Multipath effects of FSK with frequency-discriminator detection

We analyze how multipath effects, namely, errors due to channel-induced intersymbol interference, influence the error probability of frequency shift keying (FSK) with frequency-discriminator detection. We first introduce a new mathematical technique that allows insights into the error mechanisms. This technique is also capable of dealing with frequency shifts of the multipath components, postdiscriminator filtering, and nonlinearities in the discriminator. We then show that increasing the modulation index decreases the error floor, especially in the presence of frequency shifts. We also discuss the differences between prediscriminator and postdiscriminator filtering and show that an integrator is the best postdiscriminator filter.