The invention relates to signal transmission. The use of the invention for transmitting and receiving quadrature amplitude modulation signals on unlicensed frequency bands makes it possible to lower a demodulation threshold owing to a low synchronization threshold. The inventive method consists in extending a burst of M m-level quadrature amplitude modulation signals with the aid of two pseudo-random sequences, one of which is periodically inverted in some bursts, thereby making it possible to extract, on a receiving side, the quadrature amplitude modulation signal components corresponding to a meander signal of the pseudo-random sequence inversion (the frequency of which is known). The inventive method is carried out by means of a corresponding system in a hardware and software mode. Moreover, said method can be used for synchronizing the reception of quadrature amplitude modulation signals.