Relays in communication networks is a well-researched topic. Historically, relays were used in analog radio and television to extend the coverage. Using relays in wireless data networking applications is a more recent problem. In the early 2000s, relays were introduced for Micro-cellular and Wi-Fi deployments. Recently it has been considered for sensor networks and Vehicular Ad-hoc Networks (VANETs) applications. In this dissertation we present a novel approach to determine the optimal bounds for the Medium Access Control (MAC) throughput at the target receiver in a multi-hop multirate wireless data network. For a given relationship between the throughput and the distance, and a given distance between the access point and the target receiver, there is a minimum number of nodes that provides the maximum throughput to the target receiver. It is always desirable to optimize the deployment from various aspects. These aspects are application dependent and they range from energy conservation in sensor networks to throughput and coverage maximization in data networks. We apply this novel approach to vehicular ad-hoc network (VANET) scenarios. Using multi-hop relays, we show how to determine the optimum throughput for communciation between two vehicles. The optimal number of relays is chosen to maximize the throughput for point-to-point communication between a source and a destination as well as broadcast among all vehicles in the coverage area of the source. Additionally, in the physical layer, performance issues arise from the effects of interference and fading. The physical layer performance will in turn impact medium access control performance, effectively reducing the network throughput. We evaluate the ii performance of dense small cells for wireless local area networks (WLAN) and femto cells for data applications under the effects of interference and fading. We assume the network is fully saturated. We use the throughput-distance relationship to take into consideration the effects of interference, fading as well as the medium access control overheads. Using this model, we show that under certain conditions, the medium access control throughput for WLANs can outperform that of femto cells.

Antennas are essential components in any wireless communication system. To evaluate them is challenging, especially when new technologies are emerging. Future intelligent transport systems, where vehicular communications play an important role will cover important aspects such as traffic safety and traffic efficiency. These applications will be covered by technologies such as IEEE 802.11p and LTE. For these emerging technologies, traditional methods for measuring the vehicular antennas such as anechoic chamber measurements or expensive and time-consuming field measurements may not be enough or suitable. Thus a new method for evaluating the antennas performance is desirable. A method that includes the multipath environment to give an idea of the antenna performance in the whole system and at the same time be able to be applied at early stages of product development. This thesis aims to provide such method. The thesis is divided in two parts. The first part contains an overview and background of important concepts needed for development of methods for evaluation of vehicular antennas. In the second part, the papers that constitute the core of this work are appended. In Paper A, we evaluate the vehicle’s antenna performance using only simulations. We start by defining the multipath environment for vehicle-tovehicle and vehicle-to-infrastructure (V2X) communication. Then, the V2X environment is simulated using a multipath simulation tool to evaluate the vehicle’s antennas radiation patterns placed at different positions on the vehicle. This will result in the received power cumulative distribution functions (CDFs) for the voltage samples at the receiving antennas port. In Paper B, we present the design and evaluation of an antenna module for IEEE 802.11p and LTE technologies. The module is designed taking into consideration the available space and suitable placement on the vehicle. The proposed module is in accordance with the requirements for LTE and IEEE 802.11p technologies. This is validated with the analysis of the antenna efficiencies, S-parameters, radiation patterns, and diversity performance for the simulated and measured antenna module. Finally, Paper C presents a method for the evaluation of V2V antennas in a simulated measurement-based multipath environment. Here, a measurement campaign is performed to obtain the parameters (i.e., the angular received power spectrum) that define a realistic V2V multipath environment. These parameters are then introduced in a multipath simulation tool where the antennas radiation patterns are evaluated. Results are expressed in terms of received power CDFs. This method is validated by comparing the simulated and measured received power for two roof-top vehicle antennas.

