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 vehicle's own movement and the movement of surrounding vehicles, macroscopic aspects like the current vehicle density, or microscopic aspects

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

Degradation of transmission range in VANETs caused by interference

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

Improved Security in Geographic Ad Hoc Routing Through Autonomous Position Verification

Inter-vehicle communication is regarded as one of the major applications of mobile ad hoc networks (MANETs). Compared to other 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 order to lessen this problem, we propose a detection mechanism that is capable of recognizing nodes cheating about their position in beacons (periodic position dissemination in most single-path geographic routing protocols, e.g. GPSR). Unlike other proposals described in the literature, our detection does not rely on additional hardware or special nodes, which contradicts the ad hoc approach. Instead, this mechanism uses a number of different independent sensors to quickly give an estimation of the trustworthiness of other nodes ’ position claims without using dedicated infrastructure or specialized hardware. The simulative evaluation proves that our position verification system successfully discloses nodes disseminating false positions and thereby widely prevents attacks using position cheating

Security Requirements and Solution Concepts in Vehicular Ad Hoc Networks

Inter-vehicle communication is one of the most challenging research areas for communication in wireless ad hoc and sensor networks. The main benefit of this kind of communication is seen in active safety systems, which aim at increasing passengers’ safety by exchanging warning messages between vehicles. In the past few years, considerable effort has been spent in research on networking protocols and applications, however research on security threats and solutions only started recently. In this paper, we elaborate on security issues in vehicular ad-hoc networks (VANETs) regarding active safety applications. We provide an overview on solution concepts and evaluate requirements of corresponding mechanisms. One conclusion is that although some concepts can be viewed as strong solutions from a network point of view, they do not fit into the design constraints of VANETs. Therefore, less secure mechanisms will probably have to suffice

Greedy routing in highway scenarios: The impact of position faking nodes

have been an active research domain during the past few years. Work so far focused on routing and applications, however, research on security issues has been started only recently. One of the fundamental results of past and ongoing research projects in the domain of vehicular ad-hoc networks is the usage of geographic routing protocols. On the one hand this is due to the fact that they are well suited to highly dynamic network topologies. On the other hand VANETs are assumed to provide location based services, which would also benefit from position aware routing. In this paper, we analyze the potential impact of false position information in beacon messages on geographic routing. We assume that false position information is distributed either by malicious nodes or by defective nodes. For the analysis, we focus on highway scenarios with respective vehicular movement patterns. Our results show severe performance degradation even in case there is only a low percentage (10%) of maliciously acting nodes that combine position information falsification with subsequent message dropping. Index Terms—Vehicular ad hoc networks (VANETs), position dependent routing, security I