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TETRA digital networks have become the natural choice for almost all new mobile radio installations in urban light rail and metro systems. Alun Lewis examines the reasons If there’s been one overwhelming force at work through the last 9000 years or so of human history it’s been the inexorable move of people from the countryside to cities. The usual disasters – flood, fire, war and earthquakes – may have caused the odd blip in the trend, but the direction has been overwhelmingly one way. Over the past century, that trend has begun accelerating sharply – and that in turn is now creating huge new growth for TETRA in mass transit and metro applications – especially in what used to be called ‘the developing countries’. According to the United Nations, we have just passed an important tipping point in human demographics, with more than half the total population now living in cities or urban areas. Add to that the fact that 80 per cent of that urban growth is happening in Africa and Asia and we start to see some of the potential here in what are often ‘green field’ projects, building on the already well-established use of TETRA in supporting European urban transport systems. A demanding environment Mass transit networks – essentially using packet-switching technology on humans – already use a variety of different systems including tram, overland train, bus, escalators, moving walkways and even that ageing symbol of the 21st century high-tech world, the monorail. In some parts of the world, many already have TETRA-based communications supporting them. It is, however, in the metro or largely underground-based systems that TETRA’s strengths and public safety heritage bring overwhelming benefits. For a start, just consider the physical environment that it has to operate in – as Markus Kalt, vice president for business operations EMEA for the radio infrastructure specialists Andrew Corporation, explains: “At its most basic, equipment that’s going to be placed in hot, damp and dusty train tunnels needs to meet environmental specifications like IP65 to ensure its operational integrity. “When metro communications systems are being planned, the overwhelming aim must be to keep the amount of physical infrastructure actually deployed in the tunnels themselves to an absolute minimum. Most metro systems only shut down for a few hours each night and the scheduling of maintenance or repair work must be fitted into these very narrow windows. A poor decision at the planning stage can have major repercussions further on in the project when the trains start rolling. “Similar issues apply to the siting of larger infrastructure items in the stations themselves, which are often long and narrow and present their own engineering and environmental challenges. “Finally there are the strategies of what types of antenna or radiating cables to use and whether different radio systems can be combined on to one cable.” Security and dependability While the ability to operate reliably in a ‘dirty’ environment – in terms of the physical, acoustic and electrical conditions in a tunnel system – is a major plus factor for TETRA, the vulnerability of Metro systems to accident or terrorist attack is well understood. Some systems have already been built that allow emergency service personnel to use Metro communications in the event of disaster. In the UK, where inquests into the victims of the 2005 London bombings are currently underway, a heavy focus has been placed on the failures of communications systems and the lack of compatible TETRA coverage in the tunnels. This made it necessary to manhandle cable into the tunnels so that emergency service workers could communicate at the scene. The problem was finally fixed in 2009 through an extension of the TETRA-based Airwave public safety network throughout London Underground’s 250 miles of track. Fortunately for the mass of the travelling public around the world, events like this are extremely rare – and it’s through TETRA’s role in improving both the cost-efficiency and the user experience of Metro systems that the benefits of the technology become most effective and widespread. Robin Davis, chairman of the TETRA Rail Forum and projects director at Actica Consulting, sets the wider scene: “For quite some time already, TETRA has been the dominant choice for the metro market segment to conduct station–train–control room voice communications. Features such as station call, role-oriented dialling and the newly introduced expedited handover facility have further increased the service levels that TETRA typically offers.” ‘Their eyes widen’ The drivers out there are already clear. And, for Per Skovsund, sales director at the TETRA specialist Damm Cellular Systems, two different types of migration are involved: “On one hand we have an increasing trend to urbanization across the developing world as populations move towards where the jobs and opportunities are. On the other – at least where some forms of mass transit already exist – there’s a parallel migration from older analogue systems to the digital benefits of TETRA.
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