Vehicle to Vehicle (V2V) communication provides a flexible and real-time information dissemination mechanism through various applications of Intelligent Transportation Systems (ITS). Achieving seamless connectivity through multi-hop vehicular communication with sparse network is a challenging issue. In this paper, we have studied this multi-hop vehicular connectivity in an urban scenario using GPS traces obtained from San Francisco Yellow cabs. Our current work describes a new algorithm for the analysis of topological properties like connectivity and partitions for any kind of vehicular or mobile computing environment. The novel approach uses bitwise manipulation of sparse matrix with an efficient storage technique for determining multi-hop connectivity. The computation mechanism can be further scaled to parallel processing environment. The main contribution of this research is threefold. First, developing an efficient algorithm to quantify multi-hop connectivity with the aid of bitwise manipulation of sparse matrix. Second, investigating the time varying nature of multi-hop vehicular connectivity and dynamic network partitioning of the topology. Third, deriving a mathematical model for calculating message propagation rate in an urban environment.

Recently, according to people's requirements for safe and congestion-free driving in the public transportation system, the intelligent transportation system (ITS) has been widely concerned. To achieve a safe and time-saving driving experience in ITS, various data sharing methods are proposed to provide traffic information for drivers to perceive their surrounding driving environment. However, the high dynamic characteristic of the vehicular network (VNET) results in a challenging environment for establishing stable communication among vehicles. To face this challenge, a Cellular network-assisted Reliable Traffic-Aware Routing protocol (CRTAR) is proposed in this thesis to provide support for vehicle’s data routing process in a heterogeneous vehicular-cellular network environment. In the method, city-wide traffic information, i.e., traffic density and data transmission density of the road segments, is introduced into vehicle's data routing process to assist the vehicle in selecting the optimal data transmission route to deliver data packets. To further improve the stability of inter-vehicle communication, the link lifetime between vehicles is also considered to select the next forwarder that can establish relatively robust communication. CRTAR takes advantage of the reliability and low-latency features of the communication technology in the cellular network and combines the cellular network with VNET to achieve real-time and reliable Vehicle-to-Infrastructure (V2I) communication. Meanwhile, it realizes the Vehicle-to-Vehicle (V2V) communication by the Dedicated Short Range Communication (DSRC) to mitigate the overload of backbone resources caused by using the cellular network. To be specific, in the method, vehicles can request city-wide traffic information via the cellular network from a cloud service that is connected to the remote data center located in the traffic management agency without latency. According to the real-time traffic information, the source vehicle can execute the data routing process with a global view of the system to calculate the data transmission route that has sufficient transmission resources to the target vehicle. The source vehicle then transmits data to the target via the vehicles in the calculated transmission route. During the forwarding process, vehicles prefer to forward the data packet to the next vehicle with a longer link lifetime. Furthermore, effective backup and recovery strategies are designed for route maintenance. The effectiveness of CRTAR is further verified by conducting simulation experiments.

The emerging concept of vehicle cloudification is a promising solution to deal with ever-growing computational and communication demands of connected vehicles. A key idea is to have connected vehicles in the vicinity form a cluster which is called vehicular micro cloud. Vehicles in this micro cloud collaborate with other cluster members over vehicle-to-vehicle (V2V) networks for collective data processing, shared data storage, collaborative sensing and communication services. A typical use case of vehicular micro cloud is creation of a regional distributed data storage service, where member vehicles of the cloud collaboratively keep data contents in their on-board data storage devices. This allows vehicles in and around the vehicular micro cloud to request the contents from the micro cloud member(s) over vehicle-to-vehicle networks, or even update the data on the spot. In this thesis, we will discuss the need for vehicular micro clouds, followed by the architecture, formation of the micro clouds, and feasibility of micro clouds. Furthermore, we will cover aspects of efficient data transmission between vehicles, how to increase the scalability and to make it time efficient and cost efficient on practical road conditions for moving vehicles by encouraging coordination between neighboring micro cloud to help transfer data .

Electric vehicles (EVs) have emerged to be the future of transportation as the world observes its rising demand and usage across continents. However, currently, one of the biggest bottlenecks of EVs is the battery. Small batteries limit the EVs driving range, while big batteries are expensive and not environmentally friendly. One potential solution to this challenge is the deployment of charging roads, i.e., dynamic wireless charging systems installed under the roads that enable EVs to be charged while driving. In this thesis, we establish a framework using stochastic geometry to study the performance of deploying charging roads in metropolitan cities. We first present the course of actions that a driver may take when driving from a random source to a random destination, and then analyze the distribution of the distance to the nearest charging road and the probability that the trip passes through at least one charging road. These probability distributions assist not only urban planners and policy makers in designing deployment plans of dynamic wireless charging systems, but also drivers and automobile manufacturers in choosing the best driving routes given the road conditions and level of energy of EVs.

