Intervehicle communication (IVC) is an emerging topic in research and application that is getting increasing attention from all major car manufacturers. In this paper, a novel method for scalable information dissemination in highly mobile ad hoc networks is proposed: segment-oriented data abstraction and dissemination (SODAD). With SODAD, information can be distributed in an information range multiple orders of magnitude larger than the transmission range of the air interface, even if only 1%-3% of all vehicles are equipped with an IVC system, e.g., during market introduction. By restricting the method to the dissemination of map/position-based data, scalability is achieved. In the second half of this paper, an example application for the SODAD method is presented: a self-organizing traffic-information system (SOTIS). In SOTIS, a car is equipped with a satellite navigation receiver, an IVC system, and a digital map. Each individual vehicle collects traffic information for its local area. Using the digital map, the traffic information is analyzed based on road segments. By distributing the information in the ad hoc intervehicle network using the SODAD method, a decentralized traffic information system is created. The performance of the proposed methods is evaluated using network simulation with vehicular mobility models. Simulation results for typical scenarios are presented. Furthermore, a prototype implementation based on commercially available standard hardware demonstrates the feasibility of the proposed approach.Index Terms-Car-to-car communication (C2CC), data dissemination, intervehicle communication (IVC), traffic-information system, vehicular network (VANET).

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Conventional Traffic and Travel Information (=I) systems are based on a centralized structure: Sensors deployed at the roadside nwnitor the traffic and transmit the results to a central unit, which performs a situation analysis. P I is made available to the drivers via bmadcast service (e.g. TMC/RDS) or on demand via cellularphone. In contrast to this centralized approach, a decentralized, Self-organizing Trafic Information System (SOTIS) based on Inter-Vehicle Communication ( W C ) has many advantages: It requires no eqensive. infrastructure, can pmvide detailed information for the local area with low delay and is available everywhere. In such an N C based decentralized system, TTI is sensed by each individual vehicle. The information is analyzed, combined with TTI receivedf" other vehicles and the results are distributed using recurring bmadcast packets.In this paper; an adaptive bmadcast scheme for efficient TTI distribution called Provoked Broadcast is presented. The algorithm favors the propagation of signijicant TTI changes within the self-organizing neiwork Nodes adapt their communication behavior to the local envimnment and avoid redundant transmissions. n e performance of the proposed scheme is evaluated by using simulations of iypical trafJic scenarios. Compared to a strictly periodic broadcast, the new scheme decreases the average ermr of information available at an individual vehicle and still requires signifcantly less bandwidth.

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