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Wireless technology takes off in Asia: with new technologies placing ever greater demands on railway communication systems, wireless networks are proving an extremely popular means of transmitting data. Wolfgang Siemens and Andreas Kister of Siemens explain how wireless networks can support an array of applications under even the most challenging of conditions
By mobile | November 28, 2007
Increasingly, moving block train control systems are being used, operating as communication-based train control (CBTC) systems. Modern CBTC systems require up to 1Mbps (megabit per second) of uninterrupted communication between the trackside automation equipment and fast-moving trains.
Because most rail operators in Asia demand a high local content, it seems appropriate to use international radio standards and commercial off-the-shelf radio components, which can provide the necessary bandwidth. This is generally achieved by using standards and technologies for wireless local area networks (WLAN), and typical CBTC systems are based on the well-known 802.11b standard.
However, automation applies to more than just train operation. In driverless or even unsupervised transport systems, complex automated monitoring functions are also needed, demanding a sizeable bandwidth for communication between the vehicle and trackside infrastructure. The maintenance management of rolling stock, for example, requires at least the intermittent information transmission of large quantities of data for remote diagnostics and remote maintenance. Voice transmission for safety and convenience functions requires approximately 1Mbps of communication bandwidth within a radio cell.
A further example is on-board CCTV surveillance using cameras and a control centre. WLAN-based systems, such as those based on IEEE 802.11g, are currently favoured for such applications.
Here too, operators of complex and comprehensive supervision systems are increasingly supported by intelligent video functions with an increasing degree of automation that means a greater demand for bandwidth.
With the rapidly-growing prosperity of many Asian cities, passengers are demanding greater levels of comfort. This means the transport services provided for the passenger must quasi-automatically include a level of information and entertainment uncommon in Europe. While in Europe the concept of a passenger information system (PIS) refers to the time-honoured mixture of departures and arrivals, connections and alternative services, in the Asian market the term tends to be applied to multimedia entertainment.
Classical passenger information systems require approximately 0.5Mbps of continuous and uninterrupted communication between trackside installations and moving trains, but for multimedia systems, a minimum of around 2Mbps of uninterrupted bandwidth is required. There is also a need for additional intermittent data transmission for applications where information changes at a slower rate.
In addition, there is a growing need for individual passenger information and entertainment, for example through individual internet access.
Broadband platforms
The multitude of parallel applications can only be properly handled with a generic software architecture and a modular platform approach, which today’s standard WLAN products cannot offer. The general cost pressure also makes it necessary to operate the various applications outlined above with an integrated multi-application communication system.
Also, more and more channels will need to be occupied within the standardised frequency bands to obtain a sufficient overall bandwidth. Future multi-radio communication platforms will be able to utilise the bandwidth of a number of radio channels of the same technology in bunched mode.
In addition, the various requirements and the foreseeable demand for maximum bandwidth result in the development of multi-standard communication systems (also called hybrid systems), which integrate and use a number of radio components of different technologies or frequencies simultaneously. The data to be transmitted for the wide variety of applications is, in the case of hybrid systems, distributed dynamically among the channels and radio technologies available at that point in time and suitable for the relevant data.
Topics: Communication Technology |
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