An adaptive signal processing method to achieve an increase in capacity of data transfer systems, in which control data is returned via a backward channel. The method provides signal processing using an electrical sub-carrier sub-division according to frequency, the electrical sub-carrier with the lowest carrier frequency being permanently used as the backward channel (RC) for transferring control information relating to the current transfer quality of each sub-carrier. An electrical modulation on N parallel sub-carriers takes place in the transmitter (Tx) and then an optical intensity modulation is carried out for a serial data transfer in the optical channel (IRWC). The discrete division of the information to be transferred to the sub-carriers in a real-time operation can take place by the implementation of specific bit-loading algorithms.