Potential for wireless networking in trains

08 April 2011

Top-speed data communication is generally taken for granted today. This makes it all the more remarkable that even very recently designed trains pay almost no attention to wireless technology. Olaf Schilperoort, product manager Industrial Networking, responsible for Belden’s Hirschmann series, explains the difficulties that have to be faced and what shape a solution might take.

Frequent train commuters will know the situation: the train arrives on time, but even before it reaches the platform it is announced that the cars are not in the order shown. Sometimes there are even cars missing. The result of this is that passengers on the platform, and subsequently in the train, have extreme difficulty locating their reserved seats. When some of the expected cars are not included, the corresponding reservations will also be missing.
The reason for this confusion is that the

Onboard train technology still lacks flexibility. Once the elements of a train are put together the car and seat numbers are fixed and cannot be changed. If shunting considerations cause the train to leave the shed in the wrong direction, then it will remain the wrong way around until it reaches its destination. There is no way of renumbering the cars and seat numbers.

However, if trains were equipped with broadband Ethernet networking, it would be possible to implement this and numerous other applications that airline passengers, for example, already take for granted – onboard entertainment with a selection of different films that can be shown on request; access to e-mail or internet from the train; up-to-date information about connections, delays and so on.

A broadband network would enable staff on board to improve the service by providing a central overview of the occupancy of individual cars. Video monitoring and fast-response emergency services could also serve to improve safety.

However, trains today are still equipped with cable-based networking. There are two reasons for this – their robustness and their durability. Any broadband connection on board a train suffers primarily from the fact that each of the couplings between cars acts as a bottleneck, slowing down the data transfer. They are the most heavily used connections, and are subjected to much wear and tear. Changing temperatures, rain, snow and sleet, contamination with dirt, and impacts from loose chippings all demand the use of robust plugs and sockets for the cable connections that have to pass through the couplings. This is why, to date, trains have, at most, digital bus technology or modulated Ethernet using the UIC line.

Ethernet has the advantage over some traditional bus technologies by allowing the individual subscribers to be networked, and is also a standardised technology (IEEE 802.3), meaning it can be upgraded with additional modules anywhere in the world at relatively low-cost.

Ethernet networking not only permits high data speeds, it also facilitates fast recognition of the train configuration and is readily extensible. To date, however, connections through train couplings have – at best – achieved rates of 10 MBit/s.

A wireless network
Thus far, the WLAN standard has diversified into four variants, from the IEEE802.11b standard, offering gross data rates of up to 11Mbit/s, right up to the new IEEE802.11n standard, which currently offers up to 300Mbit/s, and is scheduled to reach 450Mbit/s in a subsequent stage. These rates are adequate for implementing the desired facilities and services in the train, and for future requirements such as electronic rear-view mirrors or front cameras to improve passenger comfort. A wireless network can be installed in an existing network – the existing cables and couplings do not need to be modified.

In practice, we find that there are some technical problems that remain to be solved even with a wireless LAN. Installing WLAN access points, and particularly antennas, in an existing train can be quite a challenge. Every bit of space is already taken up. Naturally, small, easy-to-install units will be advantageous here. A further advantage can be achieved by reducing the number of units required through the integration of more than one WLAN interface into a single access point. The units naturally also have to meet all the standards required for equipment that is installed in trains. These are stringent requirements, and cannot be fulfilled by just any device.

But the greatest challenge is caused by the simple fact that a wireless network has no external boundary. Electromagnetic waves do not stop when they reach the side of the train. Setting up a connection between two cars or train sections needs only to bridge a very short distance. It is particularly important to prevent two neighboring trains from setting up an unwanted connection. And, naturally, there have to be safeguards to prevent unauthorized persons from gaining access to a train’s internal network.

Modern WLAN equipment is perfectly able to meet these requirements. Authentication and encryption are mechanisms that are described in the WLAN IEEE802.11i safety standard, which is supported by almost all modern products.

The solution to the second task – setting up correct one-to-one connections between one train section and another – calls for equipment features above and beyond those stipulated by the standards. The embedded operating systems in the WLAN access points are capable of supporting the verification of connections, thereby supplying a certain native intelligence. With appropriate programming of the system, and powerful management software to monitor and control the wireless and cable-based network, the solution is as good as complete.

As a manufacturer of both industrial standard Ethernet hardware and powerful management software, Belden offers such complete solutions from its range of Hirschmann products. The management software uses LLDP to recognize the topology of the train’s on-board network. This information can then be used to flexibly assign numbers to cars, seats, etc. The industry’s tried-and-tested redundancy mechanisms reinforce the reliability of the network.

Hirschmann WLAN access points support all the usual rail standards, and also offer the very latest WLAN standard. This IEEE802.11n standard offers transmission rates of up to 300Mbit/s plus markedly increased transmission stability. A further benefit of a WLAN is the option of video transmissions.

This new standard is supported, for instance, by Hirschmann BAT300 access points/access clients, which are available in both IP40 and IP65/67 versions. The integrated multiple input multiple output (MIMO) technology ensures a stable radio connection even in the event of reflections or other forms of interference. The units possess a compact metal housing and can be used at temperatures from -30°C to +50°C or +55°C (BAT 300-F). This makes it possible to set up fast and stable infrastructure networks, wireless distribution systems (WDS), or point-to-point connections, even in harsh environments.

With an integrated IP router, it is possible to set up as many as eight subnetworks, which can be assigned to corresponding ports and interfaces in the access points / access clients. It is also possible to connect both analog and DSL modems, for instance for WAN routing or remote maintenance. Management functions can be carried out via the web interface, Telnet, TFTP, FTP or SNMP V2. The redundancy protocols Rapid Spanning Tree and VRRP ensure high availability of the network. Among other features, the quality-of-service functions specified by IEEE 802.11e provide for the prioritization of voice or video streams.

The use of Ethernet networks in trains offers numerous ways of increasing passengers’ safety, and convenience, and their acceptance of rail transport. Existing trains can also be equipped without needing to rethink or modify their cabling, which is a considerable potential advantage in terms of time and money when trains are retrofitted and/or redesigned. Combining a cable-based Ethernet network with its wireless counterpart can provide an elegant solution to one of the core problems of on-board networks for trains, namely the couplings between cars, but it is necessary to use robust hardware and industrial-standard management software for long-term, secure operations.

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