Modeling and Analysis of Emergency Messaging Delay in Vehicular Ad Hoc Networks

Road crashes, occurring at a high annual rate for many years, demand improvements in transportation systems to provide a high level of on-road safety. Implanting smart sensors, communication capabilities, memory storage and information processing units in vehicles are important components of Intelligent Transportation Systems (ITS). ITS should enable the communication between vehicles and allow cooperative driving and early warnings of sudden breaks and accidents ahead. The prompt availability of the emergency information will provide the driver a time to react in order to avoid possible accidents ahead. Hence, information delivery delay is an importance quality-of-service (QoS) metric in such applications. In this thesis, we focus on modeling the delay for emergency messaging in vehicular ad hoc networks (VANETs). VANETs consist of nodes moving with very high speeds, resulting in frequent topological changes. As a result, many existing models and packet forwarding schemes designed for general purpose mobile ad hoc networks (MANETs) cannot be directly applied to VANETs. In our system model, we consider mobility and traffic density of vehicles. We focus on studying the effect of the traffic flow density on the delay of emergency message dissemination. Hence, traffic flow theories developed by civil engineers form the base of our modeling. The common way of emergency message dissemination in VANETs is broadcasting. To overcome the broadcasting storm problem and improve scalability of such large networks, we adopt a node cluster based broadcasting mechanism. This research provides a realistic mathematical model for the broadcasting delay, which accounts for the randomness in user mobility and matches the highly dynamic nature of VANETs. An investigation on the minimum cluster size that achieves acceptable message delivery latency is provided. It is shown that network control and performance parameters are dependent on the traffic density. Experimental measurement data are used to demonstrate the accuracy of the mathematical modeling

Connected Vehicle Technology: User and System Performance Characteristics

The emerging connected vehicle (CV) technology plays a promising role in providing more operable and safer transportation environments. Yet, many questions remain unanswered as to how various user and system characteristics of CV-enabled networks can shape the successful implementation of the technology to maximize the return on investment. This research attempts to capture the effect of multiple factors such as traffic density, market penetration, and transmission range on the communication stability and overall network performance by developing a new CONnectivity ROBustness (CONROB) model. The model was tested with data collected from microscopic simulation of a 195 sq-mile traffic network and showed a potential to capture the effect of such factors on the communication stability in CV environments. The information exchanged among CVs can also be used to estimate traffic conditions in real time by invoking the probe vehicle feature of CV technology. Since factors affecting the connectivity robustness also have an impact on the performance of traffic condition estimation models, a direct relationship between connectivity robustness and traffic condition estimation performance was established. Simulation results show that the CONROB model can be used as a tool to predict the accuracy of the estimated traffic conditions (e.g. travel times), as well as the reliability of such estimates, given specific system characteristics. The optimal deployment of road-side units (RSUs) is another important factor that affects the communication stability and the traffic conditions estimates and reliability. Thus, an optimization approach was developed to identify the optimal RSUs locations with the objective function of maximizing the connectivity robustness. Simulation results for the developed approach show that CONROB model can help identify the optimal RSUs locations. This shows the importance of CONROB model as a planning tool for CV environments. For the individual user performance characteristics, a preliminary driving simulator test bed for CV technology was developed and tested on thirty licensed drivers. Forward collision warning messages were delivered to drivers when predefined time-to-collision values take place. The findings show improved reaction times of drivers when receiving the warning messages which lend credence to the safety benefits of the CV technology

Interference in vehicle-to-vehicle communication networks - analysis, modeling, simulation and assessment

In wireless vehicular communication networks the periodic transmission of status updates by all vehicles represents a basic service primitive, in particular for safety related applications. Due to the limited communication resources the question raises how much data each node may provide such that the quality of service required by applications can still be guaranteed under realistic interference conditions. Local broadcasts capacity is introduced and analyzed to tackle this open question

Cooperative & cost-effective network selection: a novel approach to support location-dependent & context-aware service migration in VANETs

