Existing Studies, Projects and Solutions
Studies and Projects
Several studies and projects have been performed from satellite technologies. A survey on mobile satellite systems is presented in . The report details the existing standards (such as S-UMTS, DVB-S2, DVB-SH) and the existing mobile satellite systems (such as Inmarsat, Globalstar, Thuraya). The different systems are then compared based on a number of criteria (frequency bands, PHY layer characteristics, multiple access techniques, satellite characteristics). A tutorial on satellite systems for Internet access is presented in . More details of these two reports are given in Appendix B.4.
As presented above, when the satellite link is blocked, the TAT switch to a terrestrial network. This solution of “gap-filler” was first introduced in the ROSIN (Railway Open System Interconnection Network) project in 1999 , which intended to develop a system allowing supervising equipments on board trains thanks to a GSM connection between the train and the control center. The ROSIN project aimed to validate a complete and open platform, which represented the basis for a new generation of vehicles, consisting of an on board network that interconnects all various on board systems and subsystems. Works were pursued with the TRAINCOM  and the FIFTH  projects.
TRAINCOM  is a European project finished in 2003. 13 partners worked on the project, such as Siemens, Bombardier, Alstom, DB, and Trenitalia. During project life, two important railway operators, SNCF (France) and SBB (Switzerland), joined the TRAINCOM project as Observer Participants. The project aimed to develop a reliable communication system between the train and the ground, offering access to on board equipments and integration of all new available technologies (GSM or GSM-R links, protocols and language of Internet such as TCP/IP). The train was then connected to the ground with several wireless connections, and it could switch between them according to required bandwidth for a given application.
FIFTH (Fast Internet for Fast Train Hosts) project proposed a new network solution able to provide a broadband Internet access to passengers on board HST via satellite solutions. A new satellite technology was studied and a prototype was designed and developed in order to implement a practical demonstrator. The prototype was based on two subsystems: the railway mobile terminal and the network access infrastructure. The railway terminal was composed of the satellite network access interface and all the subnetworks in the train for passengers (servers and users terminals). Tracking and pointing techniques were based on a GPS navigation system and an inertial technique (gyroscope). A bidirectional satellite solution used in “classical trains” (non high speed) provided a communication with throughputs of about 2 Mbps/512 kbps (download and upload respectively).
The solution was then integrated under the INTEGRAIL project [30, 31], in the context of an intelligent integration of railway information system. Other works evaluate the TCP flows of satellite systems . Finally, the TRAINIPSAT project  aimed to define, specify and test a technical solution to provide connectivity services for HST, both for individuals and professionals. The objective of the project was to demonstrate the feasibility and relevance of a solution combining a bidirectional satellite link and a terrestrial link, and a seamless connectivity on board train via a network such as Wi-Fi. The terrestrial link, based on the WiMAX technology, was specifically designed to take into account technical constraints due to fast mobility. The satellite link was explored with the development of a predictive model of availability of satellites, relying on Markov models. Mobility management and handover mechanisms were also investigated.
Some experiments were performed in Spain in the AVE trains (High Speed Trains) of the RENFE with Indra. Indra  is a multinational located in Spain and Latin America. It provides solutions and services in different domains, such as transportation, traffic, energy or industry. Indra experimented a solution to provide broadband Internet access on board trains. The system is based on a bidirectional satellite connection using Demand Assigned Multiple Access (DAMA) access scheme in order to optimize the use of the frequency band. Frequency bands are then automatically assigned to mobile terminals, depending on their needs. Indra’s system manages three satellite technologies: DVB-S for downlink, wide spectrum Code Division Multiple Access (CDMA) for uplink, and Single Channel Per Carrier (SCPC) for both links, coexisting with SCPC and/or CDMA. Test measurements were performed on the line between Barcelona and Madrid. No further information could be found on these trials.