Link Performance for a Satellite-Based Communications System for Fast Trains: Analysis of Trials and Measurements

The railway environment constitutes an extremely challenging scenario for satellite based communications: in additional to the usual impairments characterising the land mobile satellite channel, such as shadowing and blockage effects due to obstacles like trees, building or bridges, one has to consider the presence of additional elements such as catenaries, electrical posts and trellises, typical of all electrified railway lines, the frequent occurrence of tunnels, whose length may easily reach several kilometres and the existence of large train stations, where the satellite is normally not visible. For the latter two cases (long tunnels and train stations), proper gap fillers such as terrestrial repeaters have to be envisaged. On the other hand, for mainly open areas, a variety of countermeasures at both physical and network layer has been studied to overcome the above described channel impairments and guarantee a resulting link availability permitting to support broadband internet connections and multimedia services, e.g. dedicated digital TV.