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On track for rail support

Posted: 6 December 2006 | Thomaz D’Agostini Aquino (Chairman) and Philip Harley (Deputy Chairman), TETRA Rail Forum | No comments yet

Digital Mobile Radio technology is making its mark on the railways. Globally, operators are, in the main, selecting either GSM-R or TETRA for main line railways and TETRA for urban rail systems.

In Europe, the EU has long been concerned about inter-operability and the inefficiencies of multiple communications networks in adjacent rail networks. The EU has recommended the use of GSM-R for all main railway lines and each EU member state must adopt Interoperability Directive 96/48/EX into national recommendation. This directive does not apply to metropolitan railways in Europe.

Digital Mobile Radio technology is making its mark on the railways. Globally, operators are, in the main, selecting either GSM-R or TETRA for main line railways and TETRA for urban rail systems. In Europe, the EU has long been concerned about inter-operability and the inefficiencies of multiple communications networks in adjacent rail networks. The EU has recommended the use of GSM-R for all main railway lines and each EU member state must adopt Interoperability Directive 96/48/EX into national recommendation. This directive does not apply to metropolitan railways in Europe.

Digital Mobile Radio technology is making its mark on the railways. Globally, operators are, in the main, selecting either GSM-R or TETRA for main line railways and TETRA for urban rail systems.

In Europe, the EU has long been concerned about inter-operability and the inefficiencies of multiple communications networks in adjacent rail networks. The EU has recommended the use of GSM-R for all main railway lines and each EU member state must adopt Interoperability Directive 96/48/EX into national recommendation. This directive does not apply to metropolitan railways in Europe.

In other markets globally, TETRA is quickly becoming the technology of choice for the urban rail industry as well as for some freight railway networks.

One of the main reasons for the spread of TETRA in the metro and light rail markets is the adaptability and suitability of TETRA technology to these markets as well as the absence of interoperability issues. This suitability has not limited the deployment of TETRA, with Russia implementing TETRA along a main line rail between Moscow and St. Petersburg and in Latin America where TETRA has been selected by freight operators for spectral efficiency and commercial performance.\

Extra flexibility in the choice of the digital mobile technology has resulted in TETRA being selected extensively for metro and light rail operators in Europe for either green field or mobile radio network refurbishments. Projects under deployment include:

  • RATP, for the entire Paris metropolitan and commuter areas, where all metro and commuter trains, light rail trams and bus will be equipped with TETRA terminals as well as thousands of agents
  • London Underground – Connect, in which TETRA services will be delivered to all London Underground stations and TETRA terminals used all over the network
  • Copenhagen Metro and Dublin LRT, where TETRA is the sole mobile radio system
  • Madrid Metro, in which TETRA will replace both Train-to-Ground and Station Radiotelephony
  • Lisbon Metro is another example of a Metropolitan operator who is providing strong indications that it will be moving in the direction of TETRA as the preferred technology.

The interest in TETRA is not limited to continental Europe. The Dubai LRT has decided to implement TETRA and nearly all other metropolitan transport authorities in the region have requested or have already decided that TETRA will be their digital mobile standard to replace the existing analogue technology.

TETRA has been implemented in the rail industry in almost all major urban rail networks in Asia including Hong Kong, Shanghai, Taiwan and Seoul – the list goes on. The Delhi Metro has taken a significant step forward by implementing TETRA with both voice and data (associated with Automatic Train Protection) communications.

These days, with security as a primary driving force in operational voice systems the resilience and mission- critical features developed into the core of the TETRA, places this technology in a unique position to provide value for money in response to the rail operators’ most important requirements. Coupled with the early success of TETRA in the metro rail environment telecommunications integrators and manufacturers are quickly moving to evaluate new applications that can be added to the TETRA rail product portfolio.

TETRA is now the preferred technology for voice systems. Before it can be put forward as a viable standard for rail signalling systems, it may need further enhancements and will need to be validated to ensure signalling and data for rail is handled efficiently and securely. With positive feedback from TETRA manufacturers and users, a group of TETRA Association members led the creation of a specific study team aimed to analyse the suitability of TETRA technology for the transmission of critical rail data.

As a result of the interest earlier this year the TETRA Association announced a new initiative to concentrate on the analysis of enhanced and resilient voice and data services specifically designed to meet the communication and control requirements of the rail operators.

