Phase modulation (PM) is the encoding of information into a carrier wave by variation of its phase in accordance with an input signal.
Note that phase modulation can be regarded as a special case of frequency modulation where the carrier frequency modulation is the time derivative of the PM modulating signal.
Phase modulation can also be regarded as a special case of quadrature amplitude modulation.
Phase shift keying refers to the simple case of phase modulation by a simple signal with only two states, such as in morse code or radio-teletype applications.
- modulation for a list of other modulation techniques