Communication Control

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Most European railways provided track-to-train radio systems during the latter part of the 20th century. Many were based upon the UIC (Union Internationale Chemin de Fers) Spec 751-3, prepared as an intended standard for all train radio systems across Europe. Not every country was able to adopt this specification mainly because of domestic radio licensing difficulties but Irish Rail (IR) did get agreement to use the 751-3 standard and its radio network has retained it since start-up.

Whilst the long-term intention is to move to GSM-R, there has been a need to upgrade the radio control equipment in order to extend the existing system’s life for a few more years. The challenge has been to find someone to build a new control package that would interface to the external radio base stations situated at the trackside that give transmit and receive signals to and from the trains.

Enter Frequentis, a company with its headquarters in Vienna that specialises in communication and information solutions for control centres dealing with air traffic, emergency services, railways and others. As well as producing the operational communication platform for new GSM-R networks across Europe, Frequentis claims to have the ability to integrate any existing communication infrastructure without necessarily having the engineering data of the system to be replaced. In short, they will work out the requirements and interfaces from first principles.

The Irish Rail radio network

Irish Rail entered the track-to-train radio club in 1984 when the UIC 751-3 system was introduced on the DART (Dublin Area Rapid Transit) line from Malahide and Howth in the north to Bray/Greystones in the south. This was a newly-electrified urban railway. The radio equipment was supplied by AEG-Telefunken from Germany and was broadly similar to that used by DB.

The system uses a four-frequency channel – three alternate transmit frequencies to the train and one common frequency from it – with four channels being made available in the 456-461MHz band. Reuse of the channels is necessary to get the complete coverage needed so channel planning has to be carefully done to avoid interference. The signal centre presentation was a standard AEG control unit.

Gradually the system has expanded to cover all but two routes on IR’s network, these being Tipperary-Rosslare and Ballybrophy-Killonan Junction. Base stations are connected to a common four-wire transmission line in ‘daisy chain’ mode, the lines being 2Mbit PCM circuits on a copper bearer or direct copper pairs.

Over time, the AEG control equipment became obsolete and a new control front-end was supplied in 2000 by EADS-Funkwerk, EADS being the successor company to AEG. Such is the march of technology that this too was becoming problematic to maintain and Irish Rail decided on a more adventurous upgrade in 2008.

Investing in a transmission network

By this time, IR had invested in a new digital SDH (Synchronous Digital Hierarchy) transmission network on fibre optic cables. This is formed in rings, thus giving greater resilience to the radio base station control circuits in the event of a cable cut. Where stub-ended lines exist then the ring formation is achieved either by –

•        a return cable on the opposite side of the line

•        a fibre cable installed (buried) on a disused line

•        microwave radio links to another node in the network.

Supporting the SDH core network are lower order Plesiochronous Digital Hierarchy (PDH) digital transmission systems that give circuit access to all radio base stations, passenger stations, level crossings and other depot locations.

A new control concept

With this resilient network in place, Irish Rail could be more adventurous with its control equipment philosophy and established a vision to combine all telecommunications applications, including radio, onto a single terminal for each operator. A functional specification was prepared and the requirement issued via an OJEC notice. A number of firms showed interest but in May 2009 the contract was awarded to Frequentis. The timescale for design and delivery was short so the company had a steep learning curve for this ‘Integrated Communications Terminal’ project.

The work involved understanding –

•        all the landline-based telephone systems to be incorporated – SPTs, block telephones, level crossing phones, dial-up admin telephones and emergency analogue lines

•        how the UIC 751-3 radio system worked, especially the emergency call, group call, data messaging and means of distributing calls to the correct signaller’s area of control

•        the IR geography and especially the routing and interface to the SDH/PDH networks and the connection to the ‘daisy chain’ radio line circuits.

With information on the existing networks being contained mainly within Irish Rail records (the original German suppliers having either gone out of business or having more modern equipment which superseded the original), getting precise details on what the various interfaces needed to be was quite a challenge.

frequentis irish rail radio control
A driver operates the in-cab radio equipment

Design, delivery and installation

Having understood what was required, Frequentis set about designing the new system based upon its family of Dicora terminals. All the central control equipment is located at Dublin’s Connolly Signalling Centre where the interface is made to the existing radio and telephone lines via new Line Terminating Units (LTUs). Replacing the multiplicity of racks needed for earlier AEG and Hörmann Funkwerk equipment are just two racks – to these are connected the signallers’ and regulators’ Dicora terminals on the operating floor of the IECC. These positions now have only a single terminal to replace the multiple combinations of terminals existing previously.

Whilst Connolly is a large centre controlling most of the Dublin suburban area and some main lines as well, there are still many other smaller signal centres or boxes around the country. Connolly is however the hub for all radio calls to and from the trains. When a call is received, the location of the receiving base station is known and the system will automatically re-route this call to a Dicora terminal in the appropriate signal box. This connection is via a 2Mbit transmission path over the SDH/PDH network. Similarly, if the signaller in a remote signal box wishes to call a train, they will key in the train’s calling number and this information is routed via Connolly out to the appropriate line where the train is known to be. Hence the importance of a resilient transmission network and the criticality of the SDH rings – without these having 100% availability, geographic areas of the radio system would be put at risk.

The control equipment has been manufactured at Frequentis’ Vienna premises and installation of the central control system at Connolly has been undertaken by the company’s staff. The Dicora terminals both at Connolly and the out station signal boxes have been installed by Irish Rail technicians.

Commissioning, handover and maintenance

Prior to anything being brought into service, a full FAT was carried out in Vienna. This identified a few gremlins that had to be corrected. With everything installed, the methodology for commissioning had to be determined. IR decided on a step by step approach – line by line and system by system, with first the admin phones, then the SPTs, then the block phones and finally the radio lines. A gradual changeover has thus been achieved, with the work being done at night.

Key to success has been the training of the signallers/regulators and maintenance staff. This was achieved by a training programme for nominated staff held at IR’s training school at Inchicore. Operations training took the form of a ‘train the trainer’ concept, following which all others were trained in a demonstration room set up in Dublin. This took some time (May to September 2010) as signallers from all over the country had to learn how to use the new terminals.

IR maintenance staff are also trained on the equipment and its connections, it being the policy to undertake all first-line maintenance in house. Frequentis give back up support as required.

frequentis irish rail rural signal box
Calls to the country's many rural signal boxes are routed from the hub at Connolly

Future radio plans

Irish Rail has achieved a complete modernisation of its radio and telecommunications operational control network. The radio base stations and indeed the train mobiles – the latter being various marques of AEG equipment – are unchanged. A useful life extension is the result, ensuring that equipment of ageing but reliable vintage can be married up to a modern control front-end. Track-to-train radio in Ireland is regarded as safety-related rather than safety-critical, with consequent simplification of the approval process. The project completion in a contractual time of 18 months is a remarkable achievement for both Frequentis and IR.

Irish Rail does not stop there however. Mindful that the rest of Europe is migrating to GSM-R, IR intends to follow this route as well. The plan will see the original DART network being the first section to change over, probably in two or three years time. This will free up mobile equipment from the electric trains to be used as spares for trains elsewhere. Devising the strategy for duplication of infrastructure or trains during subsequent roll-outs to GSM-R will need careful thought.

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