Dans ces dernières années, les Systèmes de Transport Intelligents (STI) ont été considérés comme l'un des domaines de recherche les plus émergents en raison de leur rôle prometteur dans l'amélioration de la gestion du trafic et de la sécurité routière. Les applications coopératives de sécurité, étant les plus cruciales, ont gagné beaucoup d'intérêt. L'efficacité de ces applications dépend largement de l'échange efficace de deux principaux types d'informations. L'information de localisation périodique correspondant à l'information de localisation du voisinage et l'information événementielle qui est transmise en multi-sauts et générée lors de la détection d'une situation d'urgence. En raison de la caractéristique à grande échelle des STI, cette information fait l'objet du problème de congestion dans le réseau. L'objectif de cette thèse est d'assurer un contrôle fiable et robuste des informations de sécurité permettant de réduire la congestion du canal tout en tenant en compte des exigences des applications de sécurité. Nous examinons la diffusion de l'information événementielle en proposant une approche a multi-sauts qui a montré une amélioration de la réception de l'information. Cependant, cette approche reste très sensible à la charge de canal résultant de transmissions de l'information de localisation périodiques. D'autre part, la transmission efficace de l'information événementielle repose essentiellement sur la détection précise des événements de sécurité et en conséquence sur la précision de l'information de localisation. Ainsi, nous proposons un mécanisme de contrôle de l'information de localisation afin de fournir une meilleure précision et limiter la charge du canal. Les approches proposées dans cette thèse ont profondément étudié le compromis entre le respect des exigences des applications de sécurité et la gestion efficace de la congestion dans le réseau véhiculaire. / In the last decades, Intelligent Transportation Systems (ITS) have been considered as one of the most emerging research area due to their promising role in promoting traffic efficiency and enhancing road safety. ITS cooperative safety applications, being the most vital and critical, have gained a lot of attention. The effectiveness of these applications depends widely on the efficient exchange of two main types of information. The periodic awareness corresponding to the one-hop location information of surrounding environment and the multi-hop event-driven information generated at the detection of a safety situation. Due to the large scale characteristic of ITS, this information is expected to be subject to severe congestion which might impact its reliable reception. The goal of this thesis is to focus on the reliable and robust control of safety-related information by reducing the channel congestion and at the same time taking into account the requirements of safety applications. We address first the event-driven safety information. We proposed a multi-hop policy showed to improve the dissemination of the event-driven information. However, it remains strongly sensitive to the channel load resulting from periodic awareness transmissions. On the other hand, the effective transmission of event-driven information depends primarily on the accurate detection of safety events and accordingly on the accuracy of awareness. Thus, we provide an efficient awareness control mechanism in order to provide better accuracy and limit the channel congestion. The approaches proposed in this thesis have deeply investigated the trade-off between ensuring the requirements of cooperative safety and the efficient management of congestion in vehicular network.

No description available.