In addition to market size analysis, technical and engineering teams are planned in order to identify:

  • Rail requirements as far as voice and data are concerned, for both railways and metro networks.

The key voice features required for rail are the standard features available in Trunked Radio systems; Individual, Group, Broadcast, Priority and Duplex calls. Additional special call features for rail; Location dependant addressing and Functional addressing can be addressed outside the radio system or through a combination of user aliases together with GPS and dynamic regrouping.

In the case of data, taking ETCS level 2 as a baseline, the radio system data requirements are very modest. The radio acts as a transparent bearer for the signalling running at typically 4.8kb/s (9.6kb/s is in the specification but is not preferred).

Safety in an ETCS system is provided by an additional layer that sits between the mobile radio and the signalling called the ‘Euroradio’ layer. The Euroradio layer adds Forward Error Protection to the data being sent so that the radio infrastructure can remain relatively standard.

  • Safety concerns and associated validation processes and practices for transparent transmission of signalling data.

The intention of the development is to use existing validated standard systems (e.g. ETCS) to minimise the systems and end to end validation necessary for the appropriate safety case(s). It is the intention of the TETRA Rail Forum to mesh with existing systems and not create new ones.

  • Critical parameters for data transmission and system resilience, like handover time, call setup time, transmission delays and error rates.

Some key radio requirements for ETCS signalling such as Call setup <5 sec are easy to meet as they are written around the performance of GSM-R. Other parameters such as; Connection failure probability <10-3, BER 10-4, Maximum end to end delay 0.5 sec, Average end to end delay 500mS, Probability of connection loss 10-4, Maximum break during handover <300mS should be able to be met through careful selection of the appropriate TETRA standard and detailed attention to site engineering.

The issue of site engineering or deployment rules is common in the specification of GSM-R systems. For example, the size and duration of radio shadow zones is critical to the design. Similarly the development of similar rules for TETRA is possible without impacting the design of current equipment.

  • Regulatory concerns.

Any deployment in rail requires the development of a safety case. The safety case needs to address the concerns of the operator and the appropriate (national) safety regulator.

  • Identification of Tetra features critical to rail.

A clear picture of the critical parameters will allow rail operators to proceed with safer procurement and/or enhancement processes.

The work elements outlined only serve to ensure that TETRA can be analysed as an additional option to GSM-R as far as voice and signalling are concerned. The real challenge, however, is to improve the ‘Quality of Service’ (QoS) for rail and in particular address the issues related to:

  • High train densities and communications requirements in metro areas.
  • Call set-up times to improve signalling performance so that rail operators can safely run networks with reduced headways
  • Safety improvement in track maintenance and infrastructure areas with man-down facilities.
  • Automatic re-grouping of handheld or vehicular users based on their GPS location.
  • Use of the different communication modes to provide greater coverage at lower cost.
  • Development of strategies to enhance operation should there be a failure of the communications infrastructure.
  • Increase the ability of emergency services to work with rail in disaster situations.

The TETRA Association is planning to formalise a TETRA rail proposal to provide operators with new options in their technology decision. The newly formed TETRA Association Rail Group, known as the TETRA Rail Forum, will identify the specific operational needs for voice and data services, particularly within rail signalling, control and train protection. Its main objective is to analyse the technical interfacing needs of such applications and jointly develop guidelines and best practices for system integrators to deliver proven safe systems particularly for metro operations.

The TETRA Rail Forum is also expected to advise on possible needs concerning the development of new specifications or recommendations to pursue compatible solutions.

In order to move forward, the TETRA Rail Forum has recently requested suggestions on structure and the participation of organisations and people to lead the different key activities of:

  • Marketing – identifying the market size and value to proceed
  • Technical specification – developing the user & signalling requirement specification
  • Engineering – identifying the scope of changes required to the TETRA standard.
  • Regulators – advising and assisting on steps towards standardisation/validation.
  • Users – advising on worthwhile operational additions.

The Marketing Subgroup, which has already begun its activities, comprises representatives from the consultancy, manufacturer and integrator sectors.

It is expected to have a clear picture of the requirements, the impact on the TETRA roadmap and the amount of research and development commitment required, by 2008.