Frequency Shift-Keying (FSK) Error
For an M-ary FSK system, the average FSK error is defined as the average root mean squared (RMS) spread of the FSK demodulated symbol spaced waveform around the ideal symbol (frequency) locations.
Mathematically, the FSK error is defined as
where
M is the FSK modulation format
ƒideal,i is the ideal symbol location at the FSK frequency corresponding to location i
ƒactual,i represents the value of the demodulated symbols at location i
In the preceding figure, the points represent the actual FSK demodulated symbol locations, and the vertical lines represent the ideal symbol locations for a 4-FSK format.