Vehicular networking is envisioned to be a key technology area for significant growth in the coming years. Although the expectations for this emerging technology are set very high, many practical aspects remain still unsolved for a vast deployment of vehicular networks. This dissertation addresses the enabling physical layer techniques to meet the challenges in vehicular networks operating in mobile wireless environments. Considering the infrastructure-less nature of vehicular networks, we envision cooperative diversity well positioned to meet the demanding requirements of vehicular networks with their underlying distributed structure. Cooperative diversity has been proposed as a powerful means to enhance the performance of high-rate communications over wireless fading channels. It realizes spatial diversity advantages in a distributed manner where a node uses others antennas to relay its message creating a virtual antenna array. Although cooperative diversity has garnered much attention recently, it has not yet been fully explored in the context of vehicular networks considering the unique characteristics of vehicular networks, this dissertation provides an error performance analysis study of cooperative transmission schemes for various deployment and traffic scenarios. In the first part of this dissertation, we investigate the performance of a cooperative vehicle-to-vehicle (V2V) system with amplify-and-forward relaying for typical traffic scenarios under city/urban settings and a highway area. We derive pairwise error probability (PEP) expressions and demonstrate the achievable diversity gains. The effect of imperfect channel state information (CSI) is also studied through an asymptotical PEP analysis. We present Monte-Carlo simulations to confirm the analytical derivations and present the error rate performance of the vehicular scheme with perfect and imperfect-CSI. In the second part, we consider road-to-vehicle (R2V) communications in which roadside access points use cooperating vehicles as relaying terminals. Under the assumption of decode-and-forward relaying, we derive PEP expressions for single-relay and multi-relay scenarios. In the third part, we consider a cooperative multi-hop V2V system in which direct transmission is not possible and investigate its performance through the PEP derivation and diversity gain analysis. Monte-Carlo simulations are further provided to con firm the analytical derivations and provide insight into the error rate performance improvement.

Vehicular networking is envisioned to be a key technology area for significant growth in the coming years. Although the expectations for this emerging technology are set very high, many practical aspects remain still unsolved for a vast deployment of vehicular networks. This dissertation addresses the enabling physical layer techniques to meet the challenges in vehicular networks operating in mobile wireless environments. Considering the infrastructure-less nature of vehicular networks, we envision cooperative diversity well positioned to meet the demanding requirements of vehicular networks with their underlying distributed structure. Cooperative diversity has been proposed as a powerful means to enhance the performance of high-rate communications over wireless fading channels. It realizes spatial diversity advantages in a distributed manner where a node uses others antennas to relay its message creating a virtual antenna array. Although cooperative diversity has garnered much attention recently, it has not yet been fully explored in the context of vehicular networks considering the unique characteristics of vehicular networks, this dissertation provides an error performance analysis study of cooperative transmission schemes for various deployment and traffic scenarios. In the first part of this dissertation, we investigate the performance of a cooperative vehicle-to-vehicle (V2V) system with amplify-and-forward relaying for typical traffic scenarios under city/urban settings and a highway area. We derive pairwise error probability (PEP) expressions and demonstrate the achievable diversity gains. The effect of imperfect channel state information (CSI) is also studied through an asymptotical PEP analysis. We present Monte-Carlo simulations to confirm the analytical derivations and present the error rate performance of the vehicular scheme with perfect and imperfect-CSI. In the second part, we consider road-to-vehicle (R2V) communications in which roadside access points use cooperating vehicles as relaying terminals. Under the assumption of decode-and-forward relaying, we derive PEP expressions for single-relay and multi-relay scenarios. In the third part, we consider a cooperative multi-hop V2V system in which direct transmission is not possible and investigate its performance through the PEP derivation and diversity gain analysis. Monte-Carlo simulations are further provided to con firm the analytical derivations and provide insight into the error rate performance improvement.

