Showing papers by "Hannes Hartenstein published in 2007"

Overhaul of ieee 802.11 modeling and simulation in ns-2

Abstract: NS-2, with its IEEE 802.11 support, is a widely utilized simulation tool for wireless communications researchers. However, the current NS-2 distribution code has some significant shortcomings both in the overall architecture and the modeling details of the IEEE 802.11 MAC and PHY modules. This paper presents a completely revised architecture and design for these two modules. The resulting PHY is a full featured generic module able to support any single channel frame-based communications (i.e. it is also able to support non-IEEE 802.11 based MAC). The key features include cumulative SINR computation, preamble and PLCP header processing and capture, and frame body capture. The MAC accurately models the basic IEEE 802.11 CSMA/CA mechanism, as required for credible simulation studies. The newly designed MAC models transmission and reception coordination, backoff management and channel state monitoring in a structured and modular manner. In turn, the contributions of this paper make extending the MAC for protocol researches much easier and provide for a significantly higher level of simulation accuracy.

Enabling efficient and accurate large-scale simulations of VANETs for vehicular traffic management

Abstract: To study the impact of inter-vehicle communications on (vehicular) transport efficiency, e.g., for traffic management purposes, there is a need for efficient and accurate large-scale simulations that jointly consider both, the vehicular traffic and the communication system. To overcome the scalability limitations of current discrete event-based network simulators like NS-2, we propose a hybrid simulation approach that can significantly reduce the number of scheduled events by making use of statistical models. Basically, we treat some data traffic, which is not the primary concern of the simulation study, as 'noise' (e.g., beaconing of nodes). While accurately modeling this background traffic we only need to simulate via discrete event-based simulation the actual application we are interested in (e.g., a data dissemination protocol). We outline how the characterization of the background traffic is gained, statistically validated and used. The achievable speed-up is demonstrated in a first application study where a speed funnel is built using inter-vehicle communications. In this scenario, the conservatively estimated speed-up factor is about 500 compared to a pure discrete event-based simulation.

Simulation platform for inter-vehicle communications and analysis of periodic information exchange

Abstract: Due to the large amount of nodes that could comprise a vehicular network, simulation is a valuable tool used for the design and analysis of inter-vehicle communication protocols. In this paper we first describe all the components of a simulation framework that has ns-2 as core building block. Our main contributions are an accurate implementation of the MAC and PHY modules adjusted to vehicular environments together with a well defined set of metrics to evaluate communication protocols for vehicular networks. Second, we make use of the simulation framework to perform a detailed analysis of periodic exchange of broadcast messages when adjusting transmission power and packet generation rate for different propagation models

Method for information dissemination in a communication network

Abstract: A method for information dissemination in a communication network, preferably in a vehicular ad hoc network (VANET), wherein the communication network (1) comprises a multitude of communication nodes (N) which are aware of their geographical position, and wherein the dissemination process is initiated by one of the nodes - originator node (O) - by sending a unicast message that includes the information to be disseminated to a specific node - first forwarder node (F1) - within a relevant area (RA) in which the information is to be disseminated, is characterized in that other nodes (C1 , C2, C3) in the relevant area (RA), which receive the message sent by the originator node (O) to the first forwarder node (F1), elect a forwarder node, respectively, and perform a unicast retransmission of the message to the elected forwarder node on the basis of a timer-based contention process.

Vehicular Ad Hoc Networks: How to Show the Impact on Traffic Safety?

Abstract: Vehicular ad hoc networks, in which vehicles directly exchange information through wireless communication, promise to increase transport efficiency and traffic safety. In this paper we address the challenge of demonstrating the beneficial impact of vehicular ad hoc networks on traffic safety via simulation. We provide a blueprint for such a simulation experiment. The required building blocks discussed in this paper comprise accident modeling, safety metrics, design of an accident prevention application (APA) based on vehicular networks, and a model of the performance of the communication system. We then focus on the aspect of how an APA can be designed and formalized with the help of Markov reward processes, and show that the model is mathematically 'well-behaving'. The APA will allow us in the future to assess a communication system's performance with respect to traffic safety.

Föderatives und dienstorientiertes Identitätsmanagement: Konzept und Erfahrungen

Abstract: ZUSAMMENFASSUNG Dieser Artikel beschreibt die Architektur eines integrierten Identitätsmanagements an einer Universität. Der beschriebene Ansatz basiert auf der Sicht der Universität als Föderation organisatorischer Einheiten und auf dem Prinzip der Dienstorientierung. Die Datenhaltung von Identitätsinformation erfolgt dezentral, wobei lediglich Abbildungsinformation, die für das “in Beziehung setzen” von Identitätsinformation zwischen den organisatorischen Einheiten notwendig ist, zentral vorgehalten wird, wenn dies vom Nutzer gewünscht wird. Der Aufbau eines solchen Systems und die technische Realisierung, welche klassische Identitätsmanagementkomponenten mit einem modernen, auf Web Services basierenden Ansatz vereint, werden anhand der Umsetzung an der Universität Karlsruhe beschrieben.