Described is a method and system for increasing the spectrum efficiency in a radio transmission system. Advantageously, the interference phenomenon is used for transmitting two different signals, by utilizing for each of them carriers at the same frequency, thus obtaining in this way a doubling of the spectrum efficiency. Practically, the same signal is transmitted by two different antennas in order to have two coherent signal sources. On the receiving front, there are points of maximum and minimum of this signal. If the original signal is properly phase shifted with an antenna vis--vis the other one, the effect will be to arrange the maxima and minima on the receiving front in a corresponding way. The present invention allows for the use of dual polarization antennas (H and V or any other type of orthogonal polarization) to obtain a still higher spectrum efficiency.