Vehicular networking has gained considerable interest within the research community and industry. This class of mobile ad hoc network expects to play a vital role in the design and deployment of intelligent transportation systems. The research community expects to launch several innovative applications over Vehicular Ad hoc Networks (VANETs). The automotive industry is supporting the notion of pervasive connectivity by agreeing to equip vehicles with devices required for vehicular ad hoc networking. Equipped with these devices, mobile nodes in VANETs are capable of hosting many types of applications as services for other nodes in the network. These applications or services are classified as safety-critical (failure or unavailability of which may lead to a life threat) and non-safety-critical (failure of which do not lead to a life threat). Safety-critical and non-safety-critical applications need to be supported concurrently within VANETs. This research covers non-safety-critical applications since the research community has overlooked this class of applications. More specifically, this research focuses on VANETs services that are location-dependent. Due to high speed mobility, VANETs are prone to intermittent network connectivity. It is therefore envisioned that location-dependence and intermittent network connectivity are the two major challenges for VANETs to host and operate non-safety-critical VANETs services. The challenges are further exacerbated when the area where the services are to be deployed is unplanned i.e. lacks communication infrastructure and planning. Unplanned areas show irregular vehicular traffic on the road. Either network traffic flows produced by irregular vehicular traffic may lead to VANETs communication channel congestion, or it may leave the communication channel under-utilized. In both cases, this leads to communication bottlenecks within VANETs. This dissertation investigates the shortcomings of location-dependence, intermittent network connectivity and irregular network traffic flows and addresses them by exploiting location-dependent service migration over an integrated network in an efficient and cost-effective manner

Surcoût de l'authentification et du consensus dans la sécurité des réseaux sans fil véhiculaires

Les réseaux ad hoc sans fil véhiculaires (VANET) permettent les communications entre véhicules afin d'augmenter la sécurité routière et d'agrémenter l'expérience de conduite. Une catégorie d'applications ayant suscité un fort intérêt est celle liée à la sécurité du trafic routier. Un exemple prometteur est l'alerte de danger local qui permet d'accroitre la " ligne de vue " du conducteur en lui proposant un ensemble d'alertes afin d'anticiper des situations potentiellement dangereuses. En raison de leurs contraintes temporelles fortes et les conséquences critiques d'une mauvaise utilisation, il est primordial d'assurer des communications sécurisées. Mais l'ajout de services de sécurité entraîne un surcoût de calcul et réseau. C'est pourquoi l'objectif de notre travail est d'établir un cadre général (de manière analytique) du surcoût de la sécurité sur le délai de transfert d'une alerte. Parmi les mécanismes de sécurité conventionnels, le service d'authentification apparaît comme la pierre angulaire de la sécurité des VANETs. De plus, l'authentification est utilisée pour chaque message émis ou reçu. Il est donc potentiellement le service le plus consommateur. C'est pourquoi, nous nous focalisons sur ce service. Nous nous posons ainsi les questions suivantes : quel est le coût de l'authentification ? Quel est son impact sur l'application d'alerte de danger local ? La première contribution de cette thèse est l'élaboration d'une formule permettant le calcul du surcoût de la signature numérique. Mais l'authentification ne sera pas le seul mécanisme de sécurité déployé. Le consensus est notamment un des mécanismes fréquemment employés afin d'instaurer une confiance entre les véhicules. En effet, grâce à une méthode de décision et à partir d'un ensemble de messages, le consensus vise à obtenir un commun accord sur une valeur ou une action entre les véhicules. Ainsi, nous devons comprendre comment définir les paramètres de consensus afin de réduire l'impact de ce mécanisme sur le délai et la distance de freinage ? Comment s'intègre le consensus dans la formule globale de surcoût de l'authentification ? C'est notamment à ces questions que cette thèse répond. Notre deuxième contribution est une méthode de décision dynamique qui analyse l'environnement réseau courant (nombre de voisins à portée de communication), et explore le contenu des alertes. Il en résulte une réduction du nombre de paquets à examiner et donc une réaction plus rapide et plus adaptée à l'alerte.In 2007, road accidents have cost 110 deaths, 4600 injuries and €438 millions daily in the European Union. The damage is similarly devastating in the United States with 102 deaths, 7900 injuries and $630 millions daily. Therefore, industry consortia, governments, and automotive companies, have made the reduction of vehicular fatalities a top priority. To raise this challenge, a main idea is to make vehicles and roads smarter thanks to wireless communications. Indeed, wireless communications will increase the line-of-sight of the driver and make vehicles aware of their environment. Smart vehicles and roads will form a wireless vehicular network (VANET). The VSC Project details 75 applications that could be deployed on vehicular networks. Applications are divided in three categories: safety-related, traffic optimization and infotainment. Automotive safety-related applications aim to assist drivers in avoiding vehicular accidents, by providing advisories and early warnings to drivers, using broadcast vehicle-to-vehicle (V2V) communications. Vehicles typically communicate as per the Dedicated Short Range Communication standard (DSRC), and broadcast messages in response to certain notified events (emergency message) or periodically (beacon message). In this thesis, we focus on V2V communications in Local Danger Warning (LDW) application, which is considered one of the most promising active safety applications for inter-vehicle communication. Since drivers of vehicles participating in V2V communications are expected to act on messages received from other participants, it is clearly necessary that these messages be transmitted in a secure fashion. Unfortunately, security mechanisms come with overhead that impact the performance of the V2V communications, and hence that of the safety applications. The IEEE 1609.2 standard for vehicular ad hoc networks is based on the ECDSA algorithm for supporting the authentication mechanism. The main goal of this work is to define a formula, which assesses the authentication overhead in VANET. We also introduce the problem of consensus, which is an additional mechanism that impacts the total time overhead of ECDSA. Indeed, when you receive a message, you could legitimately ask: "Should I trust this message?". The consensus aims at increasing trust. But consensus mechanism comes with overheads. We investigate the network performance and propose new decision methods and techniques to reduce these overheads

