Unified BER and optimum threshold analysis of binary modulations in simple and cascaded Rayleigh fading channels with switched combining

Following a unified analytical framework, the bit error rate (BER) of several coherent and non-coherent binary modulation schemes are derived for a switched diversity system. The two variants of switched combining (SWC) that have been investigated are switch and stay combining (SSC) and switch and examine combining (SEC). For channel modelling, at first a simple slow flat fading channel is assumed where the amplitude attenuation obeys the Rayleigh distribution. Later the BER calculations are repeated for cascaded Rayleigh fading channel case. Rayleigh fading is the most popular model for electromagnetic signal propagation in wireless media when both or either of the transmitter/ receiver is fixed. On the other hand, when both the transmitter and the receiver are mobile a cascaded (or double) Rayleigh fading model is better suited. The applicability of these two models, namely simple and cascaded Rayleigh model, has been indicated by several theoretical studies and their suitability is established by various field measurements. In our paper, simple closed-form BER expressions as a function of switching threshold have been found and optimum switching thresholds have been computed for both these models as well as for both types of diversity combining described earlier. The results presented in this article can be very useful for communication system designers to analyze link quality of switched diversity assisted systems in various wireless environments.