there are three types of modulation =>
i. frequency modulation - it is widely used for a variety of radio communications applications. it changes the frequency of the carrier a/c to signal information.
ii. phase modulation - it is most commonly used to convey digital signals. All high performance modems today use phase modulation. form of modulation that represents information as variations in the instantaneous phase of a carrier wave.
iii. amplitude modulation - is a technique used in electronic communication, most commonly for transmitting information via a radio carrier wave in which the amplitude of a carrier wave is varied in accordance with some characteristic of the modulating signal.