Communications transmission engineering. A digital type of phase modulation that uses an analogue carrier and a digital modulation signal with constant frequency and constant amplitude. When the modulation signal changes from the digital 0 to the digital 1 the phase of the carrier is abruptly changed for example from 0° to 180 ° and vice versa. There are several types of phase shift keying which use different numbers of phase positions for the signal coding.
The most commonly used are: Binary Phase Shift Keying (BPSK), Quadrature Phase Shift Keying (QPSK), Pi/4-Quadrature Phase Shift Keying (Pi/4 QPSK), and Offset Quadrature Phase Shift Keying (OQPSK).