Gaussian Minimum shift Keying-GMSK

Описание: The Gaussian Minimum Shift Keying (GMSK) is a binary modulation technique that is derived from Minimum Shift Keying (MSK) Technique.
By applying a Gaussian low pass filter with MSK, a GMSK signal can be derived.
That is passing the modulating non return to zero (NRZ) waveform through the pre-modulation pulse shaping filter which is Gaussian.
The output is obtained with reduced sidelobes in the transmitted spectrum.
The GMSK signal can be coherently or non-coherently detected like FSK.

Baseband Gaussian pulse shaping smooths the pulse trajectory of the MSK signal and hence stabilizes the instantaneous frequency variations over time.
This has the effect of considerably reducing the sidelobe levels in the transmitted spectrum.

Pre-modulation Gaussian filtering converts the full response message signal ( where each baseband signal occupies a single bit period T) into a partial response scheme where each transmitted symbol spans several trajectory to deviate from the simple MSK.
However, since pulse shaping does not cause the pattern-averaged phase trajectory to deviate from that of simple MSK.
GMSK can be coherently detected just as an MSK signal, or non-coherently detected as simple FSK.
In practice, GMSK is most attractive for its excellent power efficiency (due to constant envelope) and its excellent spectral efficiency.