On the Statistics of the Sum of Correlated Generalized-K RVs

Appropriate channel modeling plays an important role in the design and analysis of various transmission and reception schemes over composite fading channels. The generalized-K (Gamma-Gamma) composite fading model has been used recently to model composite fading in wireless channels as an alternative to the less tractable lognormal-based models. In this paper, the expression of the amount of fading for the sum of correlated generalized-K random variables is derived and then the moment matching method is used to approximate, in the lower tail region, the probability density function of the sum of identically distributed generalized-K random variables with positively and equally correlated shadowing components by the familiar Gamma distribution. Furthermore, the obtained expressions of the amount of fading give insights into the effect of shadowing correlations on the performance of maximal ratio combining receivers in coordinated multi-point transmission and reception schemes in future wireless systems.