A signal process for a modulator comprising:(a) means for detecting the binary values of each pair of consecutive bits of an NRZ input signal, (b) means for generating signals having waveshapes according to the functions y1 =-A-(1-A) cos (2??t/T), y2 =-cos (??t/T), y3 =cos (??t/T) and y4 =A+(1-A) cos (2t/T), where T is the input signal symbol duration, and A is an amplitude parameter, (c) means fo