Statistical Analysis of Fading Power Vectors for Real-Time Atmospheric Channel Emulation

The design and testing of a free-space optical communication system requires assessment of the impact of
random fluctuations in received power from a laser beam transmitted over an atmospheric channel. A number
of methods for generating fading power vectors for in-lab emulation of an atmospheric channel have previously
been reported. These techniques include spectral shaping and filtering of a signal from a normally distributed
pseudo-random number generator, full wave optics simulations with random phase screens, and pre-recorded
measurements from experimental free-space links. In this work, a statistical analysis of atmospheric fading is
presented with the goal of producing a practical engineering model for the fading channel suitable for generating
synthetic fade vectors in real-time for long-duration receiver testing with channel interleaving. Specifically, a
parametric model is developed for turbulence-induced fade on space-to-ground links with large-aperture receivers,
including aperture-averaging and the effects of aperture size on the instantaneous coupling efficiency for mode-
limited receivers. In particular, we analyze the probability density function and temporal power spectrum for
fluctuations of the coupling efficiency for few-mode fibers in a range of turbulence conditions.