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Dieses Kapitel befasst sich mit der entscheidenden Rolle von FRMCS (Future Railway Mobile Communication System) als Nachfolger von GSM-R und unterstreicht die Notwendigkeit, die Eisenbahnkommunikation zu modernisieren und intelligente Zugtechnologie zu ermöglichen. Der Text untersucht die Architektur von FRMCS, einschließlich der Einführung von FRMCS-Gateways, die Eisenbahnanwendungen vom Telekommunikationsnetz entkoppeln und eine nahtlose Weiterentwicklung zu neuen Funktechnologien ermöglichen. Außerdem wird die Integration von Eisenbahnanwendungen durch standardisierte Schnittstellen und der Einsatz von 3GPP Mission Critical Services (MCX) zur Sicherstellung relevanter Funktionalitäten und Leistungsanforderungen diskutiert. Das Kapitel gibt einen Überblick über den Status der FRMCS-Einführung, einschließlich des Plans der UIC und der Erfolge des 5GRAIL-Projekts, das die FRMCS-V1-Spezifikationen durch Labor- und Feldtests validierte. Darüber hinaus werden die zukünftigen Schritte für FRMCS V2 und den europäischen MORANE-2-Test abgedeckt, der sich auf Feldtests mit konventionellen und Hochgeschwindigkeitsstrecken unter grenzüberschreitenden Bedingungen konzentrieren wird. Der Text behandelt auch wichtige Errungenschaften des 5GRAIL-Projekts, wie die Einführung von Railway Emergency Communication (REC) und die Zusammenarbeit von FRMCS und GSM-R. Abschließend wird auf die Bedeutung der grenzüberschreitenden Umsetzung für den nahtlosen Zugverkehr zwischen den Ländern und die laufenden Arbeiten zur Fertigstellung der FRMCS V2-Spezifikationen eingegangen.
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Abstract
Future Railway Mobile Communication System (FRMCS) will be the 5G SA MCX standard for railway operational communications, conforming to European regulation. It will also fulfil the needs of rail organisations worldwide. UIC (International Union of Railways) is leading the design, standardisation, and is deeply involved for the introduction plan of this telecommunication system, in close cooperation with railways, authorities and suppliers. FRMCS is the successor of GSM-R which is a component of European Railway Traffic Management System (ERTMS), representing around ~130,000 km of coverage of tracks in Europe. GSM-R is however announced to become obsolete soon due to its 2G technology. Therefore, FRMCS, being specified and implemented as a standard, combining 5G transport with Mission Critical (MC) service layer features, is considered as a major trigger for the wide-ranging digitalization of the rail sector, satisfying the increasing demand of data while keeping the high quality of service for critical railways applications, in an interoperability context.
This paper aims to present some insights of the FRMCS introduction plan and provide an overview of the outcomes of 5GRAIL, an EU Horizon 2020 project coordinated by UIC, as part of the FRMCS readiness initiative.
The introduction of FRMCS (Future Railway Mobile Communication System), the GSM-R successor, is mandatory need not only due to the obsolescence of the 2G technology on which GSM-R is based, but also to enable the smart train, via the 3GPP 5G and MCX features. Obviously, the need for this new technology is a prerequisite for the evolution of ERTMS (European Railway Traffic Management System) whilst also being a trigger for the wide-ranging digitalization of the rail sector.
FRMCS relies on the 3GPP (3rd Generation Partnership Project) technology, 5G Core and Access networks, supporting at minimum the Railway Mobile Radio (RMR) harmonized spectrum for Europe (as per Electronic Communications Committee (ECC) (20)02 decision), and ensuring the relevant functionalities and performance requirements per railway application obtained through the 3GPP Mission Critical Services (MCX).
