Twenty five years ago, the operational telecommunications systems for the Channel Tunnel were being planned and designed. Radio systems were very important in this provision for, as well as providing continuous communication with the trains, there was need to reliably communicate with all the personnel who worked in the tunnel and to the emergency services who might need to venture inside.

Thought was given to the provision of the new GSM public cellular service (2G) but the cost of providing a system on the radiating cable with sufficient capacity to meet the perceived demand from the travelling public was seen as prohibitive. Being out of contact for the short journey time of less than 30 minutes was not seen as a show stopper.

In the intervening period, attitudes have changed and the public expect to be able to use their mobile phones wherever they may be. Both Paris and London metros have had to react to this demand and are equipping their tunnels with appropriate systems. It would be strange if the Channel Tunnel was not to be similarly equipped. How, therefore, to make a suitable business case and get a system implemented? This has been the big challenge.

Existing radio renewal opportunities

The track-to-train radio network in the tunnel is based upon the ex-BR Cab Secure UHF system and the general usage VHF radio network was bought as an analogue proprietary system. Both are now obsolete technology and need replacing with GSM-R. Planning this renewal started in 2009 and, during this process, the question of providing the public with mobile telephone facilities emerged yet again. By this time 2G was well established and 3G services were also widely available. Engineers realised that it should be possible to superimpose these services on the infrastructure being used for the new operational system.

The GSM-R system operates in the 870 – 930MHz band, roughly twice the frequency of the existing track to train radio, and thus the attenuation will be much greater. To avoid excessive use of repeaters, a new radiating cable of very high quality has had to be installed. This has been supplied by Radio Frequency Systems (RFS), a subsidiary of Alcatel-Lucent, and is positioned on the far wall of the running tunnels – the opposite side from where the present radiating cable exists.

The authority to proceed with GSM-R was granted in 2009 and the cable has been progressively installed during routine possession times. These allowed four to five hours per night on three days a week during the period January to May 2012 but only on one night per week from June to December. The cable is supported every metre and has needed 53,000 fixing points in each tunnel, no mean challenge.

With public mobile service provision in mind, the cable is designed to support both the 2G networks operating in the 900MHz and 1800MHz bands and the 3G service in the 2.1GHz band. The forthcoming 4G service (sometimes known as LTE – Long Term Evolution) is allocated space in the 2.6GHz band and this must also be catered for as it is due to commence in 2014. Thus public cellular services (GSM-P) in all three bands would now be possible, and the plan to provide these commenced in June 2011 with a contract being let to Alcatel-Lucent in France for the necessary design and turnkey work.

Dealing with International boundaries

The Channel Tunnel has always been a problem in determining where the France – UK boundary is to be located. Legally it is half way across but this makes little sense for engineering system designs. Discussions with the Regulators arrived at a pragmatic solution for public cellular provision with the south tunnel (normal direction France to England) being determined as French and the north tunnel (normal direction England to France) being allocated to the British.

Negotiations commenced with both the French and UK network providers to establish whether they would collaboratively join with Eurotunnel to provide a public mobile service. These have been far more successful in France than Britain and an agreement was signed in 2011 with Orange, SFR and Bouygues Telecom to equip the south tunnel. ‘Free Mobile’ will also join this consortium later on.

Discussions with the UK operators, Vodafone, O2, Everything Everywhere (the new consortium of Orange UK and T Mobile) and Three, have been protracted. The Olympic Games have held up a decision, but it is hoped that progress can now be made quickly. Thus the bizarre situation exists that the south tunnel currently has service provision but the north tunnel does not.

Solving the technical challenges

With the radiating cable installed in each of the running tunnels, the design for a combined GSM-R and GSM-P system could proceed. The contract with Alcatel-Lucent proceeded to a fast timescale with the intention of having a service operating prior to the London Olympic Games. This required the design for the overall configuration and the supply of the necessary equipment to be completed by July 2012.

Each tunnel has two BTS (Base Transmitter Station) sites. These will be the equipment rooms sited at the shaft surface location some three kilometres from the tunnel mouths. In these rooms the transmitting equipment for both the operational railway (GSM-R) and for each network provider will be located. Feeder cable is run down the shaft to connect to the radiating cable.

