Filtered QPSK vs. MSK

This model shows filtered quadrature phase shift keying (QPSK) and minimum shift keying (MSK) modulation schemes and visually compare them.

Structure of the Example

This example, doc_qpsk_vs_msk, uses Communications Toolbox™ blocks to model filtered QPSK and MSK modulation.

The example model includes these blocks:

Results and Displays

The example uses eye diagram blocks to show the eye diagrams of filtered QPSK and MSK signals plus noise. You can observe that:

  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.