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Codes for Correction of Two or Three Errors and Detection of All Unidirectional Errors

IP.com Disclosure Number: IPCOM000035184D
Original Publication Date: 1989-Jun-01
Included in the Prior Art Database: 2005-Jan-28
Document File: 2 page(s) / 23K

Publishing Venue

IBM

Related People

Blaum, M: AUTHOR [+2]

Abstract

A method is described for constructing a multibit error-correction/all unidirectional error-detection (EC/AUED) code, wherein k information bits are first encoded into a systematic [n', k, 2t+1] EC code, and r* bits are appended therein to enable AUED capability, the extra r* bits being a function of the weight of the codeword of length n' and are obtained through a table look-up.

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Codes for Correction of Two or Three Errors and Detection of All Unidirectional Errors

A method is described for constructing a multibit error-correction/all unidirectional error-detection (EC/AUED) code, wherein k information bits are first encoded into a systematic [n', k, 2t+1] EC code, and r* bits are appended therein to enable AUED capability, the extra r* bits being a function of the weight of the codeword of length n' and are obtained through a table look-up.

By way of example, let t=2, k=4. The shortest [n', 7, 5] code that exists has n'=15, which is the 2-error correcting BCH code of length 15. A stream of 7 input bits is first encoded into the BCH code which adds 8 redundant bits. The weight of these 15 bits is then determined as a 4-bit binary number. This 4-bit binary number is then used for looking up a tail matrix table (Table I) where the assignment of a 6-bit vector output is obtained. This 6-bit vector is then appended to the encoded 15-bit vector, completing the encoding.

In decoding, a received data stream C0 C1 ... C20 is sent to a separator which takes the first 15 bits and sends them to a BCH decoder. If this BCH decoder is unable to make an estimate, a flag is raised to indicate that more than two unidirectional errors have been detected. If an estimate can be made, the BCH decoder gives a vector C' = C0 C1 14 . The weight of C' is then estimated and sent to the look-up table to obtain its tail C15 C16 ... C20 . The result from the table lo...