Rail: Transition to 5G - Technical Viewpoints

The International Railway Union (UIC)

UIC, a world-wide railway association, is driving the successor of GSM-R for a new digital radio system: Future Railway Mobile Communication System.

FRMCS is an international programme for automated railway, where flexibility will be key, including the possible use of satellite where terrestrial networks are not feasible. The 10-year roadmap sees the implementation of pilots as part of the move towards greater digitisation and automation, an improved safety system and full interoperability.

3GPP brings the building blocks for FRMCS as part of the close collaboration between UIC, ETSI and 3GPP. 

Targets 

•  Digitisation and automation of the railway system and its operation require a broadband system.

•  The railway system must remain safety related. 

•  It must be interoperable between countries with seamless cross-border cooperation. 

•  FRMCS-GSM-R co-existence for about 10 years must be ensured.

•  Having a 5GS target technology that can allow for the integration of LTE and E-UTRA. 

Technical viewpoints

Mission-critical services with terrestrial and non-terrestrial networks - shift towards independence:

• Decoupling application stratum, service stratum and transport stratum.

• Removal of dependencies.

• Timely use of new access technologies.

 Transport bearer flexibility

• Vertical or horizontal (combined) use of various access technologies. 

• General simultaneous use of access technologies or depending on user location. 

• Extending flexibility and modularity for various operational scenarios.

Specification context 3GPP-ETSI-FRS/SRS-FIS with varying levels of specialisation

• Application-specific, including technical specifications from UNISIG for other functional applications. 

• Rail-specific: UIC FRS/SRS, including onboard. This reflects the view of the functional user requirements and provides the bridge for other applications.

• ETSI: generic normative technical specifications will sum up the necessary FRMCS building blocks for transport and services.

• 3GPP: normative technical specifications form the generic building blocks for transport and services. 

Challenge of limited spectrum

•  Limited spectrum availability during and after co-existence.

•  Channel bandwidth of 1.6 MHz during co-existence.

•  Channel bandwidth is not supported in 5G NR, hence narrow band approach.

 Challenge of the train life cycle (typically 30 years)

•  Decoupling application, services and transport to avoid re-certification for safety-relevant applications, e.g. ETCS, an on-board application. 

•  Multiple users on board have to share 2-3 UEs, hence gateway function between trains is required.

•  Regulated access between train and ground with the removal of unauthorised access.

•  Off-network (sidelink) to control the integrity of the train. 

Challenge: Positioning

•  Positioning balises mounted on the track will not solve train positioning in stations. 

•  Accuracy of less than 1m at speeds of up to 500km/h.

•  Multiple sources required. 

•  Position estimates have to be integer and need to fulfil SIL-4 requirements. 

Other challenges: with train speeds of up to 500km/h, radio access needs to provide robust channel estimation and robust transmission. 

Publications and videos

March 2019: UIC Future Railway Mobile Communication System: Use Cases

UIC video on the future railway mobile communication system (FRMCS)