Repeaters are required at 750 metre intervals in the tunnel, these being located in the central service tunnel and connected via feeder cables routed through the tunnel cross passages known as adits. A separate repeater is required for each of the GSM-R and GSM-P services. Power for the repeaters is taken from Eurotunnel’s safeguarded supply. The repeaters are two way – thus amplifying both the transmit and receive signals – and cover the 900MHz, 1800MHz and 2.4GHz bands. Band pass filters prevent unwanted interference from impacting on the particular service provision.

The provision of the repeaters has been sub contracted to a UK firm, Axell Wireless from Maidenhead, which has an internationally-recognised expertise in radio repeater technology. Additional repeater equipment will be necessary for the 4G service but this will need to establish itself with a large enough customer base before extending the service into the Channel Tunnel becomes justified.

Each tunnel will have six cells each of nine kilometres length. For every user, a potential bandwidth of minimum 384kbit all along the tunnel is available that will allow good speech communication and a usable data rate for mobile devices to connect to the internet. Once established, it is anticipated that the 3G service will be able to offer a maximum data rate of 8Mbit to a user and an average rate of 3Mbit. Thus the data service offering inside the tunnel is likely to be better than that in the normal outside environment.

Usage, maintenance and other technologies

The south tunnel service was introduced in late July 2012, just before the start of the London Olympics, and it is still too early to predict what the take up rates will be. Aimed at both Eurostar passengers and those travelling in cars and coaches within a Shuttle train, it is possible that demand will exist for several hundred simultaneous conversations. The worst case scenario will be with two trains in a single cell area, both of which are stopped because of an operating or signalling problem in the tunnel.

In such circumstances, it is possible the system will overload and in anticipation of this, the Eurotunnel operators may seek to use the SMS service to give a general message update on the situation. No special equipment is being provided on either the Eurostar or Shuttle trains. Users will communicate with the system directly by the on-air connection and thus the transmit signal from the cable and the receiver sensitivity of the system have to be good enough to overcome any attenuation caused by the metal cage of the train carriages. The offering is therefore no different to using a mobile device in open country and no special tariffs will apply.

The total cost of the project is €14 million for both tunnels, the majority of this being borne by Eurotunnel who have provided all the radiating cable and the equipment needed for GSM-R. The mobile network providers’ contribution is the supply of BTS equipment, the repeaters needed for their own service provision and the connectivity to their main network nodes.

An overall maintenance contract has been negotiated with Alcatel-Lucent but, with its high security requirements, the maintenance of the tunnel-mounted equipment is subcontracted to Eurotunnel which has needed to train their engineers and technicians for the combined cable and repeater system. However, with the BTS equipment located at the shaft top sites, the contract with Alcatel-Lucent will allow their staff access for both routine maintenance and fault rectification. The Service Level Agreement (SLA) calls for 99.5% availability with a 6 hour return to service when faults occur, and should either Eurotunnel or Alcatel-Lucent fail to achieve this, then penalties will apply.

It is perhaps ironic that the catalyst for the project – the provision of GSM-R – is not due to be commissioned until 2014, it being necessary to tie this in with the fitting of radios to the trains that operate in the tunnel. The GSM-R system will therefore have had a good soak test on its infrastructure before being brought into service.

One unknown is whether the Eurostar train provision of an on board WiFi service, let as a three-year contract to Nomad Digital in September 2011 to equip the trains, will be modified to permit the on- train network to communicate with the 3G service. It is not Eurotunnel’s intention to extend the unlicensed WiFi service in the 2.4Gbit or 5Gbit bands on to their infrastructure.

All looks set fair for the future. This project is another small step in the concept of having mobile coverage available wherever you are in the world, something that could perhaps never have been envisaged when cellular radio first started in the early 1980s.

Thanks go to Laurent Zimmermann and Stephane Popiolek from Alcatel-Lucent and Michel Boudoussier and Christian Rémond from Eurotunnel for their help in preparing this article.