| Abstract |
In this thesis, we study how the vehicles that witness or sense the accidents can quickly disseminate emergency messages in a vehicular ad hoc network (VANET). The current international medium access control (MAC) standard for VANETs is IEEE 802.11p, which did not address this issue. The simplest way to disseminate emergency messages is flooding, which easily induces the broadcast storm problem, thus severely wasting bandwidth. An alternative way is to maintain clusters in a VANET. Then when an accident occurs, the cluster head near to that place can ask its farthest member to relay the emergency message. However, such an approach requires high overhead to constantly maintain cluster structure, while accidents rarely occur. Therefore, we design a new emergency message anycast protocol, named TSDA, in which the witness vehicle can quickly disseminate emergency messages by estimating the number of its neighbors even all vehicles do not broadcast beacons. More importantly, TSDA can coexist with 802.11p. Simulation results show that TSDA outperforms the existing 3P3B protocol in terms of average one-hop delay, average message progress, and message dissemination speed. |
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