The main advantage of phase shift keying is that it allows data to be carried along a radio communications signal much more efficiently than with frequent shift keying. PSK is a digital modulation scheme that transports data by changing the phase of the carrier wave.
There are several variations of PSK. Each variation has its own advantages and disadvantages, which enable designers to choose the best one for the particular application they are working on. Quadrature phase shift keying is another form of data transport where four phase states are used, all within 90 degrees of one another.