Plot of symbol points showing modulation and noise effects.
A constellation plots possible symbol points in the I-Q plane. Noise scatters received points around ideal positions; distance between points sets error probability. EVM measures quality. Constellation reveals distortions: phase noise, I/Q imbalance, compression.
64-QAM has 64 points arranged in an 8×8 grid.
Constellation diagrams show the symbol points of a digital modulation, which gives an immediate picture of the quality of a link.
Plot of symbol points showing modulation and noise effects.
Constellation diagrams show the symbol points of a digital modulation, which gives an immediate picture of the quality of a link.
The received symbols are clustered near their ideal points, which indicates a high SNR and low distortion.
Phase or frequency offset and noise, which often point to synchronisation problems or interference.
Typical applications include checking whether the symbols of a receiver are tight enough after an equaliser, diagnosing phase noise from a spread constellation and comparing two modulation formats by their point spacing.
Study "Digital modulation" first (topic 80 of 101 in Signals, Control & Comms). It covers the groundwork this topic builds on.
I/Q components. Gray coding. Decision boundaries.
64-QAM has 64 points arranged in an 8×8 grid.
The next topic is "Bit error rate", which builds directly on this one.
It is classed as Advanced in Signals, Control & Comms (topic 81 of 101). It is an advanced topic. It assumes you are comfortable with the intermediate topics in Signals, Control & Comms.
Want to practise? Open the interactive course for quick checks, quizzes, simulations and progress tracking.