Research On Emergency Warning Messages Dissemination In Vanets

As an important component of Intelligent Transport System (ITS), Vehicular Ad-hoc Networks (VANET) attract increasingly more attention for its applications in preventing collisions and accidents of vehicles. VANETs mainly utilize inter-vehicle communication to inform the rear drivers about the dangers in front. This can help to make them ready to take actions in time so as to avoid the accidents. According to the statistics from the Ministry of Transportation, 25% of all the traffic accidents are caused by failing to maintain a safe distance or being unable to brake in time when an emergency occurs.. Therefore, how to disseminate the emergency warning messages in an effective way to ensure the vehicular safety is necessary to VANETs.An Emergency Warning Messages (EWM) dissemination scheme for VANETs is proposed in this paper, which takes the drivers' response time into account under the demand of transmitting EWM rapidly and reliably. The scheme includes EWM generating and forwarding mechanisms.The EWM generating mechanism transmitts warning busy tone (WBT) on the dedicated channel to provide the ability for emergency warning which can decrease the probability of vehicular collisions. In order to transmit the EWMs to the rear vehicles in an efficient way so as to reduce the traffic congestion, this paper proposes a EWM forwarding scheme called BRAVE based on rate adaptation. The scheme selects the best bit-rate and the optimal relay nodes to forward the EWM in each hop, therefore, it can reduce the transmitsion time and ensure the efficiency of EWMs broadcasting. BRAVE is mainly used to forward the EWM in a multi-hop way to adjust the traffic to avoid the congestion.Simulations show that the WBT schemes proposed in the paper can transmit the EWM to provide emergency warning and reduce the probability of accidents. When average velocity of vehicles is 60km/h and the density is about 100 vehicles/km, WBT can reduce the probability of collision by 39.7%. The average velocity can be cut down by 18.5% even if vehicles collide, which is expected to alleviate the ponderance of the accident.The BRAVE scheme chooses the optimal bit-rate and the most appropriate intermediate nodes to relay the EWM, which takes 3.9% and 66% less time respectively than the method using the highest bit-rate or the way using the lowest bit-rate to achieve the largest transmission range. The scheme can reduce the forwarding transmission time effectively. Hence, the rear vehicles forwarding to the section can be informed in time to take measures such as braking or changing the road as early as possible so that secondary accidents or congestion can be avoided. The two schemes are able to satisfy the actual requirements of EWM dissemination in ITS, which are the basis of the VANET applications.