Kontextbereitstellung in Automobilen Ad-hoc Netzen

Je detaillierter ein Fahrer über den Streckenabschnitt informiert ist, den er in naher Zukunft befahren wird, desto größer ist die Wahrscheinlichkeit, dass er rechtzeitig und angemessen auf komplexe Verkehrssituationen reagiert. Die umfassende Verfügbarkeit von qualitativ hochwertigen Kontextinformationen im Fahrzeug leistet vor diesem Hintergrund einen wichtigen Beitrag zur Erhöhung der Verkehrssicherheit und -effizienz. Ziel dieser Arbeit ist eine zuverlässige Vorhersage der zukünftigen Fahrsituation auf Basis des gemeinschaftlich bekannten Wissens der Verkehrsteilnehmer. Dabei steht die Verwaltung ortsbezogener Kontextinformationen, die Fusion von verschiedenartigen Informationsquellen, sowie die Problematik der Verteilung der von den Fahrzeugen erzeugten Kontextinformationen über automobile Ad-hoc Netzen im Fokus der Arbeit. Aufbauend auf einer formalen Lösungsspezifikation beschreibt die Arbeit einen zweistufigen Bewertungsprozess, der es erlaubt, auf Basis verteilter Sensorbeobachtungen unterschiedlicher Fahrzeuge ein Wahrscheinlichkeitsmaß für das Eintreten eines konkreten Zustands eines relevanten Fahrkontexts abzuleiten. Die räumlichen und zeitlichen Eigenschaften des Kontextaspekts werden dabei gewichtet interpoliert. Anschließend werden auf Basis eines Bayesschen Netzes die kausalen Zusammenhänge unterschiedlicher Kontextaspekte quervalidiert. Zudem wird aufgezeigt, wie Kontextinformationen zwischen Fahrzeugen in einem automobilen Ad-hoc Netzwerk ausgetauscht werden können. Das aus drahtgebundenen Netzen bekannte Konzept der Nutzenmaximierung des Netzwerks wird hierzu auf die speziellen Charakteristika automobiler Netze erweitert. Es wird zudem eine schichtenübergreifende Lösungsarchitektur vorgestellt, die situationsadaptiv sowohl kurze Latenzzeiten für kritische Nachrichten, als auch eine nachhaltige Skalierbarkeit des Netzes in Szenarien mit geringen und hohen Fahrzeugdichten sicherstellt. Der Kanalzugriff und die Verbreitung der Kontextinformationen im Netzwerk basieren dabei auf einer situationsabhängigen Bewertung des Anwendungsnutzens der zu übertragenden Nachrichten. Mit Hilfe von Simulationen wird das Verhalten des Systems bewertet. Durch eine ontologiebasierte Verwaltung wird auch nichtfahrzeugbezogenen Systemen eine domänenübergreifende Nutzung der Sensorinformationen und kausalen Zusammenhänge ermöglicht

Enhancing the security of local danger warnings in VANETs - A simulative analysis of voting schemes

The upcoming deployment of vehicular ad-hoc networks does not only facilitate novel telematics applications, but also poses strong requirements on security. Especially the adoption of active safety applications may raise new threats to road safety if security issues are not properly handled, thus thwarting their initial purpose. In this paper, a special active safety application is considered that enables cooperative foresighted driving through the exchange of local danger warnings, which are based on individual observations and refer to the current road condition. From a security point of view, the decision whether or not such an application should rely on a reported hazard, is a crucial issue, which cannot be completely protected by conventional security measures. We propose an additional security mechanism based on an information centric evaluation of the plausibility of received hazard messages. We developed four decision methods, which are based on voting schemes, and evaluated them by simulation using two attacks trying to manipulate the decision process by distributing false information. Our results indicate that the proposed information centric evaluation of remote observations is a reasonable means to increase the stability and security of a cooperative local danger warning service.

RESULTS FROM THE WILLWARN PROJECT

In the PReVENT sub-project WILLWARN a decentralized hazard warning application based on vehicle-to-vehicle communication was developed and demonstrated. One or more vehicles detect a potential hazard and communicate this information. The hazard information is distributed in a decentralized information network. The system in a receiving vehicle approaching the hazardous location warns the driver. This paper presents the results regarding system design, information coding, data processing in a decentralized information network, and communication aspects. The in-depth work revealed several fundamentally new aspects of decentralized information systems. This paper emphasizes on aspects regarding the standardization of vehicle-to-vehicle communication systems

Strategies for context-adaptive message dissemination in vehicular ad hoc networks

Abstract — In future deployments of Vehicular Ad hoc Networks (VANETs) safety-related applications such as local danger warning (LDW) will use broadcast-based communication schemes to transmit information to other vehicles within the network. The unlimited flooding of a message throughout the whole network however, is neither feasible nor intended. The high resulting traffic load would congest the shared wireless medium and prevent other, potentially highly relevant and time-critical messages from getting access to the medium. Existing strategies to limit redundant packet retransmissions manage to make broadcast-based data packet dissemination more efficient and reliable. However, they do not take into account the individual network’s nodes interest in information. In fact, the static mechanisms proposed are not adequate to leverage the limited network resources as efficiently as possible in varying network conditions and to transport information to where it is needed as fast as possible. Therefore, we propose an altruistic communication scheme which differentiates data traffic according to the benefit it is likely to provide to potential recipients. A system for calculating and leveraging message benefit and two different node architectures are presented. With the help of a comprehensive simulation environment, the performance of our concept is analyzed. Comparative simulative studies show that an improvement of the benefit provided to all the participants in a VANET is also possible with the help of the readily available IEEE 802.11e standard, but to a lower extent. I

A Framework for Network Utility Maximization in VANETs

A Framework for Network Utility Maximization in VANETs Vehicular Ad hoc Networks (VANETs) are expected to have great potential to improve both traffic safety and comfort in the future. Safety and traffic related applications will typically use broadcast-based communication schemes to disseminate messages within the network. Existing strategies to reduce redundant retransmissions and to improve reliability and efficiency of message dissemination rely on inflexible transmission limitations.They are not adequate to efficiently deal with the limited network resources efficiently both in sparse and in dense networks. Apart from that, they do not take into account the individual network nodes ’ interest in information. The goal of our concept is to provide network participants with data that has the highest utility for them with a latency as small as possible, independent of the actual network load. Our concept envisages the context-adaptive differentiation of data traffic according to current information relevance to allow for an optimal utilization of the limited network resources. In this paper, we propose methodologies for quantifying message relevance, present different mechanisms for realizing data prioritization and compare our solution with the IEEE 802.11e approach. 1