Comparing Models and Approximations of Beam Wander

Free space optical communication is a new and promising area with many desirable properties. However, there is no standardized way to model losses and effects of the atmosphere on the propagating beam. This necessitates comparing different models and approximations that are widely used in the literature. We calculate and compare various aspects of beam wander under realistic scenarios. We compare two formulas for the one axis RMS tilt and conclude that they give approximately the same answer under a wide range of scenarios including various optical turbulence models. We also examine the effects of neglecting the Earth's curvature which is an approximation in multiple influential papers. We modify existing equations in the literature to assume a perfectly round Earth. We also examine the beam wander in case of adaptive optics. We conclude that neglecting the curvature introduces no meaningful error when the beam wander is expressed as an angle but can significantly affect the beam wander induced beam displacement expressed in meters. The error is more prominent for GEO satellites and can be meaningful even at small zenith angles.