Constellation diagram examples

1. What does a constellation diagram show?
2. Why are constellation diagrams used?
3. What is QPSK constellation diagram?

What does a constellation diagram show?

The constellation diagram shows all the possible symbols that can be transmitted by the system as a collection of points. In a frequency or phase modulated signal, the signal amplitude is constant, so the points lie on a circle around the origin.

Why are constellation diagrams used?

The constellation diagram is useful because it displays both the ideal (reference) signal and the actual measured signal on the same plot. The ideal signal locations of a constellation diagram are pre-defined generically depending on the modulation format chosen.

What is QPSK constellation diagram?

QPSK uses four points on the constellation diagram, equispaced around a circle. With four phases, QPSK can encode two bits per symbol, shown in the diagram with Gray coding to minimize the bit error rate (BER) – sometimes misperceived as twice the BER of BPSK.