A Systemic Approach to the Compensation of Rain Attenuation in Ka-Band Communication Satellites

Rain attenuation at Ka-band is a severe phenomenon that drastically impairs satellite communications at these frequencies. Several adaptive compensation techniques have been elaborated to counteract its effects and most often applied one at a time. The present paper proposes the contemporary exploitation of different techniques in a combined approach. Such an integrated approach is thoroughly analyzed in a simplified scenario and will be shown to achieve a very effective solution, making the Ka-band spectrum fully available for broadband satellite applications and network-centric systems. 1. Introduction The advent of Ka-band (The frequency bands 17.7–21.2？GHz (space to Earth) and 27.5–31？GHz (Earth to space) have been allocated by the International Telecommunication Union (ITU) for the use of Fixed Satellite Services (FSS)) satellite communications is driven by the diffusion of consumer applications (such as High Definition Television broadcasting) and by the increased demand for broadband networks in network-centric systems. The network-centric architecture, originally conceived for military applications, is becoming a paradigm for large integrated systems, or “systems of systems”, able to collect and to convey data seamlessly throughout a number of different possible media and to deliver useful information after a data fusion process. Ka-band space segment and ground segment technologies, after a pioneering phase (Italsat [1, 2], ACTS [3]) and a successive consolidation, are now mature for cost-effective and reliable commercial missions. One the major drawbacks still affecting Ka-band satellite communications is that related to rain attenuation. Rain attenuation in satellite communication systems operating at Ka-band frequencies is much more severe than that usually experienced at lower frequency bands: rain attenuation at 20？GHz (Ka-band down-link), for instance, is almost three times that at 11？GHz (Ku-band down-link) [4, page 125]. This fact makes rain attenuation one of the most important limiting factors to be taken into account in the design of a 20/30？GHz satellite communication system. A number of mitigation techniques has been envisioned and experimented over the years, in the attempt to overcome the problem and to make Ka-band satellite applications as commercially viable as those at Ku band [5, Chapter 8]. One first classification of such techniques is between ground-based and space-based solutions. Ground-based techniques are those basically operated on ground (either in open- or closed-loop configurations) and only indirectly affecting