Throughout the last decade, vehicle localization has been attracting significant attention in a wide range of applications, including Navigation Systems, Road Tolling, Smart Parking, and Collision Avoidance. To deliver on their requirements, these applications need specific localization accuracy. However, current localization techniques lack the required accuracy, especially for mission critical applications. Although various approaches for improving localization accuracy have been reported in the literature, there is still a need for more efficient and more effective measures that can ascribe some level of accuracy to the localization process. These measures will enable localization systems to manage the localization process and resources so as to achieve the highest accuracy possible, and to mitigate the impact of inadequate accuracy on the target application. In this thesis, a framework for fusing different localization techniques is introduced in order to estimate the location of a vehicle along with location integrity assessment that captures the impact of the measurement conditions on the localization quality. Knowledge about estimate integrity allows the system to plan the use of its localization resources so as to match the target accuracy of the application. The framework introduced provides the tools that would allow for modeling the impact of the operation conditions on estimate accuracy and integrity, as such it enables more robust system performance in three steps. First, localization system parameters are utilized to contrive a feature space that constitutes probable accuracy classes. Due to the strong overlap among accuracy classes in the feature space, a hierarchical classification strategy is developed to address the class ambiguity problem via the class unfolding approach (HCCU). HCCU strategy is proven to be superior with respect to other hierarchical configuration. Furthermore, a Context Based Accuracy Classification (CBAC) algorithm is introduced to enhance the performance of the classification process. In this algorithm, knowledge about the surrounding environment is utilized to optimize classification performance as a function of the observation conditions. Second, a task-driven integrity (TDI) model is developed to enable the applications modules to be aware of the trust level of the localization output. Typically, this trust level functions in the measurement conditions; therefore, the TDI model monitors specific parameter(s) in the localization technique and, accordingly, infers the impact of the change in the environmental conditions on the quality of the localization process. A generalized TDI solution is also introduced to handle the cases where sufficient information about the sensing parameters is unavailable. Finally, the produce of the employed localization techniques (i.e., location estimates, accuracy, and integrity level assessment) needs to be fused. Nevertheless, these techniques are hybrid and their pieces of information are conflicting in many situations. Therefore, a novel evidence structure model called Spatial Evidence Structure Model (SESM) is developed and used in constructing a frame of discernment comprising discretized spatial data. SESM-based fusion paradigms are capable of performing a fusion process using the information provided by the techniques employed. Both the location estimate accuracy and aggregated integrity resultant from the fusion process demonstrate superiority over the employing localization techniques. Furthermore, a context aware task-driven resource allocation mechanism is developed to manage the fusion process. The main objective of this mechanism is to optimize the usage of system resources and achieve a task-driven performance. Extensive experimental work is conducted on real-life and simulated data to validate models developed in this thesis. It is evident from the experimental results that task-driven integrity assessment and control is applicable and effective on hybrid localization systems.

This licentiate thesis work investigates two medium access control (MAC) methods, when used in traffic safety applications over vehicular ad hoc networks (VANETs). The MAC methods are carrier sense multiple access (CSMA), as specified by the leading standard for VANETs IEEE 802.11p, and self-organizing time-division multiple access (STDMA) as used by the leading standard for transponders on ships. All vehicles in traffic safety applications periodically broadcast cooperative awareness messages (CAMs). The CAM based data traffic implies requirements on a predictable, fair and scalable medium access mechanism. The investigated performance measures are channel access delay, number of consecutive packet drops and the distance between concurrently transmitting nodes. Performance is evaluated by computer simulations of a highway scenario in which all vehicles broadcast CAMs with different update rates and packet lengths. The obtained results show that nodes in a CSMA system can experience unbounded channel access delays and further that there is a significant difference between the best case and worst case channel access delay that a node could experience. In addition, with CSMA there is a very high probability that several concurrently transmitting nodes are located close to each other. This occurs when nodes start their listening periods at the same time or when nodes choose the same backoff value, which results in nodes starting to transmit at the same time instant. The CSMA algorithm is therefore both unpredictable and unfair besides the fact that it scales badly for broadcasted CAMs. STDMA, on the other hand, will always grant channel access for all packets before a predetermined time, regardless of the number of competing nodes. Therefore, the STDMA algorithm is predictable and fair. STDMA, using parameter settings that have been adapted to the vehicular environment, is shown to outperform CSMA when considering the performance measure distance between concurrently transmitting nodes. In CSMA the distance between concurrent transmissions is random, whereas STDMA uses the side information from the CAMs to properly schedule concurrent transmissions in space. The price paid for the superior performance of STDMA is the required network synchronization through a global navigation satellite system, e.g., GPS. That aside since STDMA was shown to be scalable, predictable and fair; it is an excellent candidate for use in VANETs when complex communication requirements from traffic safety applications should be met.

