Phase Shift Keying

Phase shift keying is a technique which shifts the period (cycle starting position) of a wave.

This wave has a period of p, noted above. Also notice that the start of the wave's cycle is at 0.

This is the same wave as the first, but its phase has been shifted. Notice that the period starts at the wave's highest point (i.e. it's Amplitude=1).

It just so happens that we have shifted this wave by one quarter of the wave's full period. We can shift it another quarter, if we wanted to, so the original wave would be shifted by half it's period. And we could do it one more time, so that it would be shifted three quarters of it's original period.

This means we have 4 separate waves. So why not let each wave stand for some binary value? Since there are 4, we can let each wave signify 2 bits (00, 01, 10, 11):

This technique of letting each shift of a wave represent some bit value is phase shift keying. Note the phase shift for each succeeding wave is relative to the wave that came before it. Above is an example.