Abstract
Vehicular ad hoc networks have been developed in consideration of advancing driving safety. In driving-safety applications, rapid dissemination of warning messages is highly demanded to avoid accidents involving incoming vehicles. Broadcast transmission is considered the most appropriate technique to spread warning messages because it can simultaneously reach all neighboring nodes within a transmission range using only a brief wireless media access. However, blindly broadcasting redundant messages may severely overcrowd wireless media channels and provoke transmission collisions; this is known as the broadcast storm problem. In order to reduce broadcast redundancy, broadcasting must be intelligently controlled. Simultaneously, an intelligent broadcast scheme should aim to reduce the number of hops needed to arrive at a destination, to achieve smaller propagation delay. In this paper, we observed the behavior of a few broadcast schemes and found that their performances can be explained as limiting a space to control the number of contentions in broadcasting. From the observation, we propose a limited area-based (LAB) scheme to achieve a shorter propagation time as well as a smaller number of redundant broadcast messages. The proposed scheme can maintain a proper collision rate to obtain a faster propagation time by adjusting the size of an area in which broadcasting nodes belong. Performance evaluation results from simulation show that the proposed scheme is feasible and reasonable.
Highlights
Vehicular ad hoc networks (VANETs) are developed as a component of intelligent transportation systems (ITS) technology to increase driving safety [1]
Because the area limited by LAB50 is larger than limited area broadcast (LAB)-25, the degree of contention will be higher in higher density and the collisions will be more frequent than LAB-25, which leads to a longer propagation delay than LAB-25
In this work, we observed that even simple broadcast can be used to deliver emergency messages in a practical view7 if it has a contention windows (CWs) large enough to handle a high degree of contentions
Summary
Vehicular ad hoc networks (VANETs) are developed as a component of intelligent transportation systems (ITS) technology to increase driving safety [1]. To reduce the redundant messages, distancebased broadcast schemes [11–13] select the furthest node as a relay node to minimize the number of hops and to decrease collision rates by controlling the size of the contention window based on distance. To minimize the number of hops, and achieve an expected decrease in propagation delay, [11–13] developed distance-based broadcast schemes considered the distance between senders and receivers They assign higher rebroadcasting privileges to nodes located close to the border of the transmission range. If the sender cannot receive the rebroadcast message within a certain time, it means none of the nodes is selected as a relay node In this case, radius r will be doubled as a sort of congestion control technique, similar to that of IEEE 802.11 contention window or that of TCP; the distance from S(xs, ys) to P(x, y) will be decrease as much as r increases. The CW of 32 achieves a low rate (= about 63 %) at a density of 100, which means the size of the CW is not sufficient to resolve the degree of contention at a density of 100
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