Broadcasting Safety Information in Vehicular Networks: Issues and Approaches

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Short summary:

Intelligent transportation systems based on inter-vehicle and vehicle-to-infrastructure communication are expected to improve road safety in the near future. To achieve the future road safety vision, time-sensitive, safety-critical applications in vehicular networks are necessary, and will depend on reliable and efficient broadcast of information with minimum latency.

Due to the high number of nodes on the network, for instance at rush-hours, it is hard to accomplish such requirements. In these conditions, broadcast storms can occur due to message flooding, collisions causing leading to packet loss ratios, and link layer contention. These broadcast storms are related to the nature of routing protocols, because these protocols define the flooding mechanism in the network, and to solve this problem, researchers have proposed several VANET specific protocols.

Location-based methods consist in broadcast packets based on geographic area of sending and receiving vehicles. Some of these protocols solve the broadcast storm problem by reducing the number of broadcast nodes. One approach is to use the vehicles farthest away from the source to perform relaying (MFR). There are also some proposals to use geocast to reduce the range of the broadcast to a smaller region.

Some protocols solve the problem by reducing contention and packet collisions. One alternative is based in reducing the packet loss ratio by dynamically setting the back-off timer for MAC contention widow adjustment, through the information of vehicle location, speed and distance to other nodes. Other protocols reduce contention, through the use of vehicle position and the traffic congestion level to adapt the packet transmission interval, and by integrat...

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...ckets in these networks. The paper also present dedicated short-range

communication

with an enough level of detail, although the review on traffic and mobility patterns is very incomplete. The taxonomy provided is complete. The discussion of each protocol is deep enough in terms of the broadcast storm problem, but the paper do not present other performance arguments to clarify which protocols are more suitable for the broadcast of safety messages. The questions raised regarding some of the protocol assumptions are very pertinent. A more complete conclusions should be provided, since the paper only provides a list of issues related to the problem of broadcasting safety information, and do not compare any of the presented solutions. The paper should provide more information about the trade-offs of each protocol and their performance regarding broadcast messages.

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