Method of maximum likelihood decoding with sub-sampled decoding trellis, and corresponding decoding device

A method for the maximum likelihood decoding of a sequence of samples corresponding to the convolutional coding of a sequence of digital source elements, of the type implementing a Viterbi algorithm type of decision algorithm, defining an initial decoding trellis, constituted by a set of nodes corresponding to the possible states of the coding, each node being connected to its most probable direct antecedent node, and consisting in making a trace-back of an optimum path in said trellis, said method comprising the following steps:

• sub-sampling, by a ratio p, of said initial trellis, consisting in preserving only the nodes corresponding to one sample out of p consecutive samples and in associating, with each of the nodes preserved, an information element identifying its p order antecedent node in said initial trellis,
• the trace-back of an optimum path in the sub-sampled trellis, by the association, with each node considered, of the p order antecedent node, delivering an information element designating the last two nodes of said optimum path,
• over-sampling by a ratio p by association, with said information element designating the last two nodes of said optimum path, of a decoding sequence corresponding to said last two nodes as well as to all the p-1 intermediate nodes not preserved during said sub-sampling step, p being an integer strictly greater than 1, chosen so that there is a single path between a node and its p order antecedent in said initial trellis.