David Eckhoff

A computationally inexpensive empirical model of IEEE 802.11p radio shadowing in urban environments

We present a realistic, yet computationally inexpensive simulation model for IEEE 802.11p radio shadowing in urban environments. Based on real world measurements using IEEE 802.11p/DSRC devices, we estimated the effect that buildings and other obstacles have on the radio communication between vehicles. Especially for evaluating safety applications in the field of Vehicular Ad Hoc Networks (VANETs), stochastic models are not sufficient for evaluating the radio communication in simulation. Motivated by similar work on WiFi measurements, we therefore created an empirical model for modeling buildings and their properties to accurately simulate the signal propagation. We validated our model using real world measurements in a city scenario for different types of obstacles. Our simulation results show a very high accuracy when compared with the measurement results, while only requiring a marginal overhead in terms of computational complexity.

IVC in Cities: Signal Attenuation by Buildings and How Parked Cars Can Improve the Situation

We study the effectiveness of Inter-Vehicle Communication (IVC) in urban and suburban environments at low node densities, with a particular focus on cooperative awareness and traffic safety. The recently standardized DSRC/WAVE protocol suite defines a platform for such applications, which mainly focus on beaconing, i.e., periodic 1-hop-broadcast. In general, such safety relevant transmissions are defined by time criticality. One of the major problems to be solved is how to tackle the very difficult and complex radio signal attenuation due to buildings and other obstacles, especially in cities. Typical concepts address this problem by requiring all vehicles to also act as relays or by using dedicated Roadside Units (RSUs). We show how such systems may be operated more efficiently and how the situation can be further improved by relying on parked vehicles in addition to, or as a replacement for, RSUs. Given the fact that the U.S. DOT is already evaluating whether to make DSRC mandatory for new cars, wide availability of radio equipped cars can be predicted; also the impact in terms of energy consumption is negligible. We performed an extensive set of simulations to evaluate the negative impact of buildings at low node densities and the benefit of our proposal. Our results clearly indicate that situation awareness can be significantly improved. When disseminating safety critical events in a realistic scenario, reasonable numbers of parked cars can increase cooperative awareness by up to 25%, a factor which requires an unreasonably costly number of RSUs. To the best of our knowledge, we are the first to propose the utilization of parked vehicles as relay nodes for safety applications in vehicular networks.

Driving for Big Data? Privacy Concerns in Vehicular Networking

Communicating vehicles will change road traffic as we know it. With current versions of European and US standards in mind, the authors discuss privacy and traffic surveillance issues in vehicular network technology and outline research directions that could address these issues.

On the Necessity of Accurate IEEE 802.11P Models for IVC Protocol Simulation

In the scientific community, Inter-Vehicle Communication (IVC) protocols are frequently evaluated using simulation techniques, often using variants of WiFi stacks instead of IEEE 802.11p, which constitutes the basis for the new DSRC/WAVE standard. We discuss the necessity of using accurate WAVE models based on an extensive set of simulation experiments using: an IEEE 802.11b model, an IEEE 802.11b model tweaked to work in the same frequency range and using similar timings like IEEE 802.11p, as well as a fully featured channel hopping WAVE model. Even though, intuitively, the use of the different protocols will lead to a different network behavior, to the best of our knowledge, there has been no qualitative and quantitative evaluation or comparison of both worlds. According to our results, we can conclude that the simple WiFi model may indeed be used, but only for extremely sparse scenarios - this is exactly what has been validated using field tests. In denser traffic scenarios there is a significant deviation of the protocol behavior between WiFi (and its adapted variant) compared to WAVE. Thus, especially in dense scenarios, the application behavior is strongly influenced if simulated with the wrong model - leading to unrealistic results.

A performance study of cooperative awareness in ETSI ITS G5 and IEEE WAVE

The idea of wirelessly connected vehicles has long ceased to be a vision as researchers from both academic and industrial institutions and field operational tests all over the world are contributing to bringing this technology to life. Both ETSI and IEEE have been working on respective standards (ETSI ITS G5 in Europe, IEEE WAVE in North America) to enable this new application of wireless communication. In this paper we compare medium access in these systems by means of an extensive simulation study while focusing on the transmission of periodic safety messages on the control channel. We observe that for different reasons high node density scenarios appear to be critical for the overall performance of both systems. This includes end-to-end delay, packet error rates and a non-optimal channel utilization that leaves room for improvement. We find that the approach proposed by ETSI ITS G5 with Decentralized Congestion Control (DCC) may access the channel rather conservatively but still outperforms IEEE WAVE in most of the scenarios.

