https://nl.mathworks.com/help/comm/ref/comm.fskdemodulator-system-object.html
comm.FSKDemodulator - Demodulate using M-ary FSK method - MATLAB
The comm.FSKDemodulator System object noncoherently demodulates a signal that was modulated using the M-ary frequency shift keying (M-FSK) method.
commusingaryfskmethod