運転支援システムへの共助の導入と有効性の検証

現在までに研究・開発が行われてきた運転支援システムの多くはシステムユーザ自身の安全確保を支援するものであった。しかし、今後は自ら他車両や歩行者といった他者の安全確保に寄与し、他者と協調的に安全な自動車社会を目指すシステムが必要と考えられる。他者の安全確保を支援する活動が上手く適用されている防災分野では、支援活動を自助・共助・公助の3つに分類しており、これらは適切に組み合わせることでより効果を挙げるとされている。一方で自動車分野に目を向けると、現在までに実用化が進んでいる殆どのシステムが自助に、盛んに研究開発が行われている多くのシステムが公助に分類され、自主的に他者を支援する共助の概念が欠落していることが問題点と考えられる。この共助が欠落している状況を補完性の原理に当てはめて考えると、ドライバは自主的に共助でも解決できるはずのリスクに対しても、システムに管理される公助の支援に依存してしまいリスクの認知や払うべき注意が疎かになる。具体的には安全意識や運転能力の低下が起こり易い環境になることが懸念される。道路上を走行する全ての自動車が完全な自動運転にならない限り、ドライバの安全意識や運転能力を衰退させることは交通事故のリスクを増加させることに繋がってしまう。従って、運転支援システムにおいても防災分野と同様に共助の活動を推進していくことで、ドライバの安全やリスクに対する意識を適切に保ちつつ、ドライバが個々では防ぐことが難しいと考えられるリスクに対しても有効な対策を講じることができると考えられる。本研究では交通システム、特に運転支援システムに共助の概念を導入することで、他者からの支援を受けリスクを回避する受援者、他者が危険を回避する為の支援を行う支援者の双方に与える効果を明らかにし、その有効性を検討した。有効性を検討する為のデータはドライビングシミュレータを用いた被験者実験で収集した。受援者側への効果としては、衝突率と衝突速度を有意に低下させ、右直事故のリスクを有意に低下させることが分かった。適切な警告提示のタイミングを検討する為に行った運転行動の解析結果からは、受援者に安全な運転行動を促すためにはドライバが対応可能だが時間的余裕の少ないタイミングでの警告提示が適しており、あまりにも早いタイミングでの警告提示は再加速等の不適切な運転行動を促す危険性があることが明らかになった。一般的には警告が提示されるタイミングが早いほど、受援者がリスクを回避するための時間的余裕が大きくなるので、リスクを軽減する効果が高まると考えられた。しかし早期の警告提示が必ずしも効果的ではないことが確かめられた。支援者側への効果としては、システムの自動化レベルが増すごとに警告提示成功率が有意に上昇し、ドライバに掛かる心理的負荷は有意に減少することが確認された。しかし、共助の大きな特徴であるドライバの意識に着目すると、リスク目標水準を低下させるような安全や運転に対する好ましい意識変化は、ドライバが自主的に行動を起こすことでより強く表れることが確認された。これらの結果から共助システムは、システムからの支援によってドライバの負荷を軽減しつつ、自主性を残すことでドライバの意識変化に働きかけることができる半自動による警告提示が最適という結論に至った。右直事故以外のイベントにも対処し、受援者と支援者の役割が入り混じるような現実に近い状況下で行った実験では心理的負荷が上昇し、それに対応する為にはシステムの自動化レベルを上昇させる必要があることが確かめられた。警告提示に関する認知・判断・操作のフェーズのうち、認知に関しては自動化レベルを上昇させたとしてもリスク目標水準に働きかけるような意識変化が損なわれないことを確認した。従って、判断のフェーズに自主性を残すことで共助の特性を活かせると考えられる。加えて、判断のフェーズに自主性を残した半自動の運転では完全な自動での運転に比べ、交差点進入時に適切な減速操作が行われていたので、ドライバのリスク目標水準を適切に減少させることが出来たと考えられる。今後、世界的に自動運転機能を有した自動車が普及していくことが予測される。しかし、自動運転機能は最初から完全なものではなく徐々に改善され、普及も段階的に進んでいくと考えられる。従って、完全な自動運転までの移行期間においては、ドライバの運転に対する意識を安全に向けさせ、リスク目標水準を低く保つことの重要性はより一層高まると考えられる。本研究で得られた知見が高機能化・自動化の進む今後の自動車社会において、ドライバの意識を適切に保たせる様々な施策の一助となることを願う。電気通信大学201

