California Partners for Advanced Transportation Technology

This paper studies the design of ad-hoc Medium Access Control (MAC) protocols for a vehicle or the roadside to send safety messages to other vehicles. Such a protocol is needed by Advanced Vehicle Safety Systems (AVSS) and the national Dedicated Short Range Communications (DSRC) architecture. The problem is formulated to meet the communication requirements of vehicle safety applications and the DSRC multi-channel operation model. We propose several ah-hoc protocols, all based on the principles of repetition coding. Analytical bounds of the protocols' performance are derived. Simulations are conducted to compare the performance of the protocols in terms of probability of reception success and channel busy time. The best among the proposed protocols is shown to significantly outperform IEEE 802.11 MAC protocol in vehicle safety communication environment. We obtain the optimal relation between the performance and protocol design, in particular that of data rate and transmission power. The sensitivity of the protocol performance is tested under various communication conditions as well as vehicle traffic conditions. Feasible combinations of the communication and highway traffic parameters are found to meet specific performance requirements on communication.