Inter-vehicle communication (IVC) systems (i.e., systems not relying on roadside infrastructure) have the potential to radically improve the safety, efficiency, and comfort of everyday road travel. Their main advantage is that they bypass the need for expensive infrastructure; their major drawback is the comparatively complex networking protocols and the need for significant penetration before their applications can become effective. In this article we present several major classes of applications and the types of services they require from an underlying network. We then proceed to analyze existing networking protocols in a bottom-up fashion, from the physical to the transport layers, as well as security aspects related to IVC systems. We conclude the article by presenting several projects related to IVC as well as a review of common performance evaluation techniques for IVC systems.

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Inter-vehicle communication systems: a survey

Simulation and emulation are valuable techniques for the evaluation of algorithms and protocols used in mobile ad-hoc networks. However, these techniques always require the simplification of real-world properties such as radio characteristics or node mobility. It has been shown that this may lead to results and conclusions which do not reflect the behavior of ad-hoc networks in the real world. Various prototype implementations demonstrate that even simple protocols such as flooding do not behave as it was predicted by earlier simulation. To overcome this problem, real-world experiments are required. In this paper, we present a survey on existing real-world implementations of mobile ad-hoc networks. We report on the technology used for the implementations as well as on key findings from experiments conducted with these implementations.

A survey on real-world implementations of mobile ad-hoc networks

Car-to-car communication by means of wireless technology shows a strong potential to enhance both safety and comfort of road users. The necessity to reach cars beyond the transmission range of the own radio creates the challenge to find algorithms to efficiently forward packets. In these so-called vehicular ad hoc networks, position information has been identified as a crucial component that alleviates some of the limitations of existing topology-based protocols. Thus, we see the use of positional information at the core of a car-to-car communication system that provides advanced applications for active safety, distributed floating car data, as well as user communication and information. A major thrust to leverage a car-to-car communication platform was provided by the FleetNet project, partly funded by the German Ministry of Education and Research BMB+F and led by DaimlerChrysler AG. Based on ad hoc networking principles and the availability of position information, the project developed suitable communication concepts. In addition to simulation studies, a prototype communication and application system was implemented and deployed, embedding safety and convenience applications. With car-based real world field trials successfully conducted, first results and experiences look promising.

FleetNet: Bringing Car-to-Car Communication into the Real World

--- This paper evaluates the usefulness of watchdog modules for intrusion detection. A watchdog is the basic component for the construction of most of the intrusion detection systems proposed so far for self-organizing wireless networking systems like VANETs. Contributions of this work are threefold. First, the component is designed to be protocol independent, thus compatible with any different types of ad hoc routing protocols. Second, it encompasses a high detection coverage with a low detection latency. Third, the previous properties are guaranteed while minimizing the number of generated false positives and negatives The provided design is implemented and evaluated. Results show that a set of trade-offs must be adopted in order to obtain an acceptable balance between the coverage and detection latency of the watchdog and the resources required from devices.

Evaluating the Usefulness of Watchdogs for Intrusion Detection in VANETs

The UN Economic Commission's Statistics of Road Traffic Accidents report of 2011 shows that every year, about 150 000 human beings lose their lives on the roads of the western world. Although it is a common belief that this figure could shrink with the use of new sensor and communication technologies, unfortunately, none such systems have hit the road to date. Ideally, if such technologies were put into place, vehicles could be part of a vehicular ad hoc network (VANET) capable of spreading relevant information about dangerous events (e.g., car accidents) to all approaching drivers. However, all this is mainly supported by simulation studies, as no practical results have been published to date, revealing the effective performances of such systems at work. In this paper, we fill this gap, presenting a detailed description of the greatest experiments (a few thousand throughout the streets of Los Angeles), to date, ever performed with an accident warning system specifically devised for highway scenarios. In particular, among all the possible candidate schemes, we ran a few thousand experiments with the accident warning system algorithm that was proven to be optimal in terms of bandwidth usage and covered distance in realistic scenarios. Our experiments confirm what has been observed before in theory and simulation, i.e., the use of such a system can reduce, by as much as 40%, the amount of vehicles involved in highway pileups.

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Safe Driving in LA: Report from the Greatest Intervehicular Accident Detection Test Ever

Within the framework of the FLEETNET project, a real-world ad hoc network testbed was built using cars as mobile nodes. These cars were equipped with computing and communication devices. As ad hoc routing algorithm, position-based forwarding implemented on Linux-based laptops was used, exploiting position information gathered by on-board navigation systems. We report on measurements and experiences with this testbed for static 1-hop and 3-hop scenarios as well as for mobile 3-hop scenarios. Beside the power, loss-rate, throughput and delivery ratio measurements, we present our methodology for conducting experiments with 'real-world' mobile ad hoc networks and discuss problems of beacon-based position-based routing due to radio fluctuations.

M. Moske

Papers

Performance measurements of a vehicular ad hoc network