  This work is devoted to the formulation and derivation of the
$\kappa-\mu$/gamma distribution which corresponds to A physical fading model.
This distribution is composite and is based on the well known $\kappa-\mu$
generalized multipath model and the gamma shadowing model. A special case of
the derived model constitutes the $\kappa-\mu$ Extreme/gamma model which
accounts for severe multipath and shadowing effects. These models provide
accurate characterisation of the simultaneous occurrence of multipath fading
and shadowing effects. This is achieved thanks to the remarkable flexibility of
their named parameters which render them capable of providing good fittings to
experimental data associated with realistic communication scenarios. This is
additionally justified by the fact that they include as special cases the
widely known composite fading models such as Rice/gamma, Nakagami-m/gamma and
Rayleigh/gamma. Novel analytic expressions are derived for the envelope and
power probability density function of these distributions which are expressed
in a relatively simple algebraic form which is convenient to handle both
analytically and numerically. As a result, they can be meaningfully utilized in
the derivation of numerous vital measures in investigations related to the
analytic performance evaluation of digital communications over composite
multipath/shadowing fading channels.
