Error detection/correction and fault detection/recovery – Pulse or data error handling – Digital data error correction
Patent
1998-04-19
2000-09-12
Decady, Albert
Error detection/correction and fault detection/recovery
Pulse or data error handling
Digital data error correction
H03M 1303
Patent
active
061192643
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The field of the invention is that of the encoding of digital data and especially source data organized in blocks of data, or messages, that are independent of one another and have to be encoded and decoded on a unit basis.
More specifically, the invention relates to a method and device of convolutive type error-correcting encoding adapted to the constraints laid down by the transmission of messages and especially short messages (for example of about some tens or some hundreds of bits). The invention also relates to a decoding method and device adapted to the encoding method of the invention.
The invention can be applied in all cases where it is necessary to transmit digital information with a certain degree of reliability. A preferred field of application of the invention is that of digital transmission on highly noise-infested channels. For example, the invention can be implemented for the transmission and reception of signals by satellite. In particular, the invention can be used for communications with orbiting satellites. Indeed, in systems that implement such satellites, communications can only take place in very short data bursts, when the satellites are in the axis of the terrestrial antenna.
The invention can also be advantageously used for space transmissions towards or between space vehicles and/or space probes and in all cases where the reliability of the decoding is of vital importance.
More generally, however, the invention can be applied in the same way to all types of transmission, by RF channels or by cable. In particular, it can be used for digital radiocommunications systems such as the GSM system. Another possible application is that of data transmission on computer networks and especially on the Internet.
Any digital signal, whatever its origin, may be encoded and decoded according to the invention provided that it is organized in blocks of fixed size.
2. Description of the Prior Art
It is known that convolutive encoders are particularly efficient in terms of error correction quality. It will be recalled that, in general, the convolutive codes are codes that associate at least one encoded data element with each source data element to be encoded, this encoded data element being obtained by the modulo 2 summation of this source data element with at least one of the previous source data elements. Thus each encoded symbol is a linear combination of the source data element to be encoded and the previous source data elements taken into account.
In the decoder, the original data elements are most usually reconstructed by means of a maximum likelihood algorithm, for example the Viterbi algorithm, whose decisions may, if necessary, be weighted. This algorithm takes account of a sequence of received encoded symbols to give an estimation of each encoded data element at transmission in determining the source sequence that most probably corresponds to the received sequence.
Among the convolutive codes, there is a very advantageous technique known as the "turbo-code". Turbo-codes are described in particular in the European patent document EP-92 460013.3 entitled "Procede de codage correcteur d'erreurs a au moins deux encodages convolutifs systematiques en parallele, Procede de decodage iteratif, module de decodage et decodeur correspondents" (Method of error correcting-encoding with at least two systematic convolutive encodings in parallel, iterative decoding method and corresponding decoding module and decoder), and in the article by C. Berrou, A. Glavieux and P. Thitimajshima, "Near Shannon limit error-correcting coding and decoding: `turbo-codes`", Proceedings of IEEE ICC '93, Geneva, pp. 1064-1070, May 1993.
Turbo-codes are quasi-optimal binary correcting codes inasmuch as their corrective capacity is close to the theoretical limit predicted by Shannon in 1947.
A turbo-code is built out of a parallel concatenation of recursive systematic convolutive (CSR) codes coupled by a non-uniform interleaving.
The decoding, which cannot be comprehensiv
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Berrou Claude
Jezequel Michel
Chase Shelly A
De'cady Albert
France Telecom & Telediffusion de France S.A.
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