Tim Leinmüller

Exploration of adaptive beaconing for efficient intervehicle safety communication

In the future intervehicle communication will make driving safer, easier, and more comfortable. As a cornerstone of the system, vehicles need to be aware of other vehicles in the vicinity. This cooperative awareness is achieved by beaconing, the exchange of periodic single-hop broadcast messages that include data on the status of a vehicle. While the concept of beaconing has been developed in the first phase of research on VANETs, recent studies have revealed limitations with respect to network performance. Obviously, the frequency of beacon messages directly translates into accuracy of cooperative awareness and thus traffic safety. There is an indisputable trade-off between required bandwidth and achieved accuracy. In this work we analyze this trade-off from different perspectives considering the consequences for safety applications. As a solution to the problem of overloading the channel, we propose to control the offered load by adjusting the beacon frequency dynamically to the current traffic situation while maintaining appropriate accuracy. To find an optimal adaptation, we elaborate on several options that arise when determining the beacon frequency. As a result, we propose situation-adaptive beaconing. It depends on the vehicles own movement and the movement of surrounding vehicles, macroscopic aspects like the current vehicle density, or microscopic aspects.

POSITION VERIFICATION APPROACHES FOR VEHICULAR AD HOC NETWORKS

Intervehicle communication is regarded as one of the major applications of mobile ad hoc networks (MANETs). Compared to MANETs, these so-called vehicular ad hoc networks (VANETs) have special requirements in terms of node mobility and position-dependent applications, which are well met by geographic routing protocols. Functional research on geographic routing has already reached a considerable level, whereas security aspects have been vastly neglected so far. Since position dissemination is crucial for geographic routing, forged position information has severe impact regarding both performance and security. In this work, we first analyze the problems that may arise from falsified position data. Then, in order to lessen these problems, we propose detection mechanisms that are capable of recognizing nodes cheating about their location in position beacons. In contrast to other position verification approaches, our solution does not rely on special hardware or dedicated infrastructure. Evaluation based on simulations shows that our position verification system successfully discloses nodes disseminating false positions and thereby widely prevents attacks using position cheating

Abiding geocast: time--stable geocast for ad hoc networks

Abiding geocast is a time stable geocast delivered to all nodes that are inside a destination region within a certain period of time. Services like position--based advertising, position--based publish--and--subscribe, and many other location--based services profit from abiding geocast. For vehicular ad hoc networks, abiding geocast allows realization of information and safety applications like virtual warning signs. Similar to real traffic or warning signs, they are attached to a certain geographical position or area. When a vehicle enters such an area, the virtual warning sign is displayed for the driver.This paper discusses the design space, the semantics, and three reasonable approaches for abiding geocast in an ad hoc network. The first one is a server solution to store the messages. The second approach stores the messages at an elected node inside the geocast destination region that temporarily acts as a server. The last one complements the exchange of neighbor information necessary for many unicast routing protocols with abiding geocast information.We compare the proposed protocols with a probabilistic network load and delivery success ratio analysis. The results show that the approaches with local message storage cause less network load. However, we also observed that in some cases the delivery success ratio of the approaches with local message storage is lower.

Trust Issues for Vehicular Ad Hoc Networks

Characteristics and requirements of vehicular ad hoc networks (VANETs) differ quite significantly compared to standard ad hoc networks. Especially trust in VANETs is very important but still open issue, which will be addressed in this paper. We will describe, discuss and assess approaches and concepts that were proposed in ordinary fixed networks and mobile ad hoc networks and will show weak and strong spots. As basis for our considerations, we will describe a detailed automotive scenario, which relies on inter-vehicle communication for the exchange of safety relevant warning messages.

Impact of pseudonym changes on geographic routing in VANETs

Inter-vehicle communication is regarded as one of the major applications of mobile ad hoc networks (MANETs). In these so called vehicular ad hoc networks (VANETs) security and privacy are crucial factors for successful deployment. In a scenario, where each vehicle would have a unique identifier, eavesdroppers could easily accumulate location profiles. As a solution approach, several authors suggest using changeable pseudonyms as temporary vehicle identifiers. If a vehicle changes its pseudonym from time to time, long-term tracking can be avoided. However, as we show in this paper, changing identifiers has detrimental effects on routing efficiency and increases packet loss. So, designers of VANET systems need to aim for a balance between privacy protection on the one and performance on the other hand. The results of this paper provide advise on how to achieve this balance.

Degradation of Transmission Range in VANETs caused by Interference

ABSTRACT Reliability is one of the key requirements for inter-vehicle communication in order to improve safety in road traffic. This paper describes the difficulties of inter-vehicle communication. We focus on an analysis of the state-of-the art MAC protocol draft IEEE P802.11p and its limitations in high load situations. For our analysis we consider a particular safety scenario: An emergency vehicle is approaching a traffic jam. In a simulation experiment, we highlight that severe packet loss can occur. The reliable transmission range can be reduced by up to 90%. The main reason for this degradation is interference caused by transmissions of other vehicles within the traffic jam. In the study, we focus on the vehicle at the very end of the traffic jam. There, we measure the number of packets per second that are successfully received from the emergency vehicle. The key observation is that only a small fraction of the warning lead time remains which will also reduce the time for the driver to react on this information on an approaching emergency vehicle.

Secure and efficient beaconing for vehicular networks

The basis for many VANET applications are periodic beacons carrying information like location, heading and speed. In order to secure beaconing, messages should be signed and carry a certificate to attest valid network participants. In order to reduce the significant communication and computational overhead created by this, we propose to skip signatures or certificates in certain situations.

Modeling Roadside Attacker Behavior in VANETs

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.

Influence of falsified position data on geographic ad-hoc routing

There has been a lot of effort in the research on routing in mobile ad hoc networks in the last years. Promising applications of MANETs, e.g. in the automotive domain, are the drive for the design of inter-vehicle networks. So far, several projects in this field have chosen geographic routing approaches because of their outstanding performance and the possibility to support location-based applications like traffic warning functions. Having reached a reasonable functional level, a next step will be a deeper study of safety and security issues. With this paper, we dive into that area by assuming defective or malicious nodes that disseminate wrong position data. First, we have a look at the local problems that may arise from falsified position data, then we show the global effects on the routing performance by simulating malicious nodes. Simulation results show that the overall ratio of successfully delivered messages decreases, depending on the number of maliciously acting nodes, even up to approximately 30%. We conclude from this result that future work should take these threats into account in order to design more robust routing protocols.

Advanced carrier sensing to resolve local channel congestion

Communication performance in VANETs under high channel load is significantly degraded due to packet collisions and messages drops, also referred to as local channel congestion. So far, research was focused on the control of transmit power and the limitation of the messages rate to mitigate the effects of high load. Few attention has been paid to the carrier sensing setup, i.e controlling WHEN the channel is indicated as clear. In previous work, we identified that the Clear Channel Assessment (CCA) as part of the carrier sensing is a very efficient way of controlling the spatial reuse under high load. The CCA threshold determines at which received power level the channel is sensed busy. In this paper, we propose a stepwise CCA Threshold Adjustment (CTA) depending on how long the packet has been waiting already for medium access. This basic and robust approach mitigates significantly the problem of local message queue drops and hence local congestion. The simulation study confirms the reduction of the average and maximum medium access delay as well as the prevention of message queue drops. Even under inaccurate CCA thresholds among the vehicles, fairness in medium access can be maintained by using CTA. In all cases, the awareness of each vehicle is dramatically improved within the safety-critical area of each vehicle.