Performance Analysis of IEEE 802.11b DCF-Basic Access and RTS/CTS in CBTC Under Field Conditions

This paper provides performance evaluation of Communication based train control (CBTC) system in terms of extensive saturation throughput and average delay for both basic access and RTS/CTS (Request to send/Clear to send) access mechanism. An experiment is designed to simulate considering varying no of contending stations and slot transmission probability in CBTC under the Wireless LAN Medium Access Control (MAC) and Direct sequence spread spectrum (DSSS) PHY specification for the 2.4 GHz band. It is assumed the saturation condition where N no of stations are contending for one shared channel and each station always has a packet available for transmission. Slot transmission probability is considered as the probability with which a station transmits its packet in a randomly chosen slot. We have considered a specific case of constant back off window wherein slot transmission probability is only dependent on min contention window ( CWmin). All simulations have been performed under these assumptions.