ne of the major goals of vehicular ad hoc networks (VANETs) is to support traffic safety. Cooperative awareness applications require frequent and low-delay information exchange among vehicles, including data such as current position, movement, and acceleration. This is realized by broadcasting socalled (single-hop) beacon messages. As a result, every vehicle is aware of other vehicles within a certain range. Beaconing is also the basic supporting process that enables geographic routing and message dissemination. However, this also requires a significant amount of bandwidth. The higher the frequency and thus the accuracy, the higher the bandwidth consumption. The first phase of research on VANETs has set the boundary conditions in terms of basic communication protocols and routing paradigms. Communication in VANETs will be based on IEEE 802.11p. Message dissemination and routing are based on geocast principles. Beaconing takes place on a single communication channel (commonly referred to as the control channel) that is shared by all nodes. However, it has also been shown in [1] that the limited bandwidth of the wireless channel has a severe impact on the efficiency of the communication. This means that if the beacon rate is fixed, channel load may increase too much in scenarios with high vehicle density. High channel utilization increases the information loss as packets are received erroneously, which is especially observed at large distances between sender and receiver. Simply reducing the beacon rate is not a suitable solution because it reduces the information quality at the same time. The error between the real position of a vehicle and the last known position retrieved from a beacon increases as the beacon rate is reduced. This results in position inaccuracies, which may disturb correct operation of active safety applications, which rely on accurate and up-to-date information. Currently, there is no final recommendation for a particular static beacon rate. No upper boundary in terms of maximum channel load has been specified. Furthermore, no requirements from the different applications have yet been clearly defined. As a consequence, even minimum and maximum beacon rate are hard to derive as these two boundaries have to satisfy all imaginable road traffic situations. In this article we pave the way for further enhancements of beaconing algorithms for the second phase of research on VANETs. After a short assessment of the current state of the art, we present a detailed analysis of the problem space and how different beacon rates influence 1) the offered load to the channel and 2) the resulting average and maximum accuracy of information Based on this problem evaluation, we motivate a flexible approach to control both appropriately. For this purpose, we propose a situation adaptive beaconing process that adapts the beacon rate continuously. The design space and different candidates for such an algorithm are introduced in this article.  In the future intervehicle communication will make driving safer, easier, and more comfortable. As a cornerstone of the system, vehicles need to be aware of other vehicles in the vicinity. This cooperative awareness is achieved by beaconing, the exchange of periodic single-hop broadcast messages that include data on the status of a vehicle. While the concept of beaconing has been developed in the first phase of research on VANETs, recent studies have revealed limitations with respect to network performance. Obviously, the frequency of beacon messages directly translates into accuracy of cooperative awareness and thus traffic safety. There is an indisputable trade-off between required bandwidth and achieved accuracy. In this work we analyze this trade-off from different perspectives considering the consequences for safety applications. As a solution to the problem of overloading the channel, we propose to control the offered load by adjusting the beacon frequency dynamically to the current traffic situation while maintaining appropriate accuracy. To find an optimal adaptation, we elaborate on several options that arise when determining the beacon frequency. As a result, we propose situation-adaptive beaconing. It depends on the vehicle's own movement and the movement of surrounding vehicles, macroscopic aspects like the current vehicle density, or microscopic aspects.
The study in REF analyzes the effects of adapting the beacon rate with respect to reduced accuracy and changing the offered load.
Exploration of adaptive beaconing for efficient intervehicle safety communication
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IEEE Network
Computer Science