The C2X Communication is of high interest to the automotive industry. Ongoing research on this topic mainly bases on the simulation of Vehicular Ad Hoc Networks. In order to estimate the necessary level of simulation details their impact on the results needs to be examined. This thesis focuses on different channel models as the freespace, shadowing, and Ricean model, along with varying parameters. For these simulations the network simulator ns-2 is extended to provide IEEE 802.11p compliance. However, the WAVE mode is not considered since it is still under development and not finally approved. Besides a more sophisticated packet error model than the existing implementation, as well as a link adaptation algorithm, is added. In this thesis several simulations examine specific details of wireless communication systems such as fairness of multiple access, interferences, throughput, and variability. Furthermore, the simulation points out some unexpected phenomena as starving nodes and saturation effects in multi hop networks. Those led to the conclusion that the IEEE 802.11 draft amendment does not solve known problems of the original IEEE 802.11 standard.

La convergencia de las telecomunicaciones, la informática, la tecnología inalámbrica y los sistemas de transporte, va a facilitar que nuestras carreteras y autopistas nos sirvan tanto como plataforma de transporte, como de comunicaciones. Estos cambios van a revolucionar completamente cómo y cuándo vamos a acceder a determinados servicios, comunicarnos, viajar, entretenernos, y navegar, en un futuro muy cercano. Las redes vehiculares ad hoc (vehicular ad hoc networks VANETs) son redes de comunicación inalámbricas que no requieren de ningún tipo de infraestructura, y que permiten la comunicación y conducción cooperativa entre los vehículos en la carretera. Los vehículos actúan como nodos de comunicación y transmisores, formando redes dinámicas junto a otros vehículos cercanos en entornos urbanos y autopistas. Las características especiales de las redes vehiculares favorecen el desarrollo de servicios y aplicaciones atractivas y desafiantes. En esta tesis nos centramos en las aplicaciones relacionadas con la seguridad. Específicamente, desarrollamos y evaluamos un novedoso protocol que mejora la seguridad en las carreteras. Nuestra propuesta combina el uso de información de la localización de los vehículos y las características del mapa del escenario, para mejorar la diseminación de los mensajes de alerta. En las aplicaciones de seguridad para redes vehiculares, nuestra propuesta permite reducir el problema de las tormentas de difusión, mientras que se mantiene una alta efectividad en la diseminación de los mensajes hacia los vehículos cercanos. Debido a que desplegar y evaluar redes VANET supone un gran coste y una tarea dura, la metodología basada en la simulación se muestra como una metodología alternativa a la implementación real. A diferencia de otros trabajos previos, con el fin de evaluar nuestra propuesta en un entorno realista, en nuestras simulaciones tenemos muy en cuenta tanto la movilidad de los vehículos, como la transmisión de radio en entornos urbanos, especialmente cuando los edificios interfieren en la propagación de la señal de radio. Con este propósito, desarrollamos herramientas para la simulación de VANETs más precisas y realistas, mejorando tanto la modelización de la propagación de radio, como la movilidad de los vehículos, obteniendo una solución que permite integrar mapas reales en el entorno de simulación. Finalmente, evaluamos las prestaciones de nuestro protocolo propuesto haciendo uso de nuestra plataforma de simulación mejorada, evidenciando la importancia del uso de un entorno de simulación adecuado para conseguir resultados más realistas y poder obtener conclusiones más significativas. / Martínez Domínguez, FJ. (2010). Improving Vehicular ad hoc Network Protocols to Support Safety Applications in Realistic Scenarios [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/9195

Le routage et la gestion des clés sont les plus grands défis dans les réseaux de véhicules. Un comportement de routage inapproprié peut affecter l’efficacité des communications et affecter la livraison des applications liées à la sécurité. D’autre part, la gestion des clés, en particulier en raison de l’utilisation de la gestion des certificats PKI, peut entraîner une latence élevée, ce qui peut ne pas convenir à de nombreuses applications critiques. Pour cette raison, nous proposons deux modèles de confiance pour aider le protocole de routage à sélectionner un chemin de bout en bout sécurisé pour le transfert. Le premier modèle se concentre sur la détection de noeuds égoïstes, y compris les attaques