The digital symbols of a sequence are assigned to respective positions in successive timeslots, according to a predetermined slot format. In a plurality of timeslots, a symbol of the sequence is replaced by a substitution symbol carrying additional information. A signal representing the sequence of symbols, which is divided into the timeslots, is transmitted on a communication channel. The production of the sequence includes an interleaving having an interleaving period longer than a timeslot, generally performed after a channel coding. The position of the substitution symbols in the timeslots which include them is varied, in order to optimize the performances of the transmission chain.