The disclosure relates to a cellular radiotelephone signal of the type comprising, a principal bidirectional symmetrical channel, comprising a principal uplink path and a principal downlink path, particularly to guarantee transmission of data at low or medium rate and of the signalling information and commands, at least one auxiliary channel working only in the downlink sense, particularly to guarantee the data transmission at high rates, using a multi-carrier technique which gives a distribution of data over time and frequency, with a sub-frame structure. The beginning of at least one sub-frame in the supplemental channel is offset by a time interval of fixed duration which is not zero (Δt) with relation to a determined time (t0), fixed in the principal channel, such as to permit a synchronization at the sub-frame level of the supplementary channel in a terminal, by instantaneous detection of said determined time (t0) and addition of said time interval (Δt).