ne of the major goals of vehicular ad hoc networks (VANETs) is to support traffic safety. Cooperative awareness applications require frequent and low-delay information exchange among vehicles, including data such as current position, movement, and acceleration. This is realized by broadcasting socalled (single-hop) beacon messages. As a result, every vehicle is aware of other vehicles within a certain range. Beaconing is also the basic supporting process that enables geographic routing and message dissemination. However, this also requires a significant amount of bandwidth. The higher the frequency and thus the accuracy, the higher the bandwidth consumption.The first phase of research on VANETs has set the boundary conditions in terms of basic communication protocols and routing paradigms. Communication in VANETs will be based on IEEE 802.11p. Message dissemination and routing are based on geocast principles. Beaconing takes place on a single communication channel (commonly referred to as the control channel) that is shared by all nodes.However, it has also been shown in [1] that the limited bandwidth of the wireless channel has a severe impact on the efficiency of the communication. This means that if the beacon rate is fixed, channel load may increase too much in scenarios with high vehicle density. High channel utilization increases the information loss as packets are received erroneously, which is especially observed at large distances between sender and receiver.Simply reducing the beacon rate is not a suitable solution because it reduces the information quality at the same time. The error between the real position of a vehicle and the last known position retrieved from a beacon increases as the beacon rate is reduced. This results in position inaccuracies, which may disturb correct operation of active safety applications, which rely on accurate and up-to-date information.Currently, there is no final recommendation for a particular static beacon rate. No upper boundary in terms of maximum channel load has been specified. Furthermore, no requirements from the different applications have yet been clearly defined. As a consequence, even minimum and maximum beacon rate are hard to derive as these two boundaries have to satisfy all imaginable road traffic situations.In this article we pave the way for further enhancements of beaconing algorithms for the second phase of research on VANETs. After a short assessment of the current state of the art, we present a detailed analysis of the problem space and how different beacon rates influence 1) the offered load to the channel and 2) the resulting average and maximum accuracy of information Based on this problem evaluation, we motivate a flexible approach to control both appropriately. For this purpose, we propose a situation adaptive beaconing process that adapts the beacon rate continuously. The design space and different candidates for such an algorithm are introduced in this article. AbstractIn the future intervehicle communication will make driving safer, easier...

5G promises many new vertical service areas beyond simple communication and data transfer. We propose CPCL (cooperative passive coherent location), a distributed MIMO radar service, which can be offered by mobile radio network operators as a service for public user groups. CPCL comes as an inherent part of the radio network and takes advantage of the most important key features proposed for 5G. It extends the well-known idea of passive radar (also known as passive coherent location, PCL) by introducing cooperative principles. These range from cooperative, synchronous radio signaling, and MAC up to radar data fusion on sensor and scenario levels. By using software-defined radio and network paradigms, as well as real-time mobile edge computing facilities intended for 5G, CPCL promises to become a ubiquitous radar service which may be adaptive, reconfigurable, and perhaps cognitive. As CPCL makes double use of radio resources (both in terms of frequency bands and hardware), it can be considered a green technology. Although we introduce the CPCL idea from the viewpoint of vehicle-tovehicle/infrastructure (V2X) communication, it can definitely also be applied to many other applications in industry, transport, logistics, and for safety and security applications.Index Terms-5G verticals, vehicle-to-x (V2X), cooperative driving, intelligent transport systems (ITS), joint communication and radar, passive coherent location (PCL), passive OFDM radar, distributed MIMO radar network, radar resource management, high-resolution radar parameter estimation All authors are with the Technische Universität Ilmenau (Ilmenau University of Technology). Carsten Andrich, Michael Döbereiner, and Giovanni Del Galdo are with the Fraunhofer IIS.

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Communication using VANETs is commonly seen as the next milestone for improving traffic safety. Vehicles will be enabled to exchange any kind of information that helps to detect and mitigate dangerous situations. Security research in the past years has shown that VANETs are endangered by a plethora of severe security risk.Subject of this work is the modeling of attackers that target active safety applications in VANETs. Through a risk analysis, this work identifies assets, threats and potential attacks in inter-vehicle communication. The risk analysis shows that the most serious threat arises from a quasi-stationary (road-side) attacker that distributed forged warning messages. This attacker is discussed more deeply. We show the degrees of freedom that are available for position forging and find thereby two attacks that demand attention: single position forging having low effort compared to sophisticated movement path forging having a potentially high influence on road traffic safety. I. INTRODUCTIONVehicular Ad-Hoc Networks (VANETs) describe the technology of direct communication among vehicles themselves as well as among vehicles and (roadside) infrastructure. They enable vehicles to exchange information in order to increase vehicle passenger safety and road safety, traffic efficiency and driver convenience. Such information are enhancing autonomous in-vehicle safety systems as well as they are informing the driver of relevant events where his reaction or attention is required. Thus, the information received by a vehicle must be secure and reliable, meaning that information security is a crucial part of such a system. Information security and hence drivers' safety is endangered once there is a vulnerability in the system attracting attackers who exploit the vulnerability according to their motivation. For example, the open system character of VANETs might motivate attackers to interfere with the system. This interference may even provoke wrong driving maneuvers leading to an accident in the worst case.Attacks on VANETs have been summarized generally in previous work [1]. Several solutions have been proposed to secure the system against a variety of these attacks. What is missing so far is an in-depth discussion and analysis of attackers and the modeling of attacker behavior to analyze and to help to improve the proposed security solutions.The early stage of development of VANETs does not allow for a meaningful attack analysis. Currently, there are still too many options with respect to protocols and applications. Modeling all possible attacker behaviors and attacks on these would be impossible. Therefore, we reduce the options by

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Abstract-Cooperative awareness is established by vehicles exchanging their status frequently. In situations where a high number of vehicles access the communication channel with high frequency, communication and cooperative awareness suffer from increased packet loss.So far, forwarding of beacons focuses on extending the range of V2V communication which is not necessarily needed in most scenarios. In this paper, we motivate selective beacon forwarding to improve the reliability of cooperative awareness in high load situations. We define a metric to measure the quality of cooperative awareness and compare different static beacon rates by a simulation study. Especially in high load situations, we evaluate selective forwarding of beacons to overcome the awareness degradation due to interference, leading to packet loss even at short distances. We show that our approach causes only slight overhead in terms of additional messages and that the age of forwarded information is less than half the beacon interval.

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