basées sur la réputation, conçues pour compromettre la «vraie» réputation d’un noeud. Le second modèle est destiné à détecter les redirecteurs qui modifient le contenu d’un paquet avant la retransmission. Dans la gestion des clés, nous avons développé un système de gestion des clés d’authentification et de sécurité (SA-KMP) qui utilise une cryptographie symétrique pour protéger la communication, y compris l’élimination des certificats pendant la communication pour réduire les retards liés à l’infrastructure PKI. / Routing and key management are the biggest challenges in vehicular networks. Inappropriate routing behaviour may affect the effectiveness of communications and affect the delivery of safety-related applications. On the other hand, key management, especially due to the use of PKI certificate management, can lead to high latency, which may not be suitable for many time-critical applications. For this reason, we propose two trust models to assist the routing protocol in selecting a secure end-to-end path for forwarding. The first model focusses on detecting selfish nodes, including reputation-based attacks, designed to compromise the “true” reputation of a node. The second model is intended to detect forwarders that modify the contents of a packet before retransmission. In key management, we have developed a Secure and Authentication Key Management Protocol (SA-KMP) scheme that uses symmetric cryptography to protect communication, including eliminating certificates during communication to reduce PKI-related delays.

Chaque année en Europe, 1.300.000 accidents de la route ont comme conséquence 1.700.000 blessés. Le coût financier d’accidents de la route est évalué à 160 milliards d’euros (approximativement le même coût aux Etats-Unis). VANET (Vehicular Ad-hoc NETwork) est une des technologies clés qui peut permettre de réduire d’une façon significative le nombre d’accidents de la route (e.g. message d’urgence signalant la présence d’un obstacle ou d’un véhicule en cas de brouillard). En plus de l’amélioration de la sécurité et du confort des conducteurs et des passagers, VANET peut contribuer à beaucoup d’applications potentielles telles que la prévision et la détection d’embouteillages, la gestion d’infrastructure de système de transport urbain (e.g. système de transport intelligent multimodal) etc. Dans cette thèse, je présenterai un système embarqué dédié à la communication inter-véhicule particulièrement pour les applications sécuritaires de passagers et de conducteurs. Nos efforts de recherche et de développement sont centrés sur deux principaux objectifs : minimiser le temps de latence intra-noeud et le délai de communication inter-véhicule en prenant en compte le changement dynamique du VANET. De ce fait pour atteindre ces objectifs, des nouvelles approches (e.g. inter-couche ‘Cross-layering’) ont été explorées pour respecter les contraintes de ressource (QoS, mémoire, CPU et énergie de la communication inter-véhicule) d’un système embarqué à faible coût. Le système de communication embarqué proposé comporte deux composants logiciels principaux : un protocole de communication dénommé CIVIC (Communication Inter Véhicule Intelligente et Coopérative) et un système d’exploitation temps réel appelé HEROS (Hybrid Event-driven and Real-time multitasking Operating System). CIVIC est un protocole de communication géographique à faible consommation énergétique et à faible temps de latence (délai de communication). HEROS gère contextuellement l’ensemble du système (matériel et logiciel) en minimisant le temps de latence et la consommation des ressources (CPU et mémoire). En outre, le protocole de communication CIVIC est équipé d’un système de localisation LCD-GPS (Low Cost Differential GPS). Pour tester et valider les différentes techniques et théories, la plateforme matérielle LiveNode (LImos Versatile Embedded wireless sensor NODE) a été utilisée. En effet, la plateforme LiveNode permet de développer et de prototyper rapidement des applications dans différents domaines. Le protocole de communication CIVIC est basé sur la technique de ‘broadcast’ à un saut ; de ce fait il est indépendant de la spécificité du réseau. Pour les expérimentations, seule la norme d’IEEE 802.15.4 (ZigBee) a été choisie comme médium d’accès sans fil. Il est à noter que le médium d’accès sans fil ZigBee a été adopté comme le médium standard pour les réseaux de capteurs sans fil (RCSFs) et le standard 6LoWPAN ; car il est peu coûteux et peu gourmand en énergie. Bien que le protocole de communication à l’origine soit conçu pour répondre aux exigences de VANET, ses domaines d’application ne sont pas limités à VANET. Par exemple il a été utilisé dans différents projets tels que MOBI+ (système de transport urbain intelligent) et NeT-ADDED (projet européen FP6 : agriculture de précision). Les VANETs et les RCSFs sont les réseaux fortement dynamiques, mais les causes de changement topologique de réseau sont différentes : dans le réseau VANET, il est dû à la mobilité des véhicules, et dans le RCSF, il est dû aux pannes des noeuds sans fil. Il est à noter que le VANET et le RCSF sont généralement considérés comme un sous-ensemble du réseau MANET (réseau ad-hoc mobile). Cependant, ils sont réellement tout à fait différents du MANET classique, et leurs similitudes et différences seront expliquées en détail dans la thèse. La contribution principale de mes travaux est le protocole CIVIC, qui échange des messages en basant sur l’information géographique des noeuds (position). (...) / Each year in Europe, 1,300,000 vehicle accidents result in 1,700,000 personal injuries. The financial cost of vehicle accidents is evaluated at 160 billion Euros (approximately the same cost in the USA). VANET (Vehicular Ad-Hoc NETwork) is a key technology that can enable hazard alarming applications to reduce the accident number. In addition to improve the safety for drivers and passengers, VANET can contribute to many potential applications such as detecting and predicting traffic jams, auto-optimizing the traffic flow, and helping disabled passengers to access public transports.This thesis will present an embedded communication system dedicated to VANET especially for the safety-related applications. Our design mainly tries to achieve two requirements: as one can imagine, the embedded communication system for VANET requires extra effort to deal with the highly dynamic network topology caused by moving vehicles, thus to shorten the intra-node system latency and inter-node network delay is essential requirement for such embedded communication system. Besides, a fundamental requirement for any practical embedded system is resource-awareness. Although the embedded communication system on vehicles may gain better hardware supports, the characteristics of embedded hardware still have to cope with resource constraints in terms of QoS, memory, CPU and energy. The embedded communication system involves two major software components: a routing protocol called CIVIC (Communication Inter Véhicule Intelligente et Coopérative) and an embedded operating system called HEROS (Hybrid Event-driven and Real-time multitasking Operating System). The former is a quick reaction and low resource consumption geographic protocol for inter-vehicle message transmissions; and the latter controls the whole system and assures intra-node resource awareness. In addition, the system can use a localization software solution called LCD-GPS (Low Cost Differential GPS) to improve the accuracy of locations. The hardware platform is LiveNode (LImos Versatile Embedded wireless sensor NODE), which is a versatile wireless sensor node enabling to implement rapidly a prototype for different application domains. The communication system is based on the one-hop broadcast, thus it does not have a strict limitation on network specification. For the experiments only, the IEEE 802.15.4 standard is chosen as the underlying wireless access medium. The standard is well known as a low-power consumption standard requiring low-cost devices. Notice that the IEEE 802.15.4 standard is also the wireless access medium of 6LoWPAN. Although the embedded communication system is originally designed to meet the requirements of VANET, but its application domains are not limited to VANET. For example, another network which can use the embedded communication system is WSN (Wireless Sensor Network). CIVIC was used to implement different real-world projects such MOBI+ (intelligent urban transportation system) and EU-FP6 NeT-ADDED (precision agriculture). Both VANET and WSN are highly dynamic networks, but the causes of changing network topology are different: the former is because of the high-mobility feature of vehicles, and the latter is because of the fault of wireless sensors. Note that, although VANET and WSN are both commonly considered as the subset of MANET (Mobile Ad-hoc NETwork), they are actually quite different from the classical MANET, and the similarities and differences will be further explained in the thesis. The major contribution of my works relates to the CIVIC protocol, which routes messages based on the geographic information. The related works of the thesis will focus on the geographic routing techniques, problems and solutions, but other related techniques will also be addressed. Note that, although some related projects were investigated but their implementation and experiment aspects were not detailed. (...)