This is normally accomplished by generating a wave in the receiver at the carrier frequency. Its principal application is also in radio, where it offers increased noise immunity and decreased distortion over the AM transmissions at the expense of greatly increased bandwidth. The two methods are very similar in the sense that any attempt to shift the frequency or phase is accomplished by a change in the other. 5 Pulse Modulation Pulse modulation involves modulating a carrier that is a train of regularly recurrent pulses. Although PCM transmits digital instead of analog signals, the modulating wave is continuous.
Digital modulation begins with a digital modulating signal.
The Columbia Encyclopedia, Sixth Edition.