A method for modulating and demodulating PSK signals characterized by comprising: - encoding in a symbol of two bits a type of transition techniquewhich is used on a BPSK input signal for BPSK modulation and selected from: direct multiplication which is multiplying the BPSK input signal by a modulating message, constant envelope with positive frequency shift and constant envelope with negative frequency shift, wherein both constant envelope with frequency shift techniques keep the amplitude of the BPSK input signal constant and change the phase of the BPSK input signal, by increasing the frequency of the BPSK input signal for the constant envelope with positive frequency shift and decreasing the frequency of the BPSK input signal for the constant envelope with negative frequency shift, the phase change of the BPSK input signal being determined by the value of the two bits symbol; - encoding in a symbol of four bits a type of transition technique which is used on a QPSK input signal for QPSK modulation, wherein two bits of the four bits symbol encode a first type of transition technique used for BPSK modulation as explained above on an I-branch BPSK signal, and the remaining two bits of the four bits symbol encode a second type of transition technique used for BPSK modulation on a Q-branch BPSK signal, the first and second type of transition technique defining the type of transition technique used on the QPSK input signal and both being selected from direct multiplication, constant envelope with positive frequency shift and constant envelope with negative frequency shift. - encoding in a symbol of two bits a type of transition techniquewhich is used on a BPSK input signal for BPSK modulation and selected from: direct multiplication which is multiplying the BPSK input signal by a modulating message, constant envelope with positive frequency shift and constant envelope with negative frequency shift, wherein both constant envelope with frequency shift techniques keep the amplitude of the BPSK input signal constant and change the phase of the BPSK input signal, by increasing the frequency of the BPSK input signal for the constant envelope with positive frequency shift and decreasing the frequency of the BPSK input signal for the constant envelope with negative frequency shift, the phase change of the BPSK input signal being determined by the value of the two bits symbol; direct multiplication which is multiplying the BPSK input signal by a modulating message, constant envelope with positive frequency shift and constant envelope with negative frequency shift, wherein both constant envelope with frequency shift techniques keep the amplitude of the BPSK input signal constant and change the phase of the BPSK input signal, by increasing the frequency of the BPSK input signal for the constant envelope with positive frequency shift and decreasing the frequency of the BPSK input signal for the constant envelope with negative frequency shift, the phase change of the BPSK input signal being determined by the value of the two bits symbol; - encoding in a symbol of four bits a type of transition technique which is used on a QPSK input signal for QPSK modulation, wherein two bits of the four bits symbol encode a first type of transition technique used for BPSK modulation as explained above on an I-branch BPSK signal, and the remaining two bits of the four bits symbol encode a second type of transition technique used for BPSK modulation on a Q-branch BPSK signal, the first and second type of transition technique defining the type of transition technique used on the QPSK input signal and both being selected from direct multiplication, constant envelope with positive frequency shift and constant envelope with negative frequency shift.