RFQPSK vs MSK: Modulation Techniques Compared
modulation
qpsk
msk
digital communication
rf
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This page compares QPSK (Quadrature Phase Shift Keying) and MSK (Minimum Shift Keying) modulation techniques, focusing on various system parameters.
The following table highlights the key differences between QPSK and MSK:
| Specifications | QPSK modulation | MSK modulation |
|---|---|---|
| Full form | Quadrature Phase Shift Keying | Minimum Shift Keying |
| Maximum phase change | +/-90, +/-180 degrees | +/-90 degree smoothly over the course of a bit period |
| RF Amplifier requirement | Requires a linear amplifier. Using a non-linear amplifier will result in spectral regrowth due to +/-180 phase transition. | Phase change is linear, allowing the use of a non-linear amplifier. |
| Null Bandwidth | Equal to 1.0 times the data rate | Equal to 1.5 times the data rate |
| Power | 99% power is concentrated in 1.0 (data rate) | 99% power is concentrated in 1.2 (data rate) |
| PSD (Power Spectral Density) | PSD falls off proportional to the inverse second power of frequency | PSD falls off proportional to the inverse fourth power of frequency |
| Amplitude variation | On the order of 30dB | Very less |
| Mainlobe to sidelobe suppression | Poor | Very high. Side lobes are much smaller compared to the main lobe, making filtering of the MSK modulated signal easier. |
| Width of main lobe | 1.0 times the data rate | The main lobe is wider than QPSK, i.e., 1.5 times the data rate |
| Definition | Two BPSK signals in phase quadrature | Two BPSK signals are orthogonal to one another in frequency quadrature |