Cooperative Awareness at Low Vehicle Densities: How Parked Cars Can Help See through Buildings

Many safety applications in Intelligent Transportation Systems (ITS) require vehicles to be aware of the presence of nearby cars, but - especially in urban and suburban regions - buildings and other obstacles may block radio transmissions. In the literature, multi-hop relaying by neighboring cars has been demonstrated to perform well at disseminating safety broadcasts in the presence of obstacles. At night, in areas with low traffic density, or when the penetration rate of Car-2-X devices is low, however, there are likely to be too few relaying cars available. This again leads to the problem that vehicles which are not in line-of-sight frequently cannot be sensed either. To the best of our knowledge, we are the first to help overcome this problem by utilizing parked cars as relay nodes. We study the effectiveness and the necessity of this approach with the help of extensive simulative studies and real life experiments. We show how, for scenarios with few equipped cars, the utilization of parked cars proves crucial to support safety applications. When disseminating safety critical events in a realistic scenario, parked cars can increase cooperative awareness by over 40% in total.

Potentials and limitations of Green Light Optimal Speed Advisory systems

The reduction of CO2 emissions is one of the most anticipated features of future transportation systems. Smart traffic lights are believed to contribute to achieving this by either adapting their signal program or by informing approaching drivers. In this paper we investigate the potentials and limitations of the latter, that is, Green Light Optimal Speed Advisory (GLOSA) systems in a realistic, large scale simulation study. We examine the impact of different equipment rates of both traffic lights and vehicles on environmental related metrics but also study how these systems can increase the comfort for drivers by reducing waiting times and the number of stops. We find that at low traffic densities these systems can meet all their goals and lower CO2 emissions by up to 11.5% whereas in dense traffic several side-effects could be observed, including overall longer waiting times and even higher CO2 emissions for unequipped vehicles.

Toward Realistic Simulation of Intervehicle Communication

The quality of intelligent transportation systems strongly depends on the underlying communication protocols and techniques. In this article, we discuss the current state of the art, trends, and open problems in the area of simulation techniques used to study intervehicle communication (IVC). Here, we touch on a broad range of topics but focus on three aspects that have a strong influence on the degree of realism and hence the reliability of simulation results: the need to integrate microscopic mobility models, the used evaluation metrics, and the impact of human driver behavior on a macroscopic scale. We study and discuss the state of the art of simulation-based performance evaluation of IVC protocols and applications. In the scope of this article, we concentrate on the most recent advances and findings by outlining selected models, techniques, and issues that are specifically related to IVC, with a strong focus on aspects beyond network simulation issues. The main objective is to determine the degree to which available simulation techniques produce realistic results.

Technical Privacy Metrics: a Systematic Survey

The goal of privacy metrics is to measure the degree of privacy enjoyed by users in a system and the amount of protection offered by privacy-enhancing technologies. In this way, privacy metrics contribute to improving user privacy in the digital world. The diversity and complexity of privacy metrics in the literature make an informed choice of metrics challenging. As a result, instead of using existing metrics, new metrics are proposed frequently, and privacy studies are often incomparable. In this survey, we alleviate these problems by structuring the landscape of privacy metrics. To this end, we explain and discuss a selection of over 80 privacy metrics and introduce categorizations based on the aspect of privacy they measure, their required inputs, and the type of data that needs protection. In addition, we present a method on how to choose privacy metrics based on nine questions that help identify the right privacy metrics for a given scenario, and highlight topics where additional work on privacy metrics is needed. Our survey spans multiple privacy domains and can be understood as a general framework for privacy measurement.

Enabling GLOSA for adaptive traffic lights

Green Light Optimized Speed Advisory (GLOSA) systems aim at giving ideal target speed recommendations to the driver when approaching a traffic light to lower CO2 emissions (and fuel consumption) and to reduce the number of unnecessary stops. These systems have been shown to work well with static traffic light programs, unfortunately, a large portion of traffic lights in inner cities are adaptive and can change their behaviour with almost no lead time. This paper presents and validates (using field tests and simulation) a method to help overcome this problem and forecast fully and semi-adaptive traffic lights. First, we transformed the state graph of the traffic light controller into a transition graph focusing on signal changes and their occurrence probability. We then reduced routing possibilities within the graph using real life observations and recorded detector data of the traffic light. We further optimized our system in terms of needed storage and computationally efficiency. Our results show that in 80% of all cases we could predict signal changes 15s in the future with a high enough accuracy to enable GLOSA for adaptive traffic lights.