Unified Probability Distributions of Composite Fading for Radio Frequency and Optical Wireless Channels

We derive novel unified probability density function (PDF) formulae of the instantaneous envelope, power and signal-to-noise ratio (SNR), for a generalized composite fading process that models the multiplicative effect of small-scale fading and large-scale shadowing/fluctuations in radio frequency and free-space optical wireless communications channels. By specifying four fading parameters according to specific composite fading models, the unified PDF formulae enable us to unify and characterize wide ranging of existing and numerous novel generalized composite fading distributions. We also present unified analysis and derive general closed form formulae for channel capacity in terms of four parameters of the unified PDF. Such generalized performance metrics can then be further specified and evaluated according to various known and numerous novel composite fading channel models.