See also: * modulation for other examples of modulation techniques |
Alternately, this can be regarded (using complex number notation) as simple amplitude modulation of a complex-valued carrier wave by a single complex-valued signal.
Phase modulation can also be regarded as a special case of quadrature amplitude modulation, where the amplitude of the modulating signal is constant, with only the phase varying. This can also be extended to frequency modulation, as this can be regarded as a special case of phase modulation.
QAM is used extensively in modems, and other forms of digital communication over analog channels.
In these applications, the modulating signal is generally quantised in both its in-phase and 90° components. The set of possible combinations of amplitudes, as shown on an x-y plot, is a pattern of dots known as a QAM constellation.
See also: