Error detection method using CRC

Details Error detection method using CRC Error detection method using CRC

1991-11-12

1994-08-23

Nguyen, Hoa T.

Excavating

371 30, 371 401, 371 403, G06F 1110

Patent

active

053413849

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

1. Field of the Invention
The present invention relates to an error detection method which is applied to e.g. digital communication.
2. Description of the Related Art
FIG. 3 is a flowchart for explaining the prior art error detection. As seen from FIG. 3, on a transmission side, speech is inputted (Step 14) and the speech is encoded (Step 15). The information (a bits) thus obtained is supplemented with an error detection code CRC (cyclic redundancy check code) (b bits) (Step 16). The information of (a+b) bits is encoded with an error correction code (Step 17) to be transmitted as one frame data (Step 18).
On a receiving side, the above error correction code is decoded (Step 20) and subjected to a CRC checking (Step 21) to detect an error (Step 22). Data having no error detected in the checking is subjected to a speech decoding processing on the decoded data (Step 23). The data with some error bits detected is subjected to sound processing, such as interpolation, using a previous frame or muting in place of the above speech decoding (Step 24). Both outputs are synthesized to be outputted as speech (Step 25).
However, in the above prior art error detection method, the CRC cannot detect the error in the case where one or more error bits are included in (a+b) bits. Thus, the prior art error detection method cannot provide error detection with high accuracy.
For example, when assuming a generator polynomial G (x) represented by
Then the above e(x) can be transformed into detect e(x) as a correct pattern. Therefore, although the error as many as 4 (four) bits is included in (a+b) bits, the error detection cannot be made.
The present invention intends to solve the above conventional problem, and an object of the present invention is to provide an excellent error detection method which can surely detect the error for the data including the error pattern as mentioned above.


DISCLOSURE OF THE INVENTION

In order to attain the above object, a CRC and an error correction code are selected so as to satisfy the following condition overlooked by the error detection code (CRC) although some error bits is included in (a+b) bits, and Mmax represents the error detection capability (the number of error bits which can be surely detected) of the error correction code. In the above case of G(x)=1+x+x.sup.2 +x.sup.4 +x.sup.5 +x.sup.7 Kmin=4 so that CRC is combined with the error correction code satisfying Mmax.ltoreq.4. Further, the error detection in decoding the error correction code as well as the above CRC checking is given to the error detection method. If an error has been detected in decoding the error correction code or in the CRC checking, it is decided that an error is included in the above a bits. Thus, the corresponding frame including the a bits is interpolated or sound reproduced from the frame is muted. Thus, the probability of outputting the speech obtained by decoding data which includes the error can be greatly reduced.
The present invention has the following advantage in the construction described above. If an error is detected in decoding the error correction code, it is decided that the error is included in the a bits. Therefore, the error which cannot be detected by the CRC checking can be surely detected. Thus, in accordance with the present invention, the probability of outputting the speech obtained by decoding the data as it includes the error can be greatly reduced.


BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flowchart for explaining the error detection method according to one embodiment of the present invention;
FIGS. 2A and 2B are views showing exemplary combinations of an error detection code (CRC) and an error correction code in the error detection method; and
FIG. 3 is a flowchart for explaining the prior art error detection method.


DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 is a flowchart in the case where the error detection method according to one embodiment of the present invention is applied to decoding of encoded speech data. As seen from FIG. 1, on

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Hideki Imai, "Theory of Codes", pp. 106 and 107, Electronics Information Communication Committee.

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