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This model shows Gaussian minimum shift keying (GMSK) and minimum shift keying (MSK) modulation schemes and visually compare them.

Structure of the Example

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

Results and Displays

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.

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