Andre Ebner

Information dissemination in self-organizing intervehicle networks

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.

SOTIS - a self-organizing traffic information system

Traffic and travel information (TTI) systems in use today are based on a centralized structure. Sensors along the roadside monitor traffic density and transmit the results to a central unit where a situation analysis of the global traffic scenario is performed. The resulting traffic information is made available to drivers via broadcast service or alternatively on demand via cellular phone. Within the FleetNet project, a completely different proposal to establish a powerful traffic information system is developed and analyzed, which is based in inter-vehicle communications (IVC). All vehicles are part of a self-organizing traffic information system (SOTIS): each vehicle monitors the locally observed traffic situation by recurrently receiving data packets with detailed information from other vehicles. A traffic situation analysis if performed in each individual vehicle and the result is transferred via wireless data-link to all surrounding vehicles in the local neighborhood. No sensors along the highways, no central units and no local broadcast stations or cellular networks are needed, which minimizes infrastructure costs. The complete system can be easily avoided completely. Simulation results demonstrate that the proposed SOTIS technique can easily provide detailed information for each vehicle with an individual information range of more than 50 km from the current position with high accuracy and low delay. Even in situations where only a small fraction of all vehicles (e.g. 2%) is equipped with the SOTIS technology, the full functionality of a traffic information system is available.

Position-aware ad hoc wireless networks for inter-vehicle communications: the Fleetnet project

The Fleetnet project aims at the development of a wireless ad hoc network for inter-vehicle communications. We present the rationale behind the choice of an appropriate radio hardware and the use of a position-based routing approach and outline applications to exploit the Fleetnet platform. In addition, we discuss simulation of vehicle movements as a basis for protocol evaluation as well as aspects of Internet integration of Fleetnet. We state the basic problems together with the intended approach of tackling these challenges, thereby providing an overview of the Fleetnet project

Adaptive broadcast for travel and traffic information distribution based on inter-vehicle communication

Conventional Traffic and Travel Information (TTI) systems are based on a centralized structure: Sensors deployed at the roadside monitor the traffic and transmit the results to a central unit, which performs a situation analysis. TTI is made available to the drivers via broadcast service (e.g. TMC/RDS) or on demand via cellular phone. In contrast to this centralized approach. a decentralized, Self-Organizing Traffic Information System (SOTIS) based on Inter-Vehicle Communication (IVC) has many advantages: It requires no expensive infrastructure. can provide detailed information for the local area with low delay and is available everywhere. In such an IVC based decentralized system, TTI is sensed by each individual vehicle. The information is analyzed, combined with TTI received from other vehicles and the results are distributed using recurring broadcast packets. In this paper; an adaptive broadcast scheme for efficient TTI distribution called Provoked Broadcast is presented. The algorithm favors the propagation of significant TTI changes within the self-organizing network. Nodes adapt their communication behavior to the local environment and avoid redundant transmissions. The performance of the proposed scheme is evaluated by using simulations of typical traffic scenarios. Compared to a strictly periodic broadcast, the new scheme decreases the average error of information available at an individual vehicle and still requires significantly less bandwidth.

Decentralized slot synchronization in highly dynamic ad hoc networks

Ad hoc networks provide data communication services without being bound to an existing infrastructure. An exciting application of highly dynamic ad hoc networks is the exchange of data between running vehicles. For air-interfaces based on a slotted time division multiple access (TDMA) scheme, slot synchronization is required among the rapidly moving vehicles. A scheme for completely decentralized slot synchronization of nodes in an inter-vehicle communication (IVC) environment is presented. To evaluate the performance of the proposed mechanism, the influence of real synchronization to the network throughput in case of a slotted ALOHA medium access protocol is investigated. Simulation results indicate only a minor throughput degradation compared to an ideal slot synchronization.

Synchronization in ad hoc networks based on UTRA TDD

Within the FleetNet project an ad hoc radio network for intervehicle communications (IVC) and road telematics is being developed. For the air interface, the framework of the UMTS Terrestrial Radio Access time division duplex (UTRA TDD) standard has been selected as the most promising candidate. The requirements and challenges for synchronization in an ad hoc network with rapidly changing topology and high velocities are discussed. Solutions for synchronization in ad hoc networks based on UTRA TDD are proposed and evaluated by means of link-level simulations. The results indicate promising performance with only minor changes to the UTRA TDD standard specifications.

