| Summary: | 碩士 === 國立臺中教育大學 === 資訊科學系 === 100 === In vehicular ad-hoc networks (VANET), the network topology change rapidly that may cause wireless connection intermittent, due to highly mobility of nodes. But at the same time, the famous wireless technology, such as IEEE 802.11 a, b and g are not suitable for environment of highly mobility. For this reason, the IEEE team modify IEEE 802.11 a, b and g to establish IEEE 802.11p and the IEEE 1609 family of standards for Wireless Access in the Vehicular Environment. The VANETs provides comfortable applications and safety-related applications. Safety-related applications adopts alert message to notify drivers of urgent event on the highway, and allows drivers have more time to react to avoid accident and to protect the safety of drivers and passengers. In safety-related applications, the alert message transmission latency and message redundancy are important issues. The alert message transmission latency of alert message must be in a tolerable range. Otherwise, the probability of car accident may increase extremity. On the other hand, the message redundancy may lead to the broadcast storm problem, which may reduce the reliability of the alert message system.
In this thesis, we focus on the alert message dissemination in VANETs. Generally, the flooding method is adopted to disseminate the alert message on highway. But flooding method may cause the broadcast storm problem. For this reason, we propose Fault-Tolerant Broadcast Protocol, Farthest Node First Protocol and Exponential Back-off Method. The goals of the proposed protocols are to mitigate the broadcast storm problem and reduce the transmission delay of alert message. Finally, we implement the proposed protocol in NS-2 simulator. The simulation results show that our proposed protocol can effectively reduce not only the number of alert messages but also the transmission delay of the alert message and increase the reliability of system.
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