Index

Low Earth Orbit Numerical Analysis & Research Tools

The FAT module proposes the simulation of a basic set of satellite-mobile radio channel fading models. In correlation with elevation data computed by the CAT module for a given constellation, the necessary fade margins can be computed for a given link availability, or, the resulting link availability computed for a given fade margin.

The FAT module proposes the simulation of a basic set of satellite-mobile radio channel fading models. Fade models that are provided are empirical and distribution models.

Empirical models are models based on measurements and provide a derived equation to compute the fade exceeded for a given link availability as a function of satellite elevation. Two models are implemented in LEONART which are the NASA ERS (Empirical Roadside Shadowing) model, and the Coverage model or Large Scale-Small Scale (LS-SS) model which are described in the NASA Reference Publication 1274. Fade or availability curves can be displayed as a function of elevation.

The distribution models provided are the Rice and Rayleigh and the Lutz fade models, which combines Rice and Rayleigh distributions in a number of environments. The Rice distribution provides a model of the unshadowed link between a satellite and a mobile, and the Rayleigh distribution a model of the shadowed link. The Lutz model takes into account the two possible states of the link (shadowed or not) to model the fade distribution in various environments from fade measurements. The FAT module enables the constitution of a Lutz model database. The density and distribution curves of each model can be displayed.

availability computations

The CAT module provides the distribution of the elevation of the best elevation satellite in visibility. The fade models provide the fade margin or either the link availability as a function of the elevation. From this two set of data, for a given constellation and users zone, and for a given fade model, the expected value of the fade margin or the link availability can be computed for each user. Fade margins and link availability reports can be edited and analyzed, for various link availability and fade margins respectively.