Robert Karl Schmidt

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.

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.

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.

The impact of security on cooperative awareness in VANET

Vehicular networking enables new safety applications that aim at improving roads safety. Because of their direct relation to drivers safety, this goal can only be achieved if vehicular networking is based on a technology that is robust against malicious attackers. Therefore, security mechanisms such as authentication are proposed. However, security comes at a cost in terms of computational and communication overhead. For example, a signature and certificate are appended to every beacon sent, which generates an extra load on the network. Moreover, most of the safety applications require a perfect awareness of the vehicles surroundings to perform adequately. To represent such awareness, the Awareness Quality is used to indicate the current level of awareness of the vehicle. This metric was previously used by the Decentralized Congestion Control community to improve channel usage. In this paper, we use the Awareness Quality to investigate the impact of security on cooperative awareness in VANET. Then, we apply this metric to the mechanism of certificate omission, and provide extensive simulation results. The attributes of Awareness Quality metrics enable us to investigate the behavior of certificate omission schemes with a precision that was not provided by aggregate metrics. This enables us to show that congestion-based certificate omission with a quadratic adaption function is the most effective scheme among existing certificate omission schemes.

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.

An approach for selective beacon forwarding to improve cooperative awareness

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.

POPCORN: privacy-preserving charging for emobility

Upcoming years will see a massive deployment of electric vehicles and, combined with this, of charging infrastructure. This will require protocols and standards that will control authentication, authorization, and billing of electric-vehicle charging. The ISO/IEC 15118 protocol that addresses the communication between the charging station and the vehicle is going to play an important role, at least in Europe. While it foresees security protection, there are no significant mechanisms for privacy protection in place. In this paper, we investigate the privacy protection of ISO/IEC 15118 and the surrounding charging and payment infrastructure by means of a Privacy Impact Assessment (PIA). Based on this we propose modular extensions of the protocol applying state-of-the-art Privacy Enhancing Technologies like anonymous credentials to come to a system with maximum privacy protection. We conducted a second PIA to show the benefits to privacy protection that our POPCORN protocol provides compared to the original ISO/IEC 15118. We also describe a proof-of-concept implementation of our system based on a model of electric vehicle and charging station that shows the feasibility of our approach and allows a first preliminary analysis of performance and other issues.

Integrating EVs into the Smart-Grid

Standardization efforts are currently underway to realize the Europe-wide deployment of Smart-Grids. Numerous protocols have already been standardized; each tailored to a distinct application domains. Amongst these, Smart Metering and EV charging have only recently started to converge, and the goal of the PowerUp project has been to advance such convergence. This paper presents the major results from the project. The PowerUp consortium has specified and developed an end-to-end EV to Grid communication system, respecting the applicable communications standards. After introducing the underlying system architecture for the end-to-end integration of the Vehicle-to-Grid (V2G) communications interface, we describe critical Smart-Grid integration aspects for each protocol layer within the V2G communications protocol stack. Finally, prototype test observations are presented. The outlined end-to-end integration of the V2G interface demonstrates the technological solution for ensuring that even mass-deployment of EVs would not interfere with the stability of the electric grid.

A multi-channel Beacon Forwarding approach in dual radio Vehicular Ad-Hoc Networks

Dual radios in Vehicular Ad-Hoc Networks (VANETS) enable the usage of multiple communication chan- nels simultaneously. This results in a higher network capacity in contrast to single radio setups. However, using multiple channels simultaneously leads to Adjacent Channel Interference (ACI) by generating noise in nearby channels. This noise increases the packet loss probability and leads to highly unreliable communication channels. In dual radio setups the impact of ACI is significant e.g. if one radio is receiving on the control channel (CCH) while the other radio performs a transmission on a nearby service channel 2 (SCH2). To reduce ACI on CCH, we propose to use a decreased transmit power on SCH2. However, doing so SCH2 suffers from an increased packet loss probability in contrast to CCH and hence is considered to be a highly unreliable communication channel. To utilize SCH2 and even increase the level of awareness for safety critical applications, we introduce a novel multi channel communication approach using Selective Beacon Forwarding (SBF). Our approach is following the service announcement idea of IEEE 1609.3 [4] and applies forwarding of beacons on SCH2 upon request. We evaluate our scheme called Beacon Forwarding as a Service (BFaaS) based on simulations and show that it increases the level of awareness by up to 50% compared to common beaconing strategies.

Decentralized Congestion Control Techniques for VANETs

Direct vehicle-to-vehicle (V2V) communication must operate reliably and with low latency under all circumstances to allow for imminent collision prevention. However, the amount of data to be exchanged is limited by the physical limitations of the communication channel. In vehicular ad hoc networks (VANETs), this limitation is particularly relevant when vehicle density rises and thus lots of information needs to be exchanged, bringing the communication system into a congested state. Rapidly changing topology, channel characteristics, distributed medium access, and challenging active safety application requirements cause many challenges to the resource management. This chapter reviews these issues to motivate suitable Decentralized Congestion Control (DCC) algorithms and cross-layer coordination mechanisms. In particular, it is shown that performance degradations like packet losses, the reduction of the effective communication range, and packet transmission delays are correlated with the channel load. The strategy of the DCC is to avoid these degradations by limiting the load offered by each vehicle to the radio channel, such that a certain channel load threshold is not significantly exceeded. This mitigates the communication range degradation and keeps the packet latencies moderate. The DCC is already part of specifications in the European Telecommunications Standards Institute (ETSI), e.g. ETSI TS 102 687.