Terminology » Modulation » QPSK vs MSK: Modulation Techniques Compared

QPSK vs MSK: Modulation Techniques Compared

modulation qpsk msk digital communication rf

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:

SpecificationsQPSK modulationMSK modulation
Full formQuadrature Phase Shift KeyingMinimum Shift Keying
Maximum phase change+/-90, +/-180 degrees+/-90 degree smoothly over the course of a bit period
RF Amplifier requirementRequires 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 BandwidthEqual to 1.0 times the data rateEqual to 1.5 times the data rate
Power99% 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 frequencyPSD falls off proportional to the inverse fourth power of frequency
Amplitude variationOn the order of 30dBVery less
Mainlobe to sidelobe suppressionPoorVery high. Side lobes are much smaller compared to the main lobe, making filtering of the MSK modulated signal easier.
Width of main lobe1.0 times the data rateThe main lobe is wider than QPSK, i.e., 1.5 times the data rate
DefinitionTwo BPSK signals in phase quadratureTwo BPSK signals are orthogonal to one another in frequency quadrature