VANET-enabled eco-friendly road characteristics-aware routing for vehicular traffic

There is growing awareness of the dangers of climate change caused by greenhouse gases. In the coming decades this could result in numerous disasters such as heat-waves, flooding and crop failures. A major contributor to the total amount of greenhouse gas emissions is the transport sector, particularly private vehicles. Traffic congestion involving private vehicles also causes a lot of wasted time and stress to commuters. At the same time new wireless technologies such as Vehicular Ad-Hoc Networks (VANETs) are being developed which could allow vehicles to communicate with each other. These could enable a number of innovative schemes to reduce traffic congestion and greenhouse gas emissions. 1) EcoTrec is a VANET-based system which allows vehicles to exchange messages regarding traffic congestion and road conditions, such as roughness and gradient. Each vehicle uses the messages it has received to build a model of nearby roads and the traffic on them. The EcoTrec Algorithm then recommends the most fuel efficient route for the vehicles to follow. 2) Time-Ants is a swarm based algorithm that considers not only the amount of cars in the spatial domain but also the amoumt in the time domain. This allows the system to build a model of the traffic congestion throughout the day. As traffic patterns are broadly similar for weekdays this gives us a good idea of what traffic will be like allowing us to route the vehicles more efficiently using the Time-Ants Algorithm. 3) Electric Vehicle enhanced Dedicated Bus Lanes (E-DBL) proposes allowing electric vehicles onto the bus lanes. Such an approach could allow a reduction in traffic congestion on the regular lanes without greatly impeding the buses. It would also encourage uptake of electric vehicles. 4) A comprehensive survey of issues associated with communication centred traffic management systems was carried out