Phase-shift keying (PSK) is a modulation process whereby the input signal, a binary PCM waveform, shifts

the phase of the output waveform to one of a fixed number of states. The demodulation process can be divided into three major subsections, as shown by Figure 4. First, since

the incoming waveform is suppressed carrier in nature, coherent detection is required. The methods by

which a phase-coherent carrier is derived from the incoming signal are termed, carrier recovery, and will be

covered first.