EHF Propagation Experiment with Syracuse 3 Satellite: First Results

An Earth-to-satellite propagation experiment operating at EHF band was set up within the framework of the Syracuse 3 program. Syracuse 3 satellites are the new generation of French military SATCOM system. This experiment is a good opportunity to make attenuation measurements and increase our knowledge of tropospheric propagation effects on EHF links at a low elevation angle (17deg). At these frequencies (20 & 44 GHz), the attenuation due to the troposphere can be very strong. Although rain is the major contributor, clouds and gases are no longer negligible, and contribute in a significant way to attenuation, especially above 40 GHz. Among the various fade mitigation techniques, we will focus in a second part on an Up-Link Power Control technique. This technique consists in a real-time uplink adjustment of transmitted power according to the channel attenuation conditions. The channel propagation conditions are generally estimated at a lower frequency, using the downlink (20 GHz). Due to the delay of the control loop, the power margin has to be estimated a few seconds in advance, typically 10 seconds. A new prediction method based on an ARMA/GARCH model is proposed. This non-linear model originally proposed for financial studies is shown to be accurate to describe the attenuation process, which exhibits volatility clusters (periods with sudden and strong variations). Comparisons with other existing models are presented.