A method and apparatus are provided for modulating a binary source sequence including of a plurality of source words to generate modulated symbols. The method implements error-correction encoding of the plurality of source words, implementing one or more encoding modules, each implementing a separate error-correction code to generate a plurality of code words, the source words being encoded in series. The code words are interlaced to generate an interlaced sequence. The interlaced sequence is differentially modulated to generate modulated symbols. Each code word is broken down into at least one group with a number of bits equal to the base-2 logarithm of a number of states of a modulation implemented by the step of differentially modulating. The interlacing step distributes the groups such that two adjacent groups in the interlaced sequence belong to separate code words.