Analysis Influence of NFD Filter in FSK Modulation for Reduction ISI

We analyze the error floor of binary FSK due to inter symbol interference in time-dispersive mobile radio channels, with a limiter-discriminator-integrator detector. The errors are caused by bursts in the instantaneous frequency. We propose and verify that a nonlinear frequency discriminator can achieve zero error floor 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. The NFD can be also used in conjunction with adaptive sampling