RF over Fiber Required for World’s Longest, Deepest Railway Tunnel

The Gotthard Base Tunnel is the world’s longest and deepest railway tunnel at 57km (35.5 miles), with up to 2,300 meters of rock cover. Taking over 17 years to construct, there were numerous challenges involved, including how to get PMR (Private Mobile Radio), GSM-R (Global System for Mobile Communications – Railway) and UMTS (Universal Mobile Telecommunications System) in the tunnel.

The communications services are needed for workers, train operatives and passengers to use their mobile phones for cellular phone calls/text messaging and 3G/4G mobile data.

In order for the GSM-R, PMR and UMTS base stations to operate they need to be provided with timing synchronization. Digital services provider, ATOS AG needed to get GPS signals from an outside, clear sky location into the tunnel to the base stations. ATOS solved the challenge by using ViaLite‘s RF over fiber GPS links.

The high sensitivity links allow the signal, which is very low at -110 to -130dBm, to be accurately transported over considerable distances; connecting high-gain ViaLite GPS antennas – located on the mountainside – to the base stations within the tunnel.

The ViaLite system used incorporates 3U rack chassis units and multiple levels of 1:1 redundancy to ensure five nines reliability; this is very similar to the ViaLite system in the London Underground which was installed in 2001/2. Gotthard Base Tunnel’s system also incorporates ViaLite ODE-A outdoor enclosures, which are used to house the GPS links above the tunnel; protecting them from the elements.

ViaLite Communications provided full on-site training to ATOS to allow them to install and service the GPS links in Switzerland, where the tunnel connects Ersfeld (UR) and Bodio (TI).

Neil Seager, Head of Sales at ViaLite, said: “This was a complex and challenging project and we were honored to be involved with ATOS in its delivery.”

The Gotthard Base Tunnel opened for full service on 11 December 2016.