ERROR FLOOR OF MSK MODULATION IN A MOBILE-RADIO CHANNEL WITH 2 INDEPENDENTLY FADING PATHS

We investigate the error probability bit error rate (BER) of minimum s hift keying (MSK) modulation with differential detection in a two-path fading channel without noise (error floor). We develop a new method f or the computation of the BER: we show that errors occur if the phasor s of the instantaneous impulse response fall into certain regions of t he complex plane; then we average over the statistics of the phasors t o arrive at the mean BER. With this method, we derive analytical expre ssions for the BER for arbitrary amplitude statistics of the paths. Fo r the special case of two Rayleigh-fading paths with small delay, we f ind that the BER is proportional to the square of the mean delay sprea d (normalized to the bit length) if we sample between the two pulses, This proves the qualitative behavior of previous estimates, but our re sults allow also a more exact quantitative formulation. The quadratic dependence of the BER on the delay spread breaks down if we have one R ayleigh-fading and one Rician-fading path. We find that the bit combin ations 1-11 and -11-1 do not lead to errors in the two-path model. How ever, additional Monte Carlo simulations show that these bit combinati ons do lead to errors in a three-path model.