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Communications Blockset 4.3
Filtered QPSK vs. MSK
This demo enables you to visually compare filtered quadrature phase shift keying (QPSK) and minimum shift keying (MSK) modulation schemes.
Contents
Structure of the Demo
This demo uses various Communications and Signal Processing Blockset™ blocks to model filtered QPSK and MSK modulation.
The demo includes these blocks:
- Sources of uniformly distributed random integers between 0 and M-1, where M is the constellation size of the modulation scheme. Two sources are required, because QPSK is a quaternary modulation method, while MSK is a binary modulation method.
- The QPSK Modulator Baseband block
- The MSK Modulator Baseband block
- The Raised Cosine Transmit Filter block
- The AWGN Channel block
- The Discrete-Time Eye Diagram Scope block
Results and Displays
The demo includes these visual aids to illustrate the difference between the two modulation schemes:
Eye diagram blocks that show the eye diagrams of filtered QPSK and MSK signals plus noise:
1. In filtered QPSK, the values of both the in-phase and quadrature components of the signal are permitted to change at any symbol interval.
2. However, for MSK, the symbol interval is half that for QPSK, but the in-phase and quadrature components change values in alternate symbol epochs. Therefore, the ideal sampling time for QPSK is 0.5, 1.5, 2.5,..., while the ideal sampling period for MSK is 0.5, 1.5, 2.5,... for the in-phase signal and 1, 2, 3,... for the quadrature signal.