Performance of UTRA TDD ad hoc and IEEE 802.11b in vehicular environments

The FleetNet project aims at the development of a wireless ad hoc network for inter-vehicle communications (IVC). As a basis for the air-interface, the framework of the UMTS terrestrial radio access time division duplex (UTRA TDD) has been selected as the most promising candidate. Since UTRA TDD was developed for operation in a cellular network structure, modifications are required to enable mobile nodes to communicate in ad hoc mode without the existence of base stations. In particular, this comprises changes to physical (PHY) layer, medium access control (MAC) and radio resource management (RRM). The focus of this paper is the PHY layer of the air-interface and the resulting challenges in highly dynamic vehicular environments. The performance of the UTRA TDD ad hoc mode is assessed and compared to the IEEE 802.11b standard using link-level simulations. Results indicate that the UTRA TDD ad hoc PHY outperforms IEEE 802.11b in a typical highway scenario with very large relative velocities. In urban traffic environments with strong multipath propagation, IEEE 802.11b is not able to meet the required performance in terms of packet losses.

10 Years of Car-2-X Communication – a Success Story?

Abstract For more than ten years, car-2-x communication has been a major topic of research in the scientific community and an important development focus for the automotive industry. First, this article takes a retrospective look at the evolution of car-2-x and the two different communication paradigms: decentralized car-2-car communication and centralized cellular solutions. Afterwards, a comparison of their technical advantages and limitations is presented, respectively. The result shows that in order to implement safety-relevant applications, car-2-car communication has strong advantages compared to cellular technologies but requires high market penetration. However, its introduction solely for safety applications is difficult since the required penetration will not be achieved until several years after initial deployment. Therefore, car-2-car communication must provide a benefit to the customer, even in the phase of market introduction. For this purpose, the article outlines an approach called SODAD (Segment-Oriented Data Abstraction and Dissemination). It offers a possibility to introduce decentralized vehicular applications with early customer benefit, in order to enable safety applications based on car-2-car communication on a long term.

An air-interface for ad hoc networks supporting high mobility

In this paper, a novel air-interface is presented for FleetNet1, a self-organizing network for inter-vehicle and vehicle-to-roadside communication. The air-interface is based upon the low-chip-rate version of UMTS/TDD. To adapt the cellular UMTS standard to an air-interface for ad hoc networks, changes of the physical layer, medium access control sub-layer and radio resource management are required. An overview of the required modifications is given here. Particularly, a decentralized synchronization mechanism is presented and analyzed by means of simulations. Furthermore, changes for the medium access control are explained in detail, which allow for an efficient operation in partly meshed networks and prioritization. Performance results of the overall system considering throughput and delay are derived by means of analytical evaluations and event-driven simulations. Based on realistic mobility models, it is shown that the presented solution provides a robust communication platform even in vehicular environments. The proposed air-interface is a cost-effective solution not only for inter-vehicle communication, but also for ad hoc networking in general, benefiting from the mass-market of UMTS.

FleetNet – Anwendungen für mobile Ad-hoc-Netzwerke

ZUSAMMENFASSUNG Das Forschungsprojekt FleetNet zielt auf den Einsatz von mobilen Ad-hoc-Netzen für die Fahrzeug-Fahrzeug-Kommunikation. Anwendungsgebiete sind sicherheitsrelevante Fahrerassistenzsysteme, dezentrale Floating-Car-Data-Anwendungen sowie Kommunikations- und Internetdienste. Die Auswahl einer Funkhardware, die Entwicklung von geeigneten Kommunikationsprotokollen sowie die prototypische Demonstration der entwickelten Lösungen sind die Hauptziele. Wesentlich zu lösende Problemstellungen umfassen die Entwicklung von positionsbasierten Routingalgorithmen, das Kanalzugriffsproblem, die Bestimmung und Anpassung einer geeigneten Funkhardware und die Kommunikation ins Internet über stationäre FleetNet-Stationen. In diesem Beitrag werden Anwendungen vorgestellt, die mit einer Flotte von Experimentierfahrzeugen im praktischen Einsatz erprobt werden.