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One key element of this new architecture is the introduction of the so-called FRMCS gateways in the end-to-end communication chain, providing the decoupling between railway applications and telecommunication network, which allows the transport layer to evolve e.g., to a new radio technology without impacting the application layer. Connections between the on-board and the trackside parts of each application go through the two FRMCS gateways, located on both sides of the 5G infrastructure, as described below:
The On Board FRMCS gateway (OB_GTW), also known as TOBA (Telecom On-board Architecture) is connected to the applications through OBapp interface and to the 5G Radio Access Network, through a set of FRMCS modems.
The Trackside FRMCS gateway (TS_GTW) is connected to the applications through TSapp interface and to the 5G Core Network.
The usage of these standardized interfaces allows any newly created application to be easily inserted in the FRMCS system.
The below figure presents, as an example, the 5GRAIL1 project applications integration via On-Board and Trackside FRMCS Gateways (Fig. 1):
Fig. 1.
Integration of 5GRAIL applications via FRMCS Gateways [3]
Reproduced with permission from Kontron Transportation, copyright Kontron Transportation, 5GRAIL Project 2020–2023.
Moreover, the implementation of FRMCS services is based on one MCX server, located in the infrastructure, and MCX clients, on each side of the FRMCS infrastructure. Railway applications shall use the appropriate client to interconnect both parts of an application, this being one of the key principles of the FRMCS System architecture. There are two integration options for the MCX clients:
the MCX client is embedded in the application; defined as tight coupling mode.
or the MCX client is embedded in the gateways, defined as loose coupling mode.
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2 Status of FRMCS Introduction
UIC has elaborated a complete plan to introduce FRMCS [1]:
Thanks to the UIC 3GPP task force, some solutions were standardized starting from R17 and continue in R18 and beyond. Moreover, missing requirements were added to the 3GPP R19 specifications, based on the continuous gap analysis between them and he UIC FRMCS FRS (Functional Requirement Specifications).
UIC has published well in advance the FRMCS architecture principles and the migration scenarios for ETCS and voice.
The RMR spectrum was allocated to FRMCS in Europe with the ECC (20) 02 decision.
5G FRMCS chipsets in bands n100 (FDD (Frequency-Division Duplexing), Uplink (UL): 874.4-880MHz, Downlink (DL):919.4-925MHz) and n101 (TDD (Time-Division Duplexing), 1900–1910 MHz) have been provided as prototypes and used in 5GRAIL testing activities, also considering high-power UEs prototypes for field testing.
But the major achievement of this introduction plan was the availability of the FRMCS V1 specifications, included in CCS TSI 2023, aiming to deliver a system supporting critical applications (ETCS, ATO GoA2 and voice) using the RMR band. The FRMCS V1 specifications were partly validated in lab and field conditions, by the DG CONNECT funded 5GRAIL project.
2.1 FRMCS V2, the Next Steps
The approval of FRMCS V1 specifications has been concluded with the addition of them in the CCS TSI 2023 confirming FRMCS as a subsystem of the ERTMS [1]. FRMCS V2 is in progress to provide together with 3GPP R18 features, a complete FRMCS system to be tested during MORANE-2 European trial, which is expected to focus on field tests with conventional and high-speed lines and under cross-border conditions.
MORANE-2 is a major step that will provide to the railway operators with the first pilot schemes for FRMCS first deployment.
3 5GRAIL’s Outstanding Achievements, as First FRMCS Demonstrator
The scope of 5GRAIL was to validate FRMCS V1 specifications by defining functional end-to-end tests for a selected subset of FRMCS V1 features to be executed in lab conditions in Hungary, led by Nokia and in France led by Kontron also in field conditions in Germany, led by DB and in France, led by SNCF. The outcome of them considered as the first FRMCS demonstration provided feedback to the FRMCS V1 specifications, as part of the loopback process but also initiated or enhanced requirements in 3GPP specifications. Moreover, it is considered as an important step for the preparation of FRMCS V2 specifications.
Below, some important achievements of 5GRAIL, impacting the specifications are presented.
