Report of GMSK Modulation
Theory of GMSK modulation:
GMSK——Gaussian minimum shift keying, signal of GMSK is produced by going through the Gaussian low-pass filter before passing the CPM modulator(h=0.5).
Schematic of GMSK modulation:
g(t) is rectangular impulse response of the Gaussian filter.
When BT=Bb*Tb=0.2, 0.3 and 0.5, the rectangular impulse responses of the Gaussian filter in one symbol period are as follows.
Simulation in Matlab；
Here, we set that input data is s=[1 1 1 0 0 0 1 1 0 1], symbol period is Tb=0.1s, Gaussian filter’s 3dB bandwidth is Bb=3; modulation index is h=0.5, sampling frequency is fs=2kHz, carrier frequency is fc=20Hz.
As with g(t), we choose the situation of BT=0.3, then we implement the simulation of GMSK modulation as the schematic in Matlab.
Here is the code:
s=[1 1 1 0 0 0 1 1 0 1]; n=length(s);
plot(t,g);title('BT=0.3 g(t) in one symbol period');
title('Phase route of GMSK'); subplot(2,1,2);plot(t,gmsk);grid on;
Results of simulation:
After the simulation, we get the results of GMSK signal phase route
and the GMSK waveform.