BPSK in noise: reading a constellation

Wire a bit source through an AWGN channel and learn to read EVM straight off the I/Q scope.

Lorem ipsum dolor sit amet, consectetur adipiscing elit. In this tutorial you build the smallest interesting communications link — a bit source, a modulator, an additive-noise channel, and a constellation sink — then watch what noise does to the symbols.

Step 1 — drop the blocks

Nullam quis risus eget urna mollis ornare vel eu leo. Drag a Bit Source onto the canvas, then a Modulator, an AWGN Channel, and a Constellation sink. Wire them left to right.

Step 2 — sweep the SNR

Cum sociis natoque penatibus et magnis dis parturient montes, nascetur ridiculus mus. As you lower the SNR, the four clusters bloom outward; the error-vector magnitude readout climbs to match.

EVM (%) ≈ 100 · 10^(−SNR/20) for an unfiltered AWGN link.

Step 3 — read it

Vestibulum id ligula porta felis euismod semper. Once the clusters start to overlap, symbol decisions cross the axis and the bit-error rate takes off. Try the live lab below.

LIVE LAB Tune it in the page embed.potik.org/bpsk-noise