W. Chung, C.R. Johnson, Jr., and M.J. Ready
IEEE Signal Processing Letters, January 2002, pp. 26--28.
We characterize the nonlinear distortion of frequency-shift keying (FSK) signals due to a multipath channel as a linear time varying channel. The dynamic range of time variation of this time-varying channel model is small for a mild multipath channel and large for a severe multipath channel. This characterization justifies the use of a decision directed adaptive linear equalizer for FSK signals after frequency demodulation in order to mitigate the distortion due to a multipath channel.