Wireless Local Area Networks (WLAN)

The emergence of the Wireless Local Area Networks (WLAN), such as Wi-Fi IEEE 802.11a/b/g/n, leads railway operators to rely on the potential of these inexpensive systems for control and command applications. Specific protocol layers for mobility and safety management in addition to a suitable radio engineering have to be implemented to ensure safety and security of operations. These systems are mainly deployed for metro applications (New York, Marmaray, Beijing, Shanghai) [3].

Finally, we can focus on the IEEE 802.11p standard which is an approved amendment to the IEEE 802.11 standard to add Wireless Access in Vehicular Environments (WAVE) [43]. It defines enhancements to 802.11 required to support ITS applications, including data exchange between high-speed vehicles and infrastructure in the licensed ITS band of 5.9 GHz (5.85-5.925 GHz). The IEEE 802.11p relies on a fast adaptation to rapid changes occurring in a highly mobile vehicular network, specifying a set of parameters for the the handoff process.

The IEEE802.11p has been experimented in urban railway transports, for CBTC applications [44] or Passenger Information System (PIS) for instance [45]. However, a recent paper [46] highlights that WAVE is largely developed for vehicle applications but few for applications in the railway domain. In this context, safety has to be considered with highest priority. Specific protocol architecture and technical considerations are presented in the paper to use IEEE 802.11p standard in the railway context.

The initiative to make the use of 5.915-5.935 GHz official for CBTC was pushed by UITP, RATP, STIB, ALSTOM, SIEMENS, and relayed by European Telecommunications Standards Institute (ETSI) to the European European Conference of Postal and Telecommunications Administrations (CEPT). This is conflicting with the request of ITS for the same band. Moreover, the study of using ITS protocol through 802.11p for CBTC does not seems to be fruitful.

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