The method has two possible transmission modes: a first mode whereby a first transmitter (1) sends frames including sufficient auxiliary data to enable a first receiver (2) to acquire frame synchronization in a reliable fashion, said auxiliary data including a synchronization pattern, a second mode in which said first transmitter sends frames including insufficient auxiliary data to enable said first receiver to acquire said frame synchronization in a reliable fashion but, by virtue of a knowledge of said frame synchronization acquired previously, in said first mode, enabling loss of frame synchronization to be determined, loss of frame synchronization by said first receiver being signalled to said first transmitter by a second transmitter (15) changing from said second transmission mode to said first transmission mode and by a second receiver (16) detecting said change of transmission mode, and said second transmitter transmitting in said second mode modified frames including no payload data sequence imitating the synchronization pattern of the first mode.