Q. Explain phase-shift keying?

In PSK, the phase angle of a carrier is keyed between two values. When the values are separated by π radians, it is known as phase-reversal keying (PRK). The PSK waveform in the bit interval is given by

Equation can be viewed as a carrier Ac cos(ωct + φc) modulated in amplitude by a digital signal d(t) with amplitudes of 1 when the binary digit in the bit interval is 1 and 0, respectively. Figure illustrates the functions of a coherent PSK communication system, which is similar to the ASK system of Figure with the following differences:

• The received signal is now given by

• A gain of 2 is assigned to the integrator.
• A threshold is absent when binary digits 0 and 1 occur with equal probability.

No truly noncoherent PSK version is possible because the PSK signal carries its information in the carrier's phase, whereas a noncoherent system purposely disregards phase and operates only on signal amplitude.