Atmospheric scintillation causes fading to a free-space optical communications link. Optical communication links can be improved by the correct application of coding schemes customized to meet the atmospheric conditions. For this paper, we model atmospheric scintillation using a gamma-gamma probability distribution. From the scintillation model, the equations are derived for probability of fade along with mean fade time and the duration of fade. Parameters for the gamma-gamma model, directly related to atmospheric conditions, are used to compute theoretical cases of fading in weak and strong atmospheric turbulence. With the models for atmospheric fading, different coding techniques on a pulse-position modulation optical link are examined.© (2004) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.