This model shows Gaussian minimum shift keying (GMSK) and minimum shift keying (MSK) modulation schemes and visually compare them.
The example model includes these blocks:
The Random Integer block, which provides a source of uniformly distributed random integers in the range [0, M-1], where M is the constellation size of the GMSK or MSK signal
The Unipolar to Bipolar Converter block
The GMSK Modulator Baseband block
The MSK Modulator Baseband block
The AWGN Channel block
Two copies of the Discrete-Time Eye Diagram Scope block
Two copies of the Discrete-Time Signal Trajectory Scope block
The example illustrates the difference between the two modulation schemes. The Discrete-Time Eye Diagram Scope blocks show the eye diagrams of GMSK and MSK signals corrupted by noise.
The eye diagrams show the similarity between the GMSK and MSK signals when you set the Pulse length of the GMSK Modulator Baseband block to 1. Setting the Pulse length to 3 or 5 enables you to view the difference that a partial response modulation can have on the eye diagram. The number of paths increases, showing that the CPM waveform depends on values of the previous symbols as well as the present symbol. You can change the pulse length to 2 or 4, but you should change the Phase offset to pi/4 for a better view of the modulated signal. In order to more clearly view the Gaussian pulse shape, you must use scopes that enable you to view the phase of the signal, as described in CPM Phase Tree Example.