This wave has a period of *p*, noted above. Also notice
that the start of the wave's period 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 (1).

So what's the point? 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):

Bit value |
Amount of shift |

00 | None |

01 | 1/4 |

10 | 1/2 |

11 | 3/4 |

This technique of letting each shift of a wave represent some
bit value is **phase shift keying**. *But* the real
key is to shift each wave *relative to the wave that came
before it*. Above is an example.
*Please note that I just randomly chose binary vales for
each wave, and that the values shown are not correct!*.
The correct pattern should be: 00 00 10 00 10 00.