Also known as: GFSK, Gaussian FSK

GFSK (Gaussian frequency-shift keying) is frequency-shift keying in which the data is passed through a Gaussian filter before it shifts the carrier, rounding off the otherwise abrupt frequency steps.¹ This smoothing narrows the transmitted spectrum, so GFSK fits more signals into less bandwidth.

A Gaussian filter rounds the frequency transitions, narrowing the spectrum at a small cost in detectability.

Overview

GFSK is closely related to GMSK (a special case with a particular modulation index). It is widely used where spectral efficiency matters at low cost — AIS marine transponders, Bluetooth, and many ISM-band radios.

Relevance

For SDR decoding, GFSK is handled like other FSK with a matched filter tuned to the Gaussian pulse shape, followed by symbol-timing recovery.

Sources

1. Frequency-shift keying — Gaussian frequency-shift keying — Wikipedia, for the Gaussian-filtered FSK definition. ↩

See also

• Frequency-shift keying (FSK)
• GMSK
• Pulse shaping
• Automatic Identification System (AIS)

Learn it step by step

• Digital modulation & constellations

From the blog

• SDR Internals, Part 6: Demodulation