Method and system for optical disk decoding

Details Method and system for optical disk decoding Method and system for optical disk decoding

2000-12-22

2004-04-13

Lamarre, Guy J. (Department: 2133)

Error detection/correction and fault detection/recovery

Pulse or data error handling

Digital data error correction

C714S785000

Reexamination Certificate

active

06721917

ABSTRACT:

This application incorporates by reference Taiwanese application Serial No. 89111797, filed Jun. 16, 2000.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a method and system for digital versatile disk (DVD) decoding, and more particularly to a method and system for improving the error correcting rate and speed of DVD decoding.
2. Description of the Related Art
Referring now to
FIG. 1
, it illustrates a block diagram of conventional DVD encoding and decoding respectively. In the DVD encoding, firstly, a data message is inputted into an error detection code (EDC) appending unit
102
, resulting in a data block which is formed by appending an EDC to the data message. The data block is then inputted into a scrambler
104
for scrambling the data block. After scrambling, sixteen scrambled data blocks are inputted into an outer code encoder
106
for outer code encoding, thus outputting an outer-code parity (PO). Next, the sixteen scrambled data blocks and PO are inputted into an inner code encoder
108
for inner code encoding, thus outputting an inner-code parity (PI). Then, this sixteen scrambled data blocks, PO and PI comprise an error correction code (ECC) block. After inputting the ECC block into an eight-to-fourteen modulation (EFM) modulator
110
for eight-to-fourteen modulation, the modulated ECC block is stored in a DVD
112
.
As for DVD decoding, it is the reverse process of the DVD encoding. Firstly, data read from the DVD
112
are transferred to EFM demodulator
114
for performing eight-to-fourteen demodulation, obtaining an ECC block. The ECC block is then inputted into the inner code decoder
116
for inner code decoding. Next, the inner code decoded ECC block is transferred to the outer code decoder
118
for outer code decoding, resulting in a number of scrambled data blocks. The de-scrambler
120
then descrambles the scrambled data blocks, outputting a number of data blocks. Finally, before outputting the data blocks, they are checked by an EDC check unit
122
.
Referring to
FIGS. 2A-2B
, they illustrate a data sector before scrambling and an ECC block respectively. In
FIG. 2A
, a data sector
200
contains 12 row×172 column data symbols, i.e. a row in the data sector
200
contains 172 bytes. Besides, there is a four-byte EDC followed by the twentieth row in the data sector.
In
FIG. 2B
, it shows that source data
204
consists of sixteen scrambled data sectors, each of which is designated by numeral
1
to
16
respectively. The source data
204
has 192 rows of data and each row contains 172 bytes, i.e. the source data
204
contains 172 columns of data. When performing outer code encoding, the outer code encoder
106
processes the source data
204
according to the Y-direction, obtaining outer code parity following the columns of the source data
204
. The outer code parity, or PO, contains 16 rows of 172-byte data, corresponding to the 172 columns of the source data
204
. The source data
204
and the PO are designated a Reed-Solomon (RS) outer code. When performing inner code encoding, the inner code encoder
108
processes the source data
204
and the PO according to the X-direction, obtaining inner code parity following the rows of the source data
204
. The inner code parity, or PI, has 208 (=192+16) rows of 10-byte data, corresponding to the 208 rows of the source data
204
and PO. The source data
204
, PO and PI comprise the ECC block
206
.
Referring to
FIG. 3
, it shows a DVD decoding system according to the process shown in
FIG. 1
, in block diagram form. Firstly, an EFM demodulator
304
receives and processes message data read from DVD
302
, obtaining the ECC block
206
. The ECC block
206
is then delivered through bus
306
to data buffer
308
for storage. Next, inner code decoder
310
reads the ECC block
206
from the data buffer
308
and performs inner code decoding for detecting and correcting errors of the ECC block
206
. After that, the inner code decoder
310
writes the corrected data into the data buffer
308
. Outer code decoder
312
then reads the corrected ECC block
206
from the data buffer
308
and performs outer code decoding for detecting and correcting errors of the source data
204
in the ECC block
206
. After that, the outer code decoder
312
writes the corrected data into the data buffer
308
.
Next, descrambling and EDC checking unit
314
reads the source data of the ECC block
206
, which are scrambled when encoding, from the data buffer
308
for performing descrambling and EDC check. When the host requests for reading the source data of the data buffer
308
, descrambler
316
reads the ECC block
206
from the data buffer
308
for descrambling and then sends the descrambled source data to the host. It is desired to reduce the times of access to the data buffer
308
so that, in the decoding process above, the descrambling and EDC checking unit
314
performs descrambling and EDC check at the same time. Besides, when the EDC check result of the descrambling and EDC checking unit
314
indicates that the source data are corrected, the source data (after descrambling and EDC checking unit
314
) are delivered to the host.
In the conventional DVD decoding system described above, there are disadvantages as follows.
1. A data buffer is necessary for every stage of the decoding in the system where respective components share one data buffer. During the decoding, it is required to access to the data buffer for a number of times, resulting in a limitation in the speed of DVD decoding.
2. It is known that the error correction capability of the DVD decoding system can be improved by repeating the inner code and outer code decoding. However, the repetition of the inner code and outer code decoding is time-consuming, and thus the speed of the decoding will be lowered. Since the decoding system cannot differentiate between the region of data which has erroneous data and the region which has not in the source data
204
, the inner code or outer code decoding can only be performed for the whole source data
204
for each decoding.
3. If there are too much erroneous data to be corrected, the results of the inner code and outer code decoding may still be mistaken, leading to a situation that some of the data become erroneous after error correction.
SUMMARY OF THE INVENTION
It is therefore an object of the invention to provide a method and system for optical disk decoding by adjusting the sequence of the decoding and performing error detection code (EDC) checking during inner code decoding. In this way, it reduces the memory access time, increases the decoding speed, and improves the error correction capability.
According to the object of the invention, it provides a method for optical disk decoding, which is for decoding an error correction code (ECC) block. The method includes the steps as follows.
(a) It is determined whether it is to perform outer code decoding first. If so, the method proceeds to step (b). If not, the method proceeds to step (d).
(b) Inner code decoding and EDC checking is performed.
(c) It is determined whether one of the conditions is true: (1) error correction is complete; (2) the number of errors is over the limitation of error correction so that the error-correcting operation cannot be performed; or (3) the decoding operations are performed for a number of times but the correction is not complete. If so, the method proceeds to step (f); if not, the method proceeds to step (d).
(d) Outer code decoding is performed.
(e) It is determined whether one of the following is true: (1) the error correction is complete; (2) the number of errors is over the limitation of error correction so that the error-correcting operation cannot be performed; or (3) the decoding operations are performed for a number of times but the correction is not complete. If so, the method proceeds to step (f); if not, the method proceeds to step (b).
(f) Descrambling is performed.
(g) EDC checking is performed.
According to the object of the invention, it provides a metho

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