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QPSK vs MSK

This page covers comparison between QPSK and MSK modulation techniques with respect to various system parameters. Following table covers difference between QPSK and MSK.

Specifications QPSK modulation MSK modulation
Full form Quadrature Phase Shift Keying Minimum Shift Keying
Maximum phase change +/-90 , +/-180 degrees phase change of +/-90 degree smoothly over course of a bit period
RF Amplifier requirement requires linear amplifier. nonlinear amplifier if used will result into spectral regrowth due to +/-180 phase transition phase change is linear and hence allows use of nonlinear amplifier
Null Bandwidth equal to 1.0 times data rate equal to 1.5 times 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 inverse second power of frequency PSD falls off proportional to inverse fourth power of frequency
Amplitude variation on the order of 30dB very less
mainlobe to sidelobe suppression poor is very high. Side lobes are much smaller compare to main lobe and hence filtering of MSK modulated signal is easier.
width of main lobe 1.0 times data rate main lobe is wider than QPSK i.e. 1.5 times data rate
definition two BPSK in phase quadrature two BPSK signals are orthogonal to one another in frequency quadrature

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