1. Field of the Invention
The present invention relates to the transmission of data, and in particular to the transmission of digital data coded by means of a turbocoder.
2. Discussion of the Related Art
A turbocoder includes two (or more than two) simple convolutional type coding circuits and one or several inter-leavers operating on large data blocks (typically, from 100 to 16,000 bits).
FIG. 1 illustrates a conventional four-state convolutional type coder. Coder 1 receives, at each pulse of a clock, not shown, a bit D. Bit D belongs to a bit sequence corresponding to data to be transmitted, digitized and arranged in series.
Data bit D is directly provided at the output of coder 1 by a first branch 11. Bit D is provided to a coding circuit C by a second branch 12. Circuit C outputs a so-called redundancy bit Y.
Circuit C includes four D-type flip-flops Bi (B0, B1, B2, B3) connected in series and five adders 2i (20, 21, 22, 23, and 24). Adders 2i are adders modulo 2. At each clock pulse, the state (“0” or “1”) at the input of a flip-flop Bi is transferred to its output. Adders 2i are coupled to elements of coder 1 (input, flip-flops Bi, other adders, output) so that redundancy bit Y represents a linear combination of four successive data bits.