Nonlinear Filtering for Rejection ISI in FSK Modulation

We analyze the occurs error in binary FSK due to inter symbol interference (ISI) in mobile radio channels, with a limiter-filtering-integrator detector. The errors are caused by bursts in the instantaneous frequency. We propose and verify that a nonlinear frequency filtering can achieve zero error floors for pure FSK by clipping off these bursts. For filtered FSK, the error floor is not completely removed, but strongly reduced - typically by one or two orders of magnitude