Author(s)

C. Bantin

Abstract

Mobile IP networks, using wireless LAN (WLAN) technology, have recently been successfully deployed for communications based train control (CBTC) applications. Packet transmission networks are well suited to the data communications requirements of CBTC, and WLANs, using universal data packet (UDP) transmission, a simple send and forget protocol, are ideally suited for this task. Moreover, the 802.11 family of WLAN radio standards allows for several megabits per second of data transmission, whereas automatic control applications require at most 10 to 20 kb/s data links. This leaves ample capacity for carrying additional data to and from transit vehicles, and opens up the possibility of providing additional data services. Transit operators are becoming increasingly interested in utilizing this extra capacity for CCTV, voice and emergency response services. WLAN radios can carry varying amounts of data for these additional services from one CCTV signal plus voice and data for basic 802.11, to several high-quality video signals and voice circuits for 802.11g systems. 1 Introduction Within the past two years, two urban transport rail systems have gone into revenue service using radio-based communications to support automatic train control (ATC) operations with driverless trains. The first is the Las Vegas monorail [1] and the second is the Disney Resort Line in Hong Kong. These are the first such revenue systems in the world to utilize radio for their ATC operation. The radio networks are based on the IEEE 802.11 [2–4] WLAN standards for communication between the trains and the wayside. CBTC systems have a modest requirement for data rate but stringent requirements for availability and delay. The ATC equipment will communicate with each train by polling it and expecting a response within a certain amount of

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