  In this paper, we introduce a generalized composite fading distribution
(termed extended generalized-K (EGK)) to model the envelope and the power of
the received signal in millimeter wave (60 GHz or above) and free-space optical
channels. We obtain the first and the second-order statistics of the received
signal envelope characterized by the EGK composite fading distribution. In
particular, expressions for probability density function, cumulative
distribution function, level crossing rate and average fade duration, and
fractional moments are derived. In addition performance measures such as amount
of fading, average bit error probability, outage probability, average capacity,
and outage capacity are offered in closed-form. Selected numerical and computer
simulation examples validate the accuracy of the presented mathematical
analysis.
