Lab 3 — QPSK → Constellation → Impairments¶

Lab 3 introduces digital modulation and visualization through constellation diagrams.

Goal¶

bitstream → QPSK modulation → RF transmission → IQ capture → constellation → quality metrics

Experiment flow¶

flowchart LR
    SRC["Bitstream"]
    MOD["QPSK modulator"]
    TX["Zynq + AD9363"]
    RX["RTL-SDR"]
    IQ["IQ recording"]
    CONST["Constellation plot"]
    METRICS["EVM / phase noise"]

    SRC --> MOD --> TX --> RX --> IQ --> CONST --> METRICS

Typical impairments¶

Impairment	Visual effect
Noise	cloud spreading
Phase offset	rotation
CFO	slow rotation over time
IQ imbalance	ellipse
Clipping	distorted clusters

Demo figure¶

QPSK constellation

Engineering takeaway¶

Constellation is a compact representation of multiple impairments at once. It is one of the most powerful diagnostic tools in SDR.