Author(s)

C.C. Bantin

Abstract

C. C. Bantin Alcatel, Canada Abstract The Alcatel ComTrac DCS system uses open standards protocols. Of these standards, contention-based communications systems with guaranteed access and superior error management, are best suited to both the CBTC and the CCTV applications. ComTrac is based on the Ethernet family of network standards, with IEEE 802.3 for the wired portion and IEEE 802.11 standard for the wireless portion. Within this wireless standard, frequency hopping spread spectrum (FHSS) is preferred over direct sequence spread spectrum (DSSS) because of the superior interference immunity and the ability to co-locate several access points. In the network design, priority is given to the CBTC communications requirements. Based on a typical system, an 802.11 transmission rate of 1 MHz can support more than 10 trains simultaneously through any access point. The minimum bandwidth requirement is 25 such channels of 1 MHz each (in a frequency hopping configuration) for a total of 25 MHz. This wil

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