The increase number of vehicles on roads and the immense number of fatal accidents they cause have driven the research and development of new generation technologies to help drivers travel more safely. One major cause of traffic accidents is that drivers cannot consistently respond to the changing road conditions appropriately. In fact, most accidents could be avoided if drivers could obtain and use relevant information of the traffic that is beyond their vision using wireless communications technology.
Recently, the IEEE community adopted the IEEE 802.11p standard as a main technology for VANETs. To test the feasibility of this technology, most researchers use simulations to evaluate its new applications and protocols due to the prohibitive cost of implementing real VANET setup. Therefore, we first analyze VANET’s wireless channel analytically and by simulations to predict its most appropriate propagation model and the communication range that minimizes the impact of the hidden terminal problem. Second, we derive a new mobility model that takes into account the vehicle’s follow-on safety rule, to accurately derive the
relationship between vehicle’s speed and network density. It is expected that broadcasting and multi hop communications will be dominant in VANETs safety applications and protocols. Therefore, a Network Topology p-Persistence (NTPP) scheme is proposed to alleviate the impact of the broadcast storm problem. NTPP is based on vehicles’ knowledge of their neighbors in their range and traffic parameters to reduce the channel contention, redundant re-broadcasts and message travel time and to increase the emergency message reception rate.
We analyze the reliability of the IEEE 802.11p in VANETs safety and warning applications scope taking into consideration different factors. It is shown analytically and by extensive simulations that the current DSRC specifications may lead to undesirable performance under harsh vehicular environments. Therefore, a novel Distributed Multichannel and Mobility Aware Cluster-based MAC Protocol (DMCMAC) is proposed to alleviate the impact of the hidden terminal problem, increase the network capacity and reliability. Cluster heads in DMCMAC are elected and re-elected in a distributed manner according to their relative speed and distance from their cluster members. The high stability of DMCMAC results from its adaptability to drivers’ behavior on the road and its learning process to predict the future speed and position of all cluster members using the fuzzy logic inference system. The reliability of DMCMAC is analyzed and compared with other protocols. It is shown by simulations that DMCMAC has high stability, its performance exceeds other protocols and can achieve a timely and reliable delivery of emergency messages to their intended recipients which make it more suitable for VANETs. iv
Design and Analysis of an Efficient and Reliable Mac Protocol for Vanets
