Process for transmitting information bits with error correction coding and decoder for the implementation of this process

DETAILED DESCRIPTION The invention therefore proposes in a process of the type indicated in the introduction, that the first binary matrix comprises, in addition to the information bits, a set of bits with values a priori known to the receiver, which are distributed in an approximately uniform manner according to each dimension of the first binary matrix, which, after systematic coding, are located in determined positions of the said second binary matrix, and which are not transmitted towards the channel, and that the receiver places in the input matrix, in positions corresponding to the said determined positions of the second binary matrix, samples the signs of which correspond respectively to the a priori known values of the bits of the said set and the absolute values of which are representative of a maximum confidence.
The invention makes use of a technique similar to shortening techniques which are well known in the field of simple block codes.
Let n, k and d be the product code parameters, in the form: ##EQU1## where L is the number of elementary codes the respective parameters of which are (n.
sub.
i, k.
sub.
i, d.
sub.
i) (the case where L=2 is considered below, without limiting generality).
k and n are the respective numbers of bits in the "first" and "second" binary matrices.
The invention allows the number of independent information bits contained in the matrix to be adapted to any number k-X less than or equal to k, the receiver decoding circuit being the same whatever the number X of a priori known bits.
The positions of these X bits are uniformly distrubted in the first matrix, which allows optimum usage of the performance of the iterative decoding process.
On this point, it should be noted that a shortening of one or more codes into elementary blocks would be less advantageous as it would allow less choice in the value of X, and especially as it would lead to certain elementary decodings resulting in no BER gain.
The parameters (n',k',d') of the shortened product code are finally n'=n-X, k'=k-X and d'=d