Analysis of Post-Demodulator Adaptive Filter Behavior to Compensate for Multipath Channels for FSK Signals

Analysis of adaptive filters positioned after FSK demodulators and the statistics of their non-Gaussian noise environment are used to extend previous analytical and simulation studies. Equalization of multipath channels for FSK signals is typically accomplished with an adaptive filter at the receiver before demodulation. Motivated by a desire to reduce computation, a post-demodulator adaptive filter was proposed, and simulations using multipath models derived from physical channel measurements showed promise. However, previous systematic simulation and theoretical analysis of short multipath channels have led to ambiguous results. This paper analyzes the non-Gaussian statistics of the filter input and, for longer multipath channels, shows why increasing the filter length does not improve performance and why the converged LMS filter produces a BER higher than the minimum achievable by a linear filter.