Error detection/correction and fault detection/recovery – Pulse or data error handling – Digital data error correction
Patent
1997-07-21
2000-03-28
Grant, William
Error detection/correction and fault detection/recovery
Pulse or data error handling
Digital data error correction
714785, 714759, 714755, H03M 1300, H03M 100, G06F 1110
Patent
active
060444827
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present application is concerned with the transmission of data using forward error correction, that is, where data are encoded using a redundant code such that, upon reception in the presence of errors, the fact that errors have occurred can be recognised at a receiver, and preferably (up to a maximum tolerable error rate) corrected.
The context particularly addressed is where a requirement exists to transmit also auxiliary data also requiring a high level of error protection.
2. Related Art
Error correction coding techniques of many different types have long been used. Some, such as represented by U.S. Pat. No. 5,003,539 (WO,A,87 06368) even use two levels of coding to cause error correction coding to carry additional data. Others use only one level (e.g., U.S. Pat. Nos. 4,271,529 and 3,466,601). Other coding/decoding techniques for conveying extra signalling capacity are also known (e.g., WO,A,93 12598).
SUMMARY OF THE INVENTION
According to one aspect of the invention there is provided an apparatus for decoding data which has been coded by coding first data in accordance with a first redundant code to produce first coded bits, coding second data in accordance with a second redundant code to produce second coded bits, and adding the second coded bits to the first coded bits, the apparatus comprising: code a plurality of error values each corresponding to the assumption that the second coded bits constitute a respective one of a plurality of allowed codewords of the second code; which corresponds to the smallest error value; codeword to produce modified data; and code.
Preferably the first code is a systematic code so that the first coded bits comprise the fit data bits and parity bits, the second coded bits being added only to the parity bits, and the means operable to determine error values comprises the first code; and redundant code, the error value being the Hamming distance between the codeword and the syndrome.
In another aspect of the invention there is provided an apparatus for coding data for transmission comprising: in accordance with a first redundant code to produce first coded bits for transmission; in accordance with a second redundant code to produce second coded bits for transmission;
BRIEF DESCRIPTION OF THE DRAWINGS
Some embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings, in which:
FIG. 1 is a block diagram of one form of data coding apparatus according to the invention; and
FIG. 2 is a corresponding decoder.
DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS
This example supposes that, for each successive data frame of 96 bits each, a requirement exists to transmit 51 data bits, and that these bits are to be coded using a (96, 51) burst error correcting cyclic code. This is a systematic code--i.e. the data bits themselves are unchanged by the coding, so that it requires the transmission of 51 data bits plus 45 parity bits. Its generator polynomial is x.sup.45 +x.sup.40 +x.sup.35 +x.sup.25 +x.sup.20 +x.sup.5 +1. Such codes are conventional, as is their decoding using error-correction techniques.
Thus in FIG. 1, user data input at an input 1 are formatted in a framing unit 2 into groups of 51 bits which are supplied to a coder 3 for the cyclic code to generate 45 parity bits. As shown, the data and parity bits are assembled in a register 4. For clarity, internal data paths in the apparatus of FIG. 1 are shown as parallel connections, but the signals may be processed sequentially using standard digital signal processing techniques, if desired.
It is supposed, further, that there is a requirement to transmit auxiliary data, for example for control of remote equipment such as a modem, and that eleven such control words are desired, with a heavy level of error protection so that they may be recognised correctly at a receiver in the presence of transmission errors. In addition, no further transmission capacity is available over and above the 96 bits already mentioned.
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British Telecommunications public limited company
Calcano Ivan
Grant William
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