Vehicular communication systems rely on temporary anonymous identities, i.e. pseudonyms, in order to establish security and at the same time avoid the possibility of tracking vehicles. If a vehicle uses only one pseudonym, an adversary would be able to follow the vehicle by observing and linking messages, signed under that pseudonym. Therefore, the vehicles acquire a set of pseudonyms from the VPKI, i.e. infrastructure of the communication system, and switches pseudonym frequently. If a vehicle would be unable to acquire these pseudonyms, it would not be able to utilize the communication system without compromising its privacy. A vehicle is able to create its own pseudonyms using group signatures, i.e. the so-called Hybrid scheme. However, a pseudonym issued by the VPKI and a pseudonym created with a group signature would look different to an observer. If only one vehicle used pseudonyms created with group signature, it would easily be singled out and tracked. This thesis proposes a solution to this problem, but not the broader problem of linking messages by other means, e.g. the content of the message. In the solution, a vehicle is able to generate its own pseudonyms, using the Hybrid scheme, and make them unlinkable at the cost of computational overhead for itself and the vehicles around it, since group signatures are costly. The vehicle achieves this by aligning the lifetime of the pseudonym with other pseudonyms and asking neighboring vehicles to alternate randomly between using pseudonyms issued by the VPKI and pseudonyms created with group signatures. This alternation by neighboring vehicles decreases the linkability of pseudonyms created with group signature without increasing the linkability of pseudonyms created by the VPKI. This results in a trade off between reasonable computational overhead and acceptable linkability for pseudonyms. A short paper, presenting the scheme and results of this thesis, has been accepted to the IEEE Vehicular Networking Conference in Torino, Italy, 27-29 November, 2017 [1]. / Fordonskommunikation utnyttjar temporära identiteter, dvs. pseudonymer, för att etablera säkerhet och samtidigt undvika möjligheten att spåra fordon. Om ett fordon skulle använda endast ett pseudonym så skulle en observatör kunna följa fordonet genom att observera och länka meddelanden signerade under det pseudonymet. Varje fordon erhåller därför ett set pseudonymer från kommunikationssystemet och byter pseudonym regelbundet. Om ett fordon inte kan erhålla dessa pseudonymer från systemet, så skulle fordonet inte kunna utnyttja kommunikationssystemet utan att förkasta sin integritet. Ett fordon skulle kunna skapa sina egna pseudonymer genom att använda gruppsignaturer, dvs. det så kallade Hybrid scheme. Problemet är att ett pseudonym som är erhållet från kommunikationssystemet och ett pseudonym som är genererat med en gruppsignatur, ser olika ut för en observatör. Om endast ett fordon skulle använda pseudonymer med gruppsignaturer, så skulle det enkelt filtreras ut och spåras. Den här avhandlingen föreslår en lösning på detta problem, men inte till det större problemet att länka meddelanden på andra sätt, exempelvis använda informationen i själva meddelandet. I lösningen kan fordonetgenerera egna pseudonymer, genom att använda gruppsignaturer, dvs. Hybrid scheme, och göra dem olänkbara till priset av extra beräkningstid för sig själv och fordonen omkring sig, eftersom gruppsignaturer är kostsamma. Fordonet uppnår det genom att synkronisera pseudonymernas livslängd med de andra pseudonymerna och fråga fordonen i närheten om de kan slumpmässigt växla mellan att använda pseudonymer från systemet och pseudonymer som de skapat med gruppsignaturer. Om fordon i närheten växlar mellan pseudonymer från systemet och pseudonymer genererade med gruppsignaturer så minskar länkbarheten av pseudonymer baserade på gruppsignaturer utan att öka länkbarheten av pseudonymer från kommunikationssystemet. Det resulterar i en avvägning mellan beräkningstid och acceptabel länkbarhet av pseudonymer. Ett konferens papper, som presenterar protokollet och resultatet av denna avhandling, har blivit accepterat till IEEE Vehicular Networking Conference i Torino, Italien, 27-29 November 2017 [1].

In intelligent transportation systems, the cooperation between vehicles and the road side units is essential to bring these systems to fruition. Vehicular ad hoc networks (VANETs) are a promising technology to enable the communications among vehicles on one hand and between vehicles and road side units on the other hand. However, it is a challenging task to develop a reliable routing algorithm for VANETs due to the high mobility and the frequent changes of the network topology. Communication links are highly vulnerable to disconnection in VANETs; hence, the routing reliability of these ever-changing networks needs to be paid special attention. In this paper, we propose a new vehicular reliability model to facilitate the reliable routing in VANETs. The link reliability is defined as the probability that a direct communication link between two vehicles will stay continuously available over a specified time period. Furthermore, the link reliability value is accurately calculated using the location, direction and velocity information of vehicles along the road. We extend the well-known ad hoc on-demand distance vector (AODV) routing protocol to propose our reliable routing protocol AODV-R. Simulation results demonstrate that AODV-R outperforms significantly the AODV routing protocol in terms of better delivery ratio and less link failures while maintaining a reasonable routing control overhead.