Design And Analysis Of Multihop Broadcast Algorithms In Vanet

With the development of Intelligent Transportation System, Vehicle Ad-Hoc Network (VANET) has drawn increasing attention from both academia and industry. Nowadays, more and more applications developed for VANET utilize the method of multihop broadcast as a transmission approach to either explore nearby neighbor nodes or deliver critical safety messages within a target geographical area. However, traditional flooding algorithm may result in so-called "broadcast storm" problem, a scenario in which there is a great number of contention and collision because of excessive broadcast data packets. And the serious problem would lead to dramatical deterioration of the network performance.In order to obtain efficient and reliable message broadcast transmission performance in real vehicular environment, this paper proposes a novel Double-timer based broadcast algorithm (DT-BA), which can mitigate the amount of redundancies and also reduce the data transmission delay.In proposed DT-BA, a new relay selection scheme is designed. The sum value of two timers is utilized to decide whether the node forwards the received new packet. The first timer is used to stabilize the receiving process, and before it expires, the node would update the relative distance to the last sender of the packet according to some rule. When the first timer is due, the second timer would be initiated, the value of which is calculated based on the relative distance from the node to the last one-hop sender. The relay selection scheme used in the DT-BA can ensure that only the furthest receiver from the last sender of the packet would forward the packet, not only can effectively reduce the number of relays in the network but also decrease the data packet transmission delay. Meanwhile, since it is very common that several types of message with different safety level exist in VANET, DT-BA introduces a priority queue mechanism to guarantee that emergency message can get the prior and fast delivery. In addition, a timeout retransmission strategy is implemented to increase the reliability of the communication network and make as more as possible nodes in the target area can receive the data packet.Simulation results under NS2environment reveal that proposed DT-BA provides the fastest packet penetration speed, the lowest ratio of forwarders to total nodes and the least average transmission delay of the packet compared with the algorithm of Slotted1-persistence and the traditional flooding based one, and also it can guarantee the reliable and efficient propagation of both emergency and normal messages.