Integrated Public Mobile Radio Networks/Satellite for Future Railway Communications
The European train control system employs GSM-R for communications between trains and the command/control centers. GSM-R technology is quite old and will be replaced in the near future by other technologies offering less expensive solutions, especially for regional and local lines. This article investigates a new telecommunication solution based on multi radio bearers using cellular and satellite public networks as an alternative to the deployment of a dedicated infrastructure. A test campaign on a 300 km of rail line (about 10,000 km of tests) has been carried out to evaluate the performance of cellular and satellite networks in a railway environment. Test trial results presented and discussed in this article have been used to assess the performance of a multipath TCP protocol to effectively support multi-bearer communications. A discussion of the economic benefits and the potential industrial implications of the proposed solution concludes the article.
Challenges arise: to comply with the interoperability requirement and, from the train operator side, to protect their investment in GSM-R. Already, a migration path to a fully IP-based system has started, and 4G and the incoming 5G could facilitate the evolution toward a full service-based system for every rail application . Concerning cost reduction, a first significant breakthrough in economic sustainability is represented by the replacement of proprietary, dedicated networks with commercial public land mobile networks (PLMNs) and satellite. The use of public telecommunication infrastructure(s) makes it possible to rapidly extend the existing automated train control procedures (such as the European Rail Traffic Management System/European Train Control System (ERTMS/ETCS), and communications based train control ) for improving rail traffic capacity for local/regional lines where the deployment of a dedicated radio infrastructure is expensive in terms of both CAPEX and OPEX. Furthermore, public networks can be considered as low cost and effective enablers for the rapid deployment of the modern railway information systems such as that proposed and investigated in the InteGRail project, .
In this article we evaluate the performance of train control systems adopting PLMNs for signaling. The considered system jointly uses all the available best-effort bearers, which are intelligently managed by an on-board multipath router device, i.e., the multiple access router (MAR). The MAR adopts the multipath TCP (MPTCP) protocol . To further improve performance, we propose the integration of a guaranteed QoS link provided by satellite in case of unavailable or congested PLMNs. Experimental data concerning the endto- end delay and link availability are presented and discussed in this article for both terrestrial and satellite links. These data have been used to evaluate the overall end-to-end delay for the (typical) message exchange procedure between the train and the control center based on the MPTCP protocol. Results can be used by the railway operator to infer the achievable QoS for the typical train control procedures.
This article proposes a new solution based on cellular and satellite public networks to reduce the costs of a dedicated telecommunication infrastructure in accordance with the objectives of the future evolution of the ERTMS train control system. The novelty consists in a multi-bearer communication solution based on the MPTCP, making use of an integrated PLMN/satellite network with an on-board intelligent routing mechanism to provide the required QoS. This solution is particularly attractive for regional and local traffic lines, most of which require huge investments to be upgraded. Our solution may contribute to the adoption of a cost efficient ERTMS system to replace the existing and obsolete equipment. To assess the validity of the PLMN/satellite solution, we used experimental results obtained from a comprehensive test trial in Sardinia, Italy, to evaluate the MPTCP’s performance. Results in terms of achievable link reliability and E2E delays are encouraging for the adoption of a PLMN/ satellite approach to export ERTMS/ETCS procedures.
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 “Satellite Communication to Support EU Security Policies and Infrastructures Concept,” available at http://www.pwc. fr/assets/files/pdf/2015/02/pwc_concept_paper_satcom. pdf.
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 Next Generation Train Control 7th FP program, http:// cordis.europa.eu/project/rcn/110543_it.html
 R. Alvarez and J. Roman, “ETCS L2 and CBTC over LTE — Convergence of the Radio Layer in Advanced Train Control Systems,” The Institution of Railway Signal Engineers (IRSE) Australasia Technical Meeting, Perth, Australia, 18 Oct. 2013.
 InteGRail — Intelligent Integration of Railway Systems, Project no. FP6 — 012526, website: www.integrail.info and www.integrail.eu.
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