Over the past several years, there has been significant interest and progress in using wireless communication technologies for vehicular environments in order to increase traffic safety and efficiency. Due to the fact that; these systems are still under development and large-scale tests based on real hardware are difficult to manage, simulations are a widely-used and cost-efficient method to explore such scenarios. Furthermore, simulations provide a possibility to look at specific aspects individually and to identify major influencing effects out of a wide range of configurations. In this context, we use the HP XC4000 for an extensive and detailed sensitivity analysis in order to evaluate the robustness and performance of communication protocols as well as to capture the complex characteristics of such systems in terms of an empirical model.

“Smart” vehicles of the future are envisioned to aid their drivers in reducing fuel consumption and emissions by wirelessly receiving phase-shifting information of the traffic lights in their vicinity and computing an optimized speed in order to avoid braking and acceleration maneuvers. Previous studies have demonstrated the potential environmental benefit in small-scale simulation scenarios. To assess the overall benefit, large-scale simulations are required. In order to ensure computational feasibility, the applied simulation models need to be simplified as far as possible without sacrificing credibility. Therefore this work presents the results of a sensitivity analysis and identifies gear choice and the distance from the traffic light at which vehicles are informed as key influencing factors. Our results indicate that a suboptimal gear choice can void the benefits of the speed adaptation. Furthermore, we present first results of a scale-up simulation using a real-world inner-city road network and discuss the range in which we expect the saving in fuel consumption to be in reality.

PRE-DRIVE C2X is a project funded within the 7th Framework Programme of the EU to support the development and introduction of cooperative systems. One major part of this work is the creation of a comprehensive tool set of simulation models integrating all fields of expertise involved. The objective is to create, test and apply an integrated simulation tool set that allows to simulate and evaluate the interaction between vehicle traffic, vehicular communication and co-operative applications. Each of these three areas is treated by dedicated models. Additionally the environmental effects are modelled by a separate modelling approach with detailed algorithms for vehicle dynamics and engine behaviour. The process to arrive at such a model combination from user requirements over pre-existing know-how and other significant steps are described as well as the current status of the work.

In this paper we propose a simulation-as-a-service approach to evaluate ITS applications. We segment a simulation process in two building blocks: a web-interface/server front-end used by users to configure the remote simulations of their ITS application, and a back-end consisting of a controller and a HCC platform to conduct the remote simulations. The controller is in charge of configuring the HCC platform as well as distributing and scheduling the simulations on it. HCC platforms usually provide users with only a restricted control on the simulation environment and a limited set of available libraries. To mitigate these drawbacks, we make use of the virtualization support of recent HCC platforms and employ Kernel-based Virtual Machines.

This chapter contains sections titled: Introduction: Challenges and Requirements A Survey on Proposed MAC Approaches for VANETs Communication Based on IEEE 802.11p Performance Evaluation and Modeling Aspects of Congestion Control Open Issues and Outlook References

Today's advanced simulators facilitate thorough studies on VANETs but are hampered by the computational effort required to consider all of the important influencing factors. In particular, large-scale simulations involving thousands of communicating vehicles cannot be served in reasonable simulation times with typical network simulation frameworks. A solution to this challenge might be found in hybrid simulations that encapsulate parts of a discrete-event simulation in an analytical model while maintaining the simulation's credibility. In this paper, we introduce a hybrid simulation model that analytically represents the probability of packet reception in an IEEE 802.11p network based on four inputs: the distance between sender and receiver, transmission power, transmission rate, and vehicular traffic density. We also describe the process of building our model which utilizes a large set of simulation traces and is based on general linear least squares approximation techniques. The model is then validated via the comparison of simulation results with the model output. In addition, we present a transmission power control problem in order to show the model's suitability for solving parameter optimization problems, which are of fundamental importance to VANETs.

Vehicular ad hoc networks are conceived as a means to increase traffic safety. Primary means to demonstrate their beneficial impact before deployment are computer simulations that comprise communication models, mobility models of vehicles and models of VANET applications. In particular, the movement behavior of vehicles poses questions when evaluating traffic safety since driver models typically do not allow accidents to happen. In this paper we address modifications to the popular Wiedemann model and present an integration of the modified driving behavior to the traffic simulator VISSIM which thus enables simulations containing accidents. Finally, we show in a simulative study how locally available information on the current traffic situation can contribute to safer road traffic. Our contributions represent a first step on how to assess VANETs with respect to traffic safety.

Summary A robust exchange of messages between vehicles via radio communication represents a key problem of vehicular ad hoc network (VANET) research. Environmental influences and the multitude of communicating nodes result in challenging communication conditions that have to be taken into account when assessing the potential benefit of VANETs for traffic safety and efficiency applications. In this paper we discuss an appropriate modeling of three influencing factors on the communication behavior to establish a basis for credible simulation results. In detail, we analyze the effects of fast-fading, capturing, and cumulative noise on vehicular communications and illustrate their considerable influence on a simulation's outcome. As a second contribution, we provide an empirical model for the probability of packet reception that is based on the proposed simulation methodology. The model thus allows to determine credible simulation results without being dependent on the complexity of detailed simulations. The saved computational effort facilitates the assessment of VANETs in large-scale scenarios and the consideration of communication specifics in the design process.

The control of vehicles' radio communication behavior to deal with the constrained available wireless bandwidth has been identified as a key challenge in VANETs. As an element of congestion control, this paper addresses distributed transmission power control as a means to control the impact of periodic transmissions ('beacons') on the overall channel load. By also considering recently discussed fairness issues, we first examine the trade-off between the effectiveness of controlling the channel load on the one hand and the corresponding costs in terms of the required packet overhead on the other hand. We provide insights to the underlying estimation problems and present a sensitivity analysis with respect to non-homogeneous vehicular traffic densities and non-perfect channel conditions. Second. based on the analysis, we propose a segment-based power adjustment approach based on a distributed vehicle density estimation. The approach put. forward in this paper reduces overhead by two orders of magnitude compared to previous approaches while still being effective in controlling the channel load.

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.

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.

Inter-vehicle communication has to be able to cope with adverse conditions like received signal strength fluctuations, channel load saturation, or high mobility to provide robust communication services as a basis for safety-related applications. We show the impact of realistic radio models on the performance of vehicular ad hoc networks. While most of the implications are known, some of them appear to be underestimated in vehicular scenarios. We want to convince protocol designers of `thinking in probabilities' when intending to achieve reliable communications. Among the contributions of this paper are a discussion of link layer desynchronization, a derivation of probabilities of bidirectional links and associated costs, and a fairness concept.

Security is a precondition for the success of an electronic market system. Unless the system is able to provide some mechanism to ensure authentication, authorization, and secure data transmission, the system will have problems to be accepted by both customers and providers. In this paper, we will discuss some ideas how to add security to a distributed electronic market system that is designed platform-independently on the base of web services. We will show how we have implemented these ideas in a system for an electronic market for scientific literature.