Error detection/correction and fault detection/recovery – Pulse or data error handling – Digital data error correction
Reexamination Certificate
2000-02-10
2002-09-17
Chung, Phung M. (Department: 2133)
Error detection/correction and fault detection/recovery
Pulse or data error handling
Digital data error correction
Reexamination Certificate
active
06453439
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to apparatus and method for encoding and decoding pseudo product code, suitable for use in digital devices which use pseudo product codes, such as a digital video tape recorder, digital audio recorder, digital communication device, or the like. More particularly, the present invention is concerned with a pseudo-product code encoding and decoding apparatus and method in which decoding processing is performed after a conversion of a pseudo-product code into a product code, so as to improve error correction capability.
2. Description of the Related Art
Recording/playback apparatuses such as digital video tape recorders and digital audio recorders, which digitize input video signals and audio signals and record the resultant digital signals, are put into use in recent years.
Referring to
FIG. 15
, a typical known recording/playback apparatus of the kind mentioned above, denoted by
200
, has a video signal code encoding unit
201
which, upon receipt of a video signal, encodes the video signal to form video data. The video data is delivered to an error correction code encoding unit
202
which performs an error-correction encoding on the video data. The video data output from the error correction code encoding unit
202
is supplied to a recording/playback unit
203
in which the video data is recorded in a magnetic tape
206
by means of a rotary head
207
.
In playback mode of operation of the recording/playback apparatus
200
, video data recorded in the magnetic tape
206
is reproduced by a rotary head
207
. The video data thus reproduced in the recording/playback unit
203
is subjected to an error-correction processing performed by an error correction code decoding unit
204
. The video data after the error correction is then output as video signals through a video signal decoding unit
205
.
Various types of codes are usable as the error correction code to be processed in the error correction code encoding unit
202
and the error correction code decoding unit
204
. One example of such error-correction codes is a product code which has linear-structure error-correction codes arranged both in column and line directions of a rectangular matrix of information symbols. For instance, a product code codeword as shown in
FIG. 16
is known. The product code codeword shown in
FIG. 16
has a C
1
codes (referred to also as “internal code”) which are consecutive in the direction of the magnetic tape
206
, and C
2
codes (referred to also as “external code”) which are arranged in a direction perpendicular to the direction of arrangement of the C
1
codes.
In the example of the product code codeword shown in
FIG. 16
, the C
1
code is a linear-structure error correction code which has a code length of 10 symbols and a parity number of 4 symbols and which is capable of effecting correction of up to 2 symbols at the maximum. Likewise, each C
2
code is a linear-structure error correction code which has a code length of 14 symbols and a parity number of 14 symbols and which is capable of effecting correction of up to 2 symbols at the maximum. Thus, the product code codeword is composed of elementary linear-structure error-correction codes. The sequence of encoding may be such that C
1
codes are encoded first followed by encoding of the C
2
codes or vice versa. It is known that the same encoding result is obtained regardless of the sequence of encoding.
It is assumed here that the C
2
codes are encoded first, and then the encoding of the C
1
codes is performed. In such a case, based on the definition, a symbol group
212
is a group of parity symbols of the C
1
codes. Obviously, a symbol group
213
shown in
FIG. 16
is a group of parity symbols of the C
1
codes, added to the parity symbols of the C
2
codes. Since identical encoding results are obtained regardless of the sequence of encoding as stated before, the symbol group
213
shown in
FIG. 16
also is a group of parity symbols of the C
2
codes added to the parity symbols of the C
1
codes. Thus, even when the encoding sequence is such that the encoding of the C
1
codes is performed subsequent to the encoding of the C
2
codes, not only the symbol group
211
but also the symbol group
212
are regarded as being C
2
codes, when the matrix of the symbols is viewed in the columnar direction.
It has been known that error correction ability for correcting error of a product code can be enhanced by repeating decoding a plurality of times, by making use of the above-described characteristic of parity symbols of the product code. For instance, when decoding processing is repeated such that a decoding processing of the C
1
codes in the line direction is effected first and then a decoding processing of the C
2
codes is performed in the columnar direction, errors that remain not corrected through the decoding of the C
1
codes may be corrected in the course of the decoding processing of the C
2
codes. Further repetition of the decoding processings such as decoding processing of C
1
code, decoding processing of C
2
code, and so on, serves to enhance the error correction ability without fail.
Pseudo product code, which can store two series of information symbols, is also known, as being usable as an error correction code in the error correction code encoding unit
202
an the error correction code decoding unit
204
of the circuit shown in FIG.
15
.
A pseudo product code is formed as follows. Information symbols of a first series are arranged in a rectangular matrix form, and columnar linear-structure error correction codes are formed, followed by addition of information symbols of a second series. Then, linear-structure error correction codes are formed in the line direction, on the entity composed of columnar-direction-encoded first series information code and the second series information symbols.
FIG. 17
shows an example of the pseudo product code codeword. As in the case of the product code described above, codes of the direction consecutive on a magnetic tape
207
are referred to as C
1
codes (internal codes), while the codes in the other direction are referred to as C
2
codes (external codes).
In the pseudo product code codeword shown in
FIG. 17
, a C
1
code is a linear error correction code having a code length of 12 symbols and a parity number of 4 symbols and capable of correcting up to 2 symbols at the maximum, while a C
2
code is a linear error correction code having a code length of 14 symbols, parity number of 4 symbols and capable of correcting up to 2 symbols at the maximum. Information symbols of the first series are stored in a rectangle composed of 6 symbols in the C
1
code direction and 10 symbols in the C
2
code direction. Information symbols of the second series are stored in the starting two symbols of the C
1
code information symbols. This pseudo product code is a modification of the above-described product code and, hence, is not a perfect product code.
The symbol group
222
shown in
FIG. 17
constitutes C
2
codes, but the symbol group
223
does not form C
2
codes. This is because, while the information symbols of the first series constitute both the C
2
and C
1
codes, the information symbol of the second series constitute only the C
1
codes.
In most cases, the information symbols of the second series carry information of the type which is needed prior to decoding of the C
2
code. For instance, information symbols of the second series carry position information which are necessary for arraying discontinuously-appearing C
1
codes into the form of the pseudo-product code.
The pseudo product code encoding unit, which corresponds to the error correction code encoding unit
202
of
FIG. 15
, operates to rearrange the first-series information symbols that are inputted in accordance with the direction of arrangement of the C
1
codes into the direction of arrangement of the C
2
codes, thereby encoding these information symbols into the C
2
codes, and also to add the parity symbols of the C
2
code
Hattori Masayuki
Yamamoto Kohei
Chase Shelly A
Chung Phung M.
Frommer William S.
Frommer & Lawrence & Haug LLP
Sony Corporation
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