Long distance train operators across Europe have been looking to compete with short-haul airlines to attract business travellers for several years. Their competitive pitch has been that trains are more convenient because they take a passenger from city centre to city centre, have less stringent security procedures and passengers can use their phones, tablets and dongles on the journey.
Achieving that ubiquitous connectivity, however, is not so straightforward. Such long distance trains routinely travel at speeds of up to 300kmph, and their modern carriage construction – typically of aluminium – creates a Faraday cage through which wireless signals cannot transmit. In addition, they often cross borders, meaning that the system must switch frequency bands and enable smooth roaming, and run in environments of hot and cold temperature extremes.
‘There are several aspects to the technical challenge,’ explains Samuel Buttarelli, director of sales for distributed coverage and capacity solutions for Europe at CommScope. ‘High speed trains in Italy and Switzerland travel at 300kmph and the Faraday cage situation poses challenges, particularly in new generation train carriages,’ he says. ‘New trains have even more shielding. For example, it’s normal to use metalised window glass. The challenge you need to address with whatever system you put on board the carriage is you need backhaul to move traffic. Clearly, for a moving train you can’t use fibre to achieve that so your options are limited to using 3G networks or satellite for backhaul.’
3G backhaul involves placing antennas on the top of the train to communicate and manage the traffic back to a cellular operator’s network using 3G as the bearer. The antenna must have the ability to connect with base stations along the train’s route and incorporate complex algorithms that allow the antenna to adapt its signal amplification from the point at which it links to a distant base station to the closest point at which it passes the base station – where the gain will need to be reduced – and back again as the base station recedes and the train hands off to another base station. At 300kmph, that transfer and adaptation is continuous. In order to provide sufficient capacity to passengers, each carriage typically has its own antenna.
The situation is made more complex by the fact that multiple operators are usually involved, so the antenna will need to perform these calculations in relation to multiple base stations for each operator.
With satellite backhaul, the train normally has one more sophisticated antenna to serve all its carriages. Satellite backhaul requires more sophisticated tracking and the service provider typically uses a larger server on the train to enable localised caching of a large volume of content to cover periods when the train is unable to connect to a satellite, such as when it is going through a tunnel.
Tunnels are an issue for both technologies. ‘High speed trains typically pass through a significant amount of tunnels and when you’re inside one, satellite has obvious and severe limitations,’ adds Buttarelli.
‘With 3G, coverage can be brought inside the tunnel relatively easily using a radiating cable with optical repeaters.’
In the carriage itself, the environment can at least be simplified and standardised. ‘It does depend on the train configuration but, in general, we install a system in each carriage,’ says Buttarelli. That typically involves placing a repeater in each carriage that works in conjunction with a radiating cable – in the carriage ceiling, for example – to propagate the signal. ‘The repeater gets the signal from outside the carriage and brings it inside,’ thereby addressing the Faraday cage limitation, he adds.
For Ian Brown, CEO of Axell Wireless, which has more than 500 in-train systems deployed, the environment is complex. ‘The biggest challenge is the vibration,’ he says. ‘The train is constantly rattling so the equipment has to be designed in a certain type of chassis that can absorb that and remain in service for a long time. A train operator doesn’t want to be taking a carriage or train out of service to replace equipment.’
GPS technology is also required because it is important to know the exact position of the train. ‘Very important decisions need to be made,’ explains Buttarelli. ‘For example, when a train enters a station, the on-board system is switched off to lower consumption and hand over the train to the station system. High speed trains also cross borders and every country has different operators in different frequency bands, so knowing where it is means it can automatically switch from one system to another.’
Brown sees further value in GPS capability. ‘As well as being able to define where [the train] is so it can automatically retune when it crosses borders, the system can be used if a train operator hasn’t made an agreement with an operator in the country it is moving into to deny that operator access to the system,’ he says. ‘If the train operator doesn’t want to propagate the signal [of that operator] through its carriages it can filter it out. I haven’t seen that happen but the capability is there.’
Installation of in-carriage systems is now being done at the point of manufacture, says Buttarelli. He claims major train makers are now fitting systems during construction to ensure they are in optimum positions in carriages and the installation is discreet.
Brown also sees this happening but, given the long life of trains relative to communications technology, sees retrofitting continuing. ‘Increasingly train operators are ordering the technology to be installed when the train is built but we work with train operators to retrofit equipment,’ he says. ‘Retrofits are more of a challenge because the work has to be done with the train in service. You have to physically play with the infrastructure of the carriage so you need the manufacturer as well to do that. The equipment has to be compact as space is at a premium and sometimes equipment can be installed in part of the luggage shelf or under seats.’
With the appetite for providing passenger communications among train operators growing, future trains will likely be designed with space for wireless repeaters, antennas and radiating cables.