3.1 Railway Emergency Communication (REC)
The REC is an extremely important communication in railway environment, used in emergency conditions. Therefore, it is considered as a high priority communication and has distinct means for set-up and presentation. REC was not completely specified in FRMCS V1 and the work will continue in FRMCS V2 in parallel with the 3GPP R18 enhancement. However, a thorough assessment of implementation options [4] has been performed and described in the UIC FRMCS FIS V1 specifications which concluded that the Ad hoc Group Communication (AHGC) method with Server based area definition and user determination without required affiliation is the most suitable one, whose target is 3GPP Rel-18. The dynamic area definition based on the initiator’s location and the selection and affiliation of the impacted participants (clients) according to their location is a new concept in MCX standards, more focused on the Public Safety Emergency call use cases.
In the framework of 5GRAIL, at Nokia’s lab in Hungary [5], the server-based approach with affiliation of the concerned clients based on their continuously updated location report was performed. Although it is not the final AHGC implementation, the role and requirements on the MCX server were very similar, hence interesting outcomes have been provided to the specifications.
3.2 FRMCS-GSM-R Interworking
GSM-R – FRMCS Interworking is an important functionality during the coexistence period of both technologies. The specification of the interworking function is an on-going working item in European Telecommunications Standards Institute (ETSI), so the REC test case performed within 5GRAIL in Nokia’s lab is a pre-standard one. It is worth mentioning that the scenario also covers the cross-border situation where neighbour networks have different technologies in use.
The main realization in 5GRAIL was to initiate a REC on the GSM-R network when in the FRMCS system a corresponding REC is established by the CAB radio. Inside Nokia’s Mobile Switching Center Server (MSS), the incoming MCX messages defined in 3GPP for Interworking are interpreted and mapped to the GSM-R messages used by a dispatcher originated REC call. The following set-up is used for this test (Fig. 2):
Trains crossing the border is an essential requirement for FRMCS for the deployment allowing trains seamlessly travelling between the different countries, as currently with the GSM-R system. The implementation of the cross-border is mandatory for the FRMCS to be included in the EU legal frame of TSI. Border crossing was starting to be specified during the preparation of the FRMCS V1 and the work will continue during the FRMCS V2, since it is a particularly difficult topic as it is impacting all the strata. Moreover, some roaming functionalities start to be developed in 5GSA (5G Standalone) ecosystem and were only existing in 5GNSA (non-Standalone).
Cross-border implementation in the scope of 5GRAIL was also a pre-standard one, with two different flavours tested. In Kontron’s lab, the multi-connectivity concept was used with the simultaneous usage of two 5G UEs by the On-Board FRMCS gateway of Kontron, achieving a seamless transition from the application point of view. In the same lab, the cross-border was also tested with the On-Board FRMCS gateway of Alstom applying the bearer flexibility with two 5G modems each one configured to a dedicated link and used by the application whenever operational with a given priority, preventing the application of any outage impact [6].
In Nokia’s lab, Ng handover was configured using two 5G core systems by Inter Access and Mobility Management Function (AMF), where the active data session was seamlessly moved between the two cores without interruption. Due to the 5GSA capabilities available for 5GRAIL, the two core systems were configured as an intra PLMN setup with one MCX server [6].
The following figure presents the set-up as implemented in both 5GRAIL labs (Fig. 3):
Major steps have been achieved with the finalization of the FRMCS V1 specifications and the first demonstration of them, thanks to the 5GRAIL project. FRMCS V2 specifications and the MORANE-2 will be a challenging and exciting work, leading to mature products ready for the FRMCS pilot systems deployment.
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5GRAIL: An EU-funded Horizon 2020 5G for Connected and Automated Mobility (CAM).
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4.
UIC FRMCS FIS Working Group: Annex A: REC implementation options, UIC functional interface specifications (FIS), pp. 58–71 (2023)
5.
5GRAIL WP3: 2.3 railway emergency call, deliverable D3.3 first lab test report, pp. 31–33 and 2.4 GSM-R Interworking, pp. 33–34 (2023)
6.
5GRAIL WP1: 3.10 Cross-border, deliverable 1.2 Test report conclusion from simulated/lab environments, pp. 57–71 (2023)
