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QAM Constellation

Quadrature Amplitude Modulation - combining amplitude and phase

20 dB

16-QAM Ideal Constellation

Received Symbols with AWGN

4
Bits/Symbol
16
Constellation Points
0.47
Min Distance (norm)
~10⁻⁴
Est. Symbol Error

Understanding QAM

Higher Order = More Bits: 16-QAM carries 4 bits/symbol, 64-QAM carries 6 bits/symbol, 256-QAM carries 8 bits/symbol.

Trade-off: More constellation points means higher throughput but requires better SNR to distinguish symbols.

Gray Coding: Adjacent symbols differ by only 1 bit to minimize bit errors from symbol errors.

Applications: Wi-Fi (up to 1024-QAM), cable modems, LTE, digital TV.