Description
The (Short-Time) Fourier Transform converts a time-domain CSI window into a frequency-domain or time-frequency representation. STFT is the standard front-end for Doppler / micro-Doppler analysis: each subcarrier's amplitude or phase time-series turns into a 2D spectrogram that feeds CNN/Transformer backbones. FFT-based features are nearly free to compute and dominate WiFi-radar pipelines.
When it's used
- STFT spectrograms feeding HAR / gesture classifiers
- Doppler-bin extraction for
crowd-flow-estimation - Subcarrier-correlation analysis in the frequency domain
Limitations
- Time-frequency resolution trade-off is fundamental
- Window length / overlap choice affects downstream accuracy
- Phase wrap obscures direction of motion in raw STFT phase