Passengers travelling to Britain through the Channel Tunnel can now use their mobile phones to make calls and access the internet, following completion of a technically challenging project to deliver the service.
Eurotunnel and French mobile telephone operators Bouygues Telecom, Orange and SFR brought the optical fibre system into operation in one of the two rail tunnels on 25 July to provide uninterrupted 2G and 3G network coverage. The other tunnel, for UK-France traffic, will be covered by British telecoms operators after the Olympic Games.
Equipment supplier Alcatel-Lucent worked with teams from Eurotunnel and the three telecoms operators to deliver a wireless service that would work in a 53km tunnel at a depth of 100 metres below sea level.
The system they developed uses a leaky feeder cable for transmission, with optical repeaters installed every 750 metres. The equipment was installed in just 10 months, a remarkably short period, and the work was achieved in the confined environment of the Tunnel while a full railway service continued to operate.
Ensuring adequate signal strength proved to be especially complex. Not only do the trains occupy a large part of the tunnel as they pass through, but the isolating ‘Faraday cage’ effect means that radio signals are weaker inside them.
An Alcatel-Lucent spokesman said the radio signal had to be treated in a very specific way to obtain a good level of transmission quality, in particular inside the vehicle Shuttles. In the end the company’s engineers came up with a novel solution to ensure that the public and rail-specific radio systems (GSM-P and GSM-R) and another used by the Fire service would all work inside the Tunnel.
Twenty million people travel through the Channel Tunnel every year in passenger trains and vehicle shuttles.