Patent FR-2807895-A1 (FR)
Title: Methods and devices for coding and decoding and systems implementing them, for use in protected wireless communications
Inventor: LE DANTEC CLAUDE
IPC: H04L1/00
Filed: 2000-04-18
Abstract: The method for coding a source sequence (u) to obtain a coded sequence, comprises the following steps: the first operation of division, in block (508), of the source sequence (u) into p1 first sub-sequences (Ui), where p1 is a positive integer, and the coding of each sub-sequence by the first method of circular convolutive coding; the operation of interfacing, in block (506), to obtain an interlaced sequence (u asterisk ); and the second operation of division, in block (507), of the interlaced sequence (u asterisk ) into p2 second sub-sequences (U'i), where p2 is a positive integer, by the second method of circular convolutive coding. At least one of the integers, p1 and p2 is strictly greater than 1, and at least one of the first sub-sequences (Ui) is not interlaced of the second sub-sequences (U'i).  The first or second method of circular convolutive coding includes a step of pre-coding in order to define the initial state of cooling for considered sub-sequences, in a manner to produce a pre-coded sequence. Simultaneously with the pre-coding of one of the first sub-sequences (Ui), the circular convolutive coding or other first sub-sequence (Uj) is effected. The integers p1 and p2 are equal, the size of all sub-sequences is identical, and the first and second methods of circular convolutive coding are identical. The coding method comprises a supplementary interlace operation for a parity sequence (v1), which results from the first operation of division into sub-sequences and coding, and the third operation of divisions into sub-sequences and coding, which consists of dividing the interlaced sequence into p3 third sequencecs (U''i), where p3 is a positive integer, and the coding of each third sub-sequence by the third method of circular convolutive coding. The coding device contains the means for dividing and coding the source sequence into sub-sequences, the means for interlacing the source sequence, and the means for dividing and coding the interlaced source sequence, and the means for coding the second sub-sequences by the second means of circular convolutive coding. The coding dvice comprises the means for supplementary interlacing for the parity sequence, and the third means of division into sub-sequences and coding of the interlaced sequence. The decoding method, utilizing a turbodecoding, includes the following iteratively effected steps: the first operation of division into sub-sequences applied to the received symbols representative of the source sequence (u) and the first parity sequence (v1), and also a priori information on the source sequence; the first operation of elementary decoding for each triplet of sub-sequences, for decoding by a circular convolutive code and providing a sub-sequence of extrinsic information on a sub-sequence of the source sequence; the interlace operation of the sequence formed of sub-sequences of extrensic information, the second operation of division into sub-sequences applied to the symbol representative of the interlaced source sequence and the second parity sequence, as well as a priori information on the interlaced sequence, the second operation of elementary decoding for each triplet of sub-sequences, for decoding by a convolutive circular code and providing a sub-sequence of extrensic information, and the operation of de-interlacing of the sequence formed of sub-sequences of extrensic information. The means for division into sub-sequences, for elementary decoding, interlacing, and de-interlacing are operated iteratively. The apparatus for processing digital signals contains the means adapted to implement the coding method and/or decoding method, the coding device and/or decoding device. The telecommunication network comprises the means adapted to implement the coding method and/or decoding method, the coding device and/or decoding device. A mobile station in telecommunication network contains the means adapted to implement the coding method and/or decoding method, the coding device and/or decoding device. A device for processing signals representative of word contains the coding device and/or decoding device. A device for data transmission contains a transmitter adapted to implement a protocol of transmission in packets, and contains the coding device and/or decoding device, and/or the device for signal processing. The protocol is of the Asynchronous Transfer Mode (ATM) type, or the Internet Protocol (IP) type.