The invention relates to a method for dividing the bit rate of QPSK signals by splitting the spectrum of said QPSK signals into at least two channels having band-limited filters in the modulator and demodulator. The prefiltered QPSK signal is split into at least one real and at least one imaginary spectrum at the transmitter end, is transmitted in frequency multiplex, and the filters in the modulator of the transmitter and the demodulator of the receiver are dimensioned according to the transmission function.