Unified analysis of switched diversity systems in independent and correlated fading channels

The moment generating function (MGF) of the signal power at the output of d ual-branch switch-and-stay selection diversity (SSD) combiners is derived. The first-order derivative of the MGF with respect to the switching thresho ld is also derived. These expressions are obtained for the general case of correlated fading and nonidentical diversity branches, and hold for any com mon fading distributions (e.g., Rayleigh, Nakagami-m, Rician, Nakagami-q). The MGF yields the performance (bit or symbol error probability) of a broad class of coherent, differentially coherent and noncoherent digital modulat ion formats with SSD reception. The optimum switching threshold (in a minim um error rate sense) is obtained by solving a nonlinear equation which is f ormed by using the first-order derivative of the MGF. This nonlinear equati on can be simplified for several special cases. For independent and identic ally distributed diversity branches, the optimal switching threshold in clo sed form is derived for three generic forms of the conditional error probab ility. For correlated Rayleigh or Nakagami-m fading with identical branches , the optimal switching threshold in closed form is derived for the noncohe rent binary modulation formats. We show Previously published results as spe cial cases of our unified expression. Selected numerical examples are prese nted and discussed.