction codes is interleaved with respect to the direction of data on the disc in order to improve the capability of correcting burst errors. Also, in this format, data immediately after frame synchronization FS belong to separate identical correction codes, and the second data from frame synchronization FS belong to separate identical error correction codes. Similarly, data immediately before frame synchronization FS belong to separate identical error correction codes.
At the time of recording on the optical disc of such a format, when all the user data sent from the application side for one ECC block is written into a buffer memory
302
through an arbiter
301
, as shown in
FIG. 2A
, an ECC processing section
303
starts error correction coding. After coding of all the data in one ECC block is completed, the coded data is sent from the buffer memory
302
to modulation means and channel encoding is started. Thus, channel-encoded data is recorded in the user data area on the disc.
At the time of reproduction, reproduction data obtained from the disc is channel-decoded by demodulation means. When all the data for one ECC block is written into the buffer memory
302
through the arbiter
301
, as shown in
FIG. 2B
, the ECC processing section
303
starts decoding. After decoding of all the data in one ECC block is completed, the user data is taken out from the buffer memory
302
and is sent to the application side.
As described above, in the magneto-optical disc system prescribed by the ISO, the direction of user data is equal to the direction of data on the disc, and the direction of error correction codes is interleaved with respect to the direction of data on the disc. Therefore, at the time of recording, error correction coding cannot be started unless all the user data for one block is written into the buffer memory. Unless coding of all the data in the block is completed, channel encoding of coded data cannot be started and hence channel-encoded data cannot be recorded onto the disc. At the time of reproduction, decoding cannot be started unless reproduction and channel decoding of all the reproduction data for one block are completed. Unless decoding of all the data in the block is completed, the user data cannot be taken out from the buffer memory. Thus, the latency time therefor is a fixed delay at the time of recording/reproduction. As the ECC block size increases, the fixed delay increases in proportion to the block size.
In the case where special recording/reproduction is carried out such as after-recording for reproducing, processing and then recording data during a short period of time by effectively utilizing the random accessibility as a feature of the optical disc, it is desired that the fixed delay at the time of recording/reproduction is as short as possible.
In the case of special recording/reproduction such as after-recording, it is necessary to have a buffer memory corresponding to the time required for data processing between reproduction operation and recording operation and for access on the disc, in order to carry out continuous reproduction operation at a high speed, data processing and then continuous recording operation for securing a transfer rate. Also, not only a transfer rate which is approximately twice higher is required for carrying out reproduction and recording operation, but also the transfer rate needs to be higher for the time required for data processing and for access on the disc.
In the case of after-recording, it is considered that data may be recorded at a position on the disc from where it is reproduced. In the case of continuous reproduction and recording, too, the recording position is close to the reproduction position. Therefore, only a short access time is required and the data processing time may be problematical. In general, a frame synchronizing signal FS is provided at the header part of a frame. If bit slip is generated, re-synchronization can be carried out by using the frame synchronizing signal FS. If bit slip is generated at a halfway point of a frame, the timing is shifted in the portion following that point and demodulation cannot be carried out accurately, or the position of demodulated data is shifted. As a result, a data error is generated. After that, when a frame synchronizing signal FS is detected at the header part of the next frame, the correct timing is obtained and the data is accurately reproduced. That is, the data immediately after the frame synchronizing signal FS is more resistant to an error caused by bit slip, in comparison with the data immediately before the frame synchronizing signal FS.
Meanwhile, there has been recently a remarkable increase in the capacity of the ROM (read only memory) disc and the RAM (random access memory) disc using optical recording. Shortening of the wavelength of a semiconductor laser used for the optical head of the optical disc recording/reproducing device and increase in the numerical aperture (NA) of an objective lens for condensing a light beam onto the information recording surface of the optical disc are realized.
Reduction in the spot size is known as a technique for realizing a high-density phase-change type optical disc having a capacity greater than that of a DVD-RAM. The spot size on the recording medium is substantially provided by &lgr;/NA, and can be reduced by a technique using a short-wavelength semiconductor laser light source made of GaN or ZnSe or a technique of increasing the NA of the objective lens by a two-group lens represented by a solid immersion lens (SIL).
For example, on the assumption of &lgr;=640 nm and NA=0.85, the diameter of the spot is approximately 0.75 &mgr;m on the medium. If signals are recorded/reproduced by using RLL(1, 7) modulation, a linear recording density of approximately 0.21 &mgr;m/bit can be realized.
As typical modulation codes of a modulation system having a broad detection window of the channel suitable for high-density recording/reproduction, an RLL(1, 7) code and an RLL(2, 7) code are known.
RLL(1, 7) modulation is a type of modulation with a run length limited (RLL) code having a finite maximum inversion interval of waveform string, in which the minimum run of bit information (symbol)
0
is 1 and the maximum run is 7.
In RLL(1, 7) modulation, when converting da
Moise Emmanuel L.
Smid Dennis M.
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