Digital Modulation

ASK, FSK, PSK and QAM map bits onto carrier amplitude, frequency and phase.

Intermediate

ASK / OOK — switch the carrier on and off (cheap 433 MHz remotes).
FSK / GFSK — two or more frequencies (Bluetooth LE, LoRa uses chirp spread spectrum).
PSK — shift the phase: BPSK (1 bit/symbol), QPSK (2 bits/symbol).
QAM — vary amplitude and phase together; 16-QAM = 4 bits/symbol, 256-QAM = 8 bits/symbol (Wi-Fi, 4G/5G, cable).

Higher-order schemes pack more bits per symbol but need a higher SNR. Results are visualised on a constellation diagram, and quality is measured by bit error rate (BER).

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