FRMCS, a key for ERTMS and rail digitalisation

(photo Bombardier)

GSM-R has become obsolete and is no longer the future of railway data transmission. FRMCS will have to replace it, taking into account the latest global data transmission standards.

As it knows, the GSM-R, the telecommunications element of ERTMS, has been a great success with its deployment on more than 150,000km of track in Europe and 230,000km worldwide. However, GSM-R provides seamless 2G+ connectivity between track side and on-board, but this GSM-based technology is nearing the end of its life while GSM-R sub-systems face obsolescence. GSM-R lacks the capacity to transmit huge amount of data needed today and in the future. Although the suppliers have guaranteed continued support for GSM-R technology until 2030, it’s time to reach a new data transmission technology.

That’s the reason why the International Union of Railways (UIC) started the first studies for a successor to GSM-R in 2012. In recent years, the UIC has brought together leading European railway associations and railways as well as the telecoms standardisation bodies ETSI Technical Committee for Rail Telecommunications (ETSI TC-RT) and the 3rd Generation Partnership Project Technical Specifications Groups (3GPP). 3GPP is a consortium created in December 1998 with seven telecommunication standardisation bodies such as: ITU (International Telecommunication Union), ETSI (Europe), ARIB/TTC (Japan), CCSA (China), ATIS (North America) and TTA (South Korea). This consortium produces and publishes the technical specifications for 3rd (3G), 4th (4G) and 5th (5G) generation mobile networks.

Don’t forget the rail
3GPP standards are structured as releases. Discussion of 3GPP thus frequently refers to the functionality in one release or another. Each release incorporates hundreds of individual Technical Specification and Technical Report documents, each of which may have been through many revisions. Current 3GPP standards incorporate the latest revision of the GSM standards. We are today on the 16th version, called R16. An R17 release is currently being developed and is planned for 2022.

(photo Global Rail review)

When developing standards at such a high global level, it is crucial to take into account railway requirements, as telecommunications affect very large sectors, such as aviation, shipping and industry, with the risk of forgetting the railway. Therefore, a lot of lobbying was needed to integrate the specific railway requirements by the 3GPP normative specifications. In fact, ETSI plays a key role to fit rail specific technologies into the mainstream worldwide mobile communication standards. The use cases were submitted towards 3GPP Working Groups, where a gap analysis with the existing 3GPP requirements is conducted and then the closing of the resulting gaps with additional or new normative requirements, which will be included in R17.

(photo Global Rail Review)

Introducing 5G technology (Release 16 or 17) provides a series of specific opportunities (1):

Enhanced spectrum efficiency – GPRS already represents a meaningful step versus circuit‑switching logic, multiplying up to four times the spectrum efficiency; further meaningful enhancements are expected with 5G
Overcoming the dual voice-data system currently in use, which complicates the whole architecture and significantly increases the on-board costs. However, defining an ad hoc on-board ERTMS and radio architecture for retrofitting and for new vehicles will be crucial to seize this opportunity
New features synergic with the introduction of the ‘game-changers’ for the Command, Signalling and Control systems of railways (notably, but not exclusively, ATO), including video communication for degraded conditions
High cyber-resilience and disposing of a reliable technology for high-speed and very-high-speed (up to 500km/h).

Unavoidable 5G
These developments have led to develop the Future Railway Mobile Communication System (FRMCS) as a worldwide standard for railway telecommunications. But that means also that rail operators should start to plan how they will prepare and migrate their networks.

Because of its low throughput (despite the major advance brought about by the arrival of GPRS), GSM-R with his 2G technology is often considered to be the limiting point of the ERTMS system. The question then arose of replacing the GSM-R protocols with another type of more efficient connectivity. The latest thinking of the UIC and the European Railway Agency (ERA) shows a clear preference towards 5G, a choice supported – isn’t a surprise -, by many telecom suppliers and major European railway operators. In fact, the 5G technology is the base for the new FRMCS standard, but 5G is also necessary for the digitalization of the railways. However, railway undertakings will have to retain their own mobile networks, as mobile operators have excluded the use of their commercial networks for legal reasons. The use of 5G allows an increase in throughput, a decrease in latency, a standardization of protocols that will be adapted to other markets and also a diversification of the competition. Above all, it promises a more reliable network with a high level of commitment.

The urgent need to develop a standard based on 3GPP specifications as described previously (Release 16, or higher), compatible with the harmonised band made available for GSM-R (900 MHz), is required by the revision of Commission Regulation (EU) 2016/919, planned for 2022 and which must to include this new norm and the FRMCS and other innovative functionalities, to update and enhance the performances of ERTMS and facilitate its deployment.

(photo Unife)

The FRMCS architecture
Considering the – yet unknow – increase of mobile communication demands in railways, it is required that the FRMCS concept shall be very flexible, in terms of bearer technology independency in such a way to be immune from the dramatic evolution of the telecom sector, scalable, expandable, and finally more sustainable from the economic point of view. This requires a state-or-art architecture which does not only include the latest technologies, but also allow the introduction of future technologies. While GSM-R is an inflexible system as it is treated as one block, FRMCS will decouple applications, services and transport to allow more independence and transport bearer flexibility. That means move from a voice-centric to a data-centric approach. This is where we see the importance of 5G. Decoupling allows more services – there are currently have some restrictions when using public networks -, and FRMCS will also give more flexibility for interoperability. The definition and introduction of FRMCS will cope with these trends, providing sufficient flexibility in terms of functionality, capacity and performance, and allowing cost reduction by using commercial mainstream telecom technologies, products and/or services, while keeping interoperability, which is the key for an integrated European railway area.

This modularity makes it possible to distinguish and separate critical functions (related to traffic management and train integrity) from ancillary « non-critical » functions, such as on-board passenger services.

Security
FRMCS will need to have dedicated spectrum available for critical applications. Railways’ needs for train performance and intelligent infrastructure must also be covered and will turn out to be far more significant in quantity than current ones. The critical FRMCS applications, together with their technological options, are mainly related to communication functions (voice and data) strictly linked to railway operations with safety implications.

FRMCS is therefore a highly flexible and modular architecture that can work with a variety of access technologies, including cabled Ethernet, Wi-Fi, point-to-point wireless, as well as LTE/5G cellular radios. The 5G used for FRMCS is a cloud-native architecture, thus virtualized and modular for much greater scalability and a wider range of services. The 5G network is software-driven and programmable, which makes it far more automatable and far easier to introduce new applications. This means it can leverage existing connectivity investments and will be able to evolve as new forms of access arrive. Advantages for railways are that FRMCS provides not only the same functionalities as GSM-R – train radio voice applications and ETCS data -, but can be also an ERTMS game-changer, for example for railway digitalization.

This is a crucial element in making the railways a sustainable transport of the future.

(1) Extract from Global Rail Review