Improving and Bounding Asymptotic Approximations for Diversity Combiners in Correlated Generalized Rician Fading

Although relatively simple exact error rate expressions are available for selection combining (SC) and equal gain combining (EGC) with independent fading channels, results for correlated channels are highly complex, requiring multiple levels of integration when more than two branches are considered. Asymptotic analysis has been used to derive simple error expressions valid in the high signal-to-noise ratio (SNR) region. However, it is not clear at what SNR value the asymptotic results are an accurate approximation of the exact solution. In this paper, we derive asymptotic results for SC and EGC in correlated generalized Rician fading channels. Furthermore, the asymptotic results for SC are expanded into an exact infinite series. Although this series grows quickly in complexity as more terms are included, truncation to even two or three terms has much greater accuracy than the first (asymptotic) term alone. Finally, we derive asymptotically tight lower and upper bounds on the error rate for EGC. Using these bounds, we are able to show at what SNR value the asymptotic results are valid.