Communications Blockset

GMSK vs. MSK Demo

The GMSK vs. MSK demo, gmskvsmsk, visually compares Gaussian minimum shift keying (GMSK) and minimum shift keying (MSK) modulation schemes. This document highlights these aspects of the demo:

• Structure of the Demo
• Visible Results of the Demo

Structure of the Demo

This demo uses various Communications and DSP Blockset blocks to model GMSK and MSK modulation schemes. The demo includes the following blocks:

• 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
• Unipolar to Bipolar Converter block
• GMSK Modulator Baseband block
• MSK Modulator Baseband block
• AWGN Channel block
• Two copies of the Discrete-Time Eye Diagram Scope block
• Two copies of the Discrete-Time Signal Trajectory Scope block

Visible Results of the Demo

The demo illustrate 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 demonstrating 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 instrumentation that enables you to view the phase of the signal, as in described in CPM Phase Tree Demo.

CPM Phase Tree Demo

Filtered QPSK vs. MSK Demo