A unified low elevation angle scintillation model

Enabling communications at very low elevation can lengthen the pass duration between a satellite and a ground station, which in turn can increase the amount of data return and possibly reduce the number of required supporting ground stations. Link performance, especially at very low angles and high frequencies, depends heavily on terrain, atmosphere, and weather, etc. Among the different crucial attenuations, scintillation fading plays a significant role and can greatly impair the performance of the link. It is therefore necessary to model correctly the overall impacts to the link due to scintillation fading. The current International Telecommunication Union Recommendation ITU-R P.618-10 describes three scintillation loss models depending on the elevation angles and percentage of time for which the loss exceeds certain threshold. Implementation of the recommendation resulted in many issues. Particularly, it was identified that (i) iterative solutions to an implicit nonlinear exponential model cannot be found in some cases, (ii) there is a discontinuity in fading values, (iii) scintillations at lower elevation angles from a model are unrealistically lower, (iv) for elevation angle between four and five degrees, there are two applicable scintillation models which yield conflicting values. In this article, we develop a new approach to unify the different fading models within the current ITU recommendation and remove the discrepancies completely. We further validated our models using the ITU-adopted scintillation data measured at Goonhilly, Great Britain and several recent NASA´s Space Shuttle launches. This improved model has been provisionally approved in the ITU International Meeting in Italy, November 2010, and is being evaluated by the ITU members for adoption into the next version ITU Recommendation ITU-R P.618-10.