The LHC goes 3G

A new telecommunications network has been installed in the LHC tunnel to facilitate operations during the long shutdown. Anyone using a smartphone, tablet or laptop computer will now be able to access the Internet from the tunnel.


Results of a download (green) and upload (yellow) test carried out in the LHC tunnel using the new Universal Mobile Telecommunications System (UMTS).

The first long shutdown has officially begun, and the teams are about to enter the various tunnels around the Laboratory. It’s a good opportunity to talk telecommunications. As you can well imagine, even the highest of high-tech smartphones remains stubbornly silent and unresponsive 100 metres below the ground.

Except at CERN… The IT-CS Group has implemented an impressive state-of-the-art solution to tackle this problem - a new Universal Mobile Telecommunications System (UMTS), better known as “3G”, covering the entire 27-km circumference of the LHC tunnel.

Established on the 900 MHz frequency, the network is freely accessible from telephones less than 2 years old (earlier models are not equipped to receive this frequency) and any laptop computer equipped with a CERN 3G key(1). “The UMTS is relayed by leaky feeders(2) already installed in the Laboratory’s tunnels,” explains the project leader, Rodrigo Sierra Moral (IT-CS). “They have been relaying the VHF, GSM and TETRA systems for many years [see the article on TETRA in Issue 51-52/2012 of the Bulletin].”

With a data throughput of 18 Megabit/second in the downstream direction (from the network to the user) and 5 Megabit/second in the upstream direction (from the user to the network) – at all points around the tunnel – this new system will make life considerably easier for the operations teams, enabling them in particular to upload data directly from the work site. Rodrigo adds: “The network should be operational by the beginning of April and will then be permanent.”

To improve data transmission rates, the IT-CS Group has also been modernising the VDSL (Very-high-bit-rate Digital Subscriber Line) infrastructure, those well-known “network sockets” located every 100 metres around the LHC tunnel.  “Using second-generation equipment, we have improved network performance nearly tenfold. Unfortunately, compatibility with the old VDSL/Wifi modem kits used during LHC construction couldn’t be maintained. We therefore kindly request that anyone in possession of these previous-generation kits returns them to the Telecoms Lab (Building 2/1-046),” says the leader of th project, Sébastien Ceuterickx (IT-CS). “To mitigate this compatibility problem, we will be deploying  more than 270 next-generation VDSL/Wifi emitters in most of the LHC tunnel for the duration of the shutdown. These emitters will provide a Wifi connection that is easy for anyone to use, offering performance levels ranging from 35 to 80 Megabit/second. But this Wifi infrastructure, available from April onwards, will have to be dismantled before the accelerator restarts as the modems will not withstand the LHC operating conditions.”

In parallel, the members of the IT-CS Group are already working on the future deployment of a 4th generation (4G) network, which will replace the current UMTS in 2018, for the second long shutdown.

(1)3G keys are available at the CERN Telecoms Lab (Building 2/1-046).

(2) Leaky feeder technology allows radio waves to be emitted in confined spaces such as tunnels.

by Anaïs Schaeffer