Gap filler technology for seamless communication on train

A further challenge consist in the selection of an appropriate technology for the GF, able to provide a sufficient robustness respect to the impairments introduced by the propagation environment.
• a transparent architecture, where the GF provides the in-tunnel coverage by just replicating the signal present on the satellite segment in a different frequency band;
• a semi-transparent architecture, where the GF just suites the signal waveform to the in-tunnel channel conditions (i.e. layers above the physical one are left unchanged);
• a non-transparent architecture, where the GF modifies not only the waveform of the signal, but also provides further functionalities (e.g. traffic filtering, QoS scheduling, etc.) up to the IP level.

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[1] Liva G, Riera Diaz N, Scalise S, et al. "Gap Filler Architectures for Seamless DVB-S2/RCS Provision in the Railway Environment," VTC Spring 2008 - IEEE Vehicular Technology Conference. 2008:2996-3000.