On the Approximation of the PDF of the Sum of Independent Generalized-K RVs by Another Generalized-K PDF with Applications to Distributed Antenna Systems

The generalized-K (Gamma-Gamma) composite fading model has been proposed in the past to represent the statistics of the instantaneous power of target and clutter scattering in radar systems. Recently, this model was used in wireless communications as an alternative to the analytically intractable lognormal-based composite fading models. In this paper, a simple approach is proposed to approximate the probability density function of the sum of independent generalized-K random variables by another generalized-K one using the moment matching method. The numerical evaluations show that the proposed approximation of the sum distribution is sufficiently accurate for realistic scenarios in wireless channels. Furthermore, the applications of the obtained closed-form expressions to the performance analysis of distributed antenna systems are presented.