Modulation Lab

Data Communication, Lecture 7. Put bits on a carrier wave with ASK, FSK and PSK, build 4-QAM and 8-QAM signals step by step, and see why more points need a cleaner channel.

Bits (top) and modulated carriers · dashed lines = bit boundaries

Change one property of the carrier

ASK: 1 = carrier on, 0 = off (OOK). BFSK: 1 = higher frequency f₁, 0 = lower f₀. BPSK: 1 = phase 0°, 0 = phase 180°.

Constellation
Modulated signal, one symbol per segment

Bits → groups → points → signal

Bits per symbol log₂LBaud rate S = N / log₂LBandwidth B = (1 + d)S, d = 0

Received points with noise · grid lines = decision boundaries · orange = decided wrongly

How many points can the channel support?

Symbols sent600Symbol errorsBits per symbol

Wi-Fi does exactly this: close to the router it uses many points (more bits per symbol); far away, where SNR is low, it falls back to fewer.