Performance Evaluation of IEEE 802.11a MAC Protocol for Vehicle Intersection Collision Avoidance System

Abstract

Vehicle-to-vehicle (V2V) communications network is a subclass of mobile ad hoc networks (MANET). With the new dedicated short range communications (DSRC) at 5.9 GHz, vehicles equipped with DSRC devices will communicate and collaborate to broadcast their safety-critical information to each other. DSRC is to be used in a wide range of advanced vehicle safety applications such as intersection collision avoidance system. The DSRC specification is based on the physical (PHY) and medium access control (MAC) layers of the IEEE 802.11a. The MAC mechanism for the IEEE 802.11a is the distributed coordination function (DCF), which is based on carrier sense multiple access with collision avoidance (CSMA/CA). Mobile nodes contend for the channel using a DCF random backoff timer. A random backoff algorithm chooses a Contention Window (CW) value between aCWmin and aCWmax. The random number, CW, is the number of time slots the mobile node has to sense the channel idle before it may transmit. In this paper, we developed an intersection traffic simulator to evaluate the settings of IEEE 802.11a DCF aCWmax on the available bandwidth per vehicle and on the required communication range. Our simulation results show that it is sufficient to set the aCWmax to 200 and the communication range to 200m for the intersection collision avoidance system enabled by DSRC.