Approximate capacity analysis for distributed MIMO system over Generalized-K fading channels

In this paper, we provide a Gamma distribution to approximate composite Gamma-Gamma (Generalized-K or K_G) distribution by using the moment matching method. Based on the approximate distribution, we propose a novel closed-form approximate upper bound of D-MIMO system. The proposed upper bound, which enable us to go further manipulations, only involves some simple functions. Starting from the approximate upper bound, we perform a high-SNR analysis and investigate the asymptotic behavior of the capacity in the following two cases: i) the number of receive antennas grows into infinity for the fixed average and total transmit power, and ii) the number of antennas at both ends grow large at a fixed ratio. It is demonstrated that the proposed approximate and the asymptotic upper bounds match accurately with the exact analytical expression.