Carrying CBTC data over a public LTE network: fact or fiction?

8 December 2015  •  Author(s): Carlos Rodríguez Sánchez & Juan Moreno García-Loygorri

For Eurotransport, Metro de Madrid colleagues Carlos Rodríguez Sánchez and Juan Moreno García-Loygorri, take a look at the feasibility of carrying Communications Based Train Control (CBTC) data over a Long-Term Evolution (LTE) network. CBTC data is mostly critical, but most of the services carried over mobile networks, like LTE, are absolutely not critical. This article1 provides an overview of the challenges that imply the CBTC communications subsystem, and the requirements for the mobile network, plus a description of LTE technology and railway-related aspects.

Carrying CBTC data over a public LTE network

Metro de Madrid is one of the earliest adopters of both CBTC technology and train-to-wayside broadband communications, with three lines equipped with CBTC technology and more than 150km of track with broadband connectivity.

CBTC is a state-of-the-art signalling technology for mass transit lines which offers the best transport capacity with the highest level of safety2. It is a very complex technology, with many subsystems and, therefore, with many challenges that need to be properly addressed. One of the most significant is the radio subsystem, an aspect that traditionally relied on commercial-off-the-shelf devices, mostly based on the IEEE 802.11 standards family. CBTC technology has achieved great success in the last 10-15 years and has a great future ahead.

On the other hand, LTE is a fourth-generation mobile communications technology standardised by the 3GPP and widespread all over the world. Its own name, ‘Long-Term Evolution’, clearly states its purpose of being a durable technology. It has an open and flat architecture, intended to suppress bottlenecks and provide low end-to-end latencies. Recently, both technology vendors and railway operators have shown some interest on LTE for railway use3,4,5, and the UIC has identified LTE as the key technology for train-to-wayside communication6.

The key point of this paper is to discuss the feasibility of carrying CBTC data over an LTE network. The LTE network could be a public one (owned by a mobile operator) or entirely private (property of the transportation authority or the operator) and some technical, operational and even legal issues should be addressed here. We try to answer this question with the help of our expertise in this area and some field measurements carried out recently.

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One response to “Carrying CBTC data over a public LTE network: fact or fiction?”

  1. David Rothbaum says:

    Interesting article. Indeed LTE spectrum is the major stumbling block. With enough effort a solution can be found.
    Ericsson will be presenting LTE for railways and metros at Mobile World Congress 2016. CBTC will be one of the first use cases adopted in the industry.

    Although I work for Ericsson, these opinions are my own.

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