On the utility of gamma PDF in modeling shadow fading (slow fading)

Shadow fading causes random fluctuations of the envelope mean at the mobile. The lognormal distribution is widely accepted for this phenomenon. In this paper we argue that, based on theoretical results and measured data, gamma distribution does the job as well. Then we show that by using the gamma distribution and in contrast with the use of the lognormal distribution, we can obtain easy-to-use and closed-form composite PDFs for fading channels, which in turn extremely simplify analytic calculations