RTR 4/2010 35 Fast, wireless communication along the whole length of trains Nowadays, high-speed data communication is regarded as axiomatic in many fields. That makes it all the more surprising that wireless technology tends to be generally ignored in designing even the latest generations of trains. Industrial Networking Belden Product manager, Hirschmann™ range, D-72654Neckartenzlingen olaf.schilperoort@belden.com Olaf Schilperoort Fig. 1: Equipment for WLAN communication inside a train (AP = Access point) ble to adopt an extremely robust design for the plugs and sockets for the cable connections that are intended to be routed through couplings. That explains why nothing more advanced than digital bus technology is to be found in trains today – or, at best, Ethernet technology in a modulated form making use of UIC cables. In the field of industrial automation, Ethernet has now been displacing the legacy bus systems for several years. Bus technologies are technically relatively simple and very reliable, but they do not support networking and are not compatible with one another. Ethernet has the advantage of being the facilitator that first brings the individual subscribers together in a network. Moreover, it uses a standardised technology (IEEE 802.3) and can thus be retrofitted for comparatively little cost anywhere in the world. Networking via Ethernet not only makes high data rates possible, but also the rapid recognition of the composition of the trains and many other functions as well. However, the fastest transmission of data through train couplings that has been possible to date has been 10 Mbit/s. It seems so obvious to look for the solution in the form of wireless networking. 2 Wireless networking along the entire length of a train Wireless LAN (WLAN) satisfying the IEEE802.11 standard represents the wireless version of the Ethernet network (Fig. 1). Here is a situation that any frequent traveller waiting for a train is familiar with: the train, to be fair, arrives on time, but then an announcement comes over the publicaddress system informing those waiting that the train is not running in the order advertised. It might even happen that individual coaches are not running at all. The outcome of this is that passengers first of all look up and down the platform then wander to and fro inside the train, facing a lot of bother in trying to find their reserved seats. If the relevant coaches are missing, the seat reservations will be missing too. The underlying cause of this is the almost total lack of flexibility in the technology used onboard. Once the individual coaches have been marshalled into a train, it is then impossible to change either the coach numbers or the seat numbers. For whatever reason, a train might find itself running backwards. If so, things will stay that way right through to the other end of the country. It is impossible to make subsequent changes to the numbers of coaches or seats. Those customers who are used to today’s Ethernet technology and the capabilities of flexible programming will justifiably start wondering why it should be that in highspeed trains, of all places, such capabilities should be apparently impossible. 1 Ethernet onboard If broadband Ethernet were to be installed inside trains, it would be possible to make realities out of many other applications too – similar to the situation that airline passengers, for example, now take for granted. This includes an onboard entertainment programme, featuring a choice of films available on demand, and, in the case of trains, could extend to access to e-mails or the internet from one’s seat and the latest information regarding connecting services, delays, and so on. With a broadband network, train crews would be able to provide an improved service, because they would have a central overview of the occupation of each coach. Security and safety could both be enhanced too through closed-circuit television monitoring and fast-acting emergency-call services. Up until the present, however, the only technology installed on trains has been hard-wired. The two explanations for that are the robustness and longevity of such systems. The biggest barrier to any form of broadband data communication within a train and the most serious bottleneck for it lies in the couplings between the coaches. These are the most severely stressed link in the whole communication chain. Couplings are subject to the heaviest wear of anything. Fluctuating temperatures, precipitation, contamination in various forms and even impacts by stones make it indispensa-
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