Les travaux de cette thèse s'inscrivent tous dans la thématique " traitement du signal pour les réseaux de communications distribués ". Le réseau est dit distribué au sens de la décision. Dans ce cadre, le problème générique et important que nous avons approfondi est le suivant. Comment un terminal, qui a accès à plusieurs canaux de communications, doit-il répartir (de manière autonome) sa puissance d'émission entre ses canaux et l'adapter dans le temps en fonction de la variabilité des conditions de communications ? C'est le problème de l'allocation de ressources adaptative et distribuée. Nous avons développé 4 axes de travail qui ont tous conduits à des réponses originales à ce problème ; la forte corrélation entre ces axes est expliquée dans le manuscrit de thèse. Le premier axe a été l'alignement opportuniste d'interférence. Un des scénarios de référence est le cas où deux couples émetteur-récepteur communiquent en interférant (sur la même bande, en même temps, au même endroit, ...), où les 4 terminaux sont équipés de plusieurs antennes et où un émetteur est contraint de ne pas (ou peu) interférer sur l'autre (canal à interférence dit MIMO). Nous avons conçu une technique d'émission de signal multi-antennaire qui exploite l'observation-clé suivante et jamais exploitée auparavant: même lorsqu'un émetteur est égoïste au sens de ses performances individuelles, celui-ci laisse des ressources spatiales (dans le bon espace de signal et que nous avons identifié) vacantes pour l'autre émetteur. L'apport en performances en termes de débit par rapport aux meilleurs algorithmes existants a été quantifié grâce à la théorie des matrices aléatoires et des simulations Monte Carlo. Ces résultats sont particulièrement importants pour le scénario de la radio cognitive en milieu dense. Dans un second temps, nous avons supposé que tous les émetteurs d'un réseau sont libres d'utiliser leurs ressources de manière égoïste. Les ressources sont données ici par les canaux fréquentiels et la métrique individuelle de performance est le débit. Ce problème peut être modélisé par un jeu dont les joueurs sont les émetteurs. Une de nos contributions a été de montrer que ce jeu est un jeu de potentiel, ce qui est fondamental pour la convergence des algorithmes distribués et l'existence d'équilibre de Nash. De plus, nous avons montré l'existence d'un paradoxe de Braess : si l'espace d'optimisation d'un joueur grandit, les performances individuelles et globales peuvent s'en trouver réduites. Cette conclusion a une conséquence pratique immédiate : il peut y a voir intérêt de restreindre le nombre de canaux fréquentiels utilisables dans un réseau à interférence distribué. Dans le jeu précédent, nous avions constaté que les algorithmes distribués d'allocation de ressources (les algorithmes d'apprentissage par renforcement typiquement) demandent un grand nombre d'itérations pour converger vers un état stable tel qu'un équilibre de Nash. Nous avons ainsi proposé un nouveau concept de solution d'un jeu, à savoir l'équilibre de satisfaction ; les joueurs ne modifient pas leur action, même si celle-ci ne maximise pas leur gain, pourvu qu'un niveau minimal de performance soit atteint. Nous avons alors développé une méthodologie d'étude de cette solution (existence, unicité, convergence, ...). Une de nos contributions a aussi été de donner des algorithmes d'apprentissage qui convergent vers cette solution en un temps fini (et même court génériquement). De nombreux résultats numériques réalisés dans des scénarios imposés par Orange ont confirmé la pertinence de cette nouvelle approche. Le quatrième axe de travail a été la conception de nouveaux algorithmes d'apprentissage qui convergent vers des solutions de type équilibre logit, epsilon-équilibre ou équilibre de Nash. Notre apport a été de montrer comment modifier les algorithmes existants pour que ceux-ci évitent les phénomènes de cycles et convergent vers un équilibre présélectionné au départ de la dynamique. Une idée importante a été d'introduire une dynamique d'apprentissage de la fonction métrique de performances en couplage avec la dynamique principale qui régit l'évolution de la distribution de probabilité sur les actions possibles d'un joueur. Le cadre de ces travaux est parfaitement réaliste d'un point de vue informatif au niveau des terminaux en pratique. Il est montré une voie possible pour améliorer l'efficacité des points de convergence, ce qui constitue un problème encore ouvert dans ce domaine.

Wireless sensor networks offer the advantages of low cost, flexible measurement of phenomenon in a wide variety of applications, and easy deployment. Since sensor nodes are typically battery powered, energy efficiency is an important objective in designing sensor network algorithms. These algorithms are often application-specific, owing to the need to carefully optimize energy usage, and since deployments usually support a single or very few applications.<p> This thesis concerns applications in which the sensors monitor a continuous scalar field, such as temperature, and addresses the problem of determining the location of a contour line in this scalar field, in response to a query, and communicating this information to a designated sink node. An energy-efficient solution to this problem is proposed and evaluated. This solution includes new contour detection and query propagation algorithms, in-network-processing algorithms, and routing algorithms. Only a small fraction of network nodes may be adjacent to the desired contour line, and the contour detection and query propagation algorithms attempt to minimize processing and communication by the other network nodes. The in-network processing algorithms reduce communication volume through suppression, compression and aggregation techniques. Finally, the routing algorithms attempt to route the contour information to the sink as efficiently as possible, while meshing with the other algorithms. Simulation results show that the proposed algorithms yield significant improvements in data and message volumes compared to baseline models, while maintaining the integrity of the contour representation.

Wireless sensor networks offer the advantages of low cost, flexible measurement of phenomenon in a wide variety of applications, and easy deployment. Since sensor nodes are typically battery powered, energy efficiency is an important objective in designing sensor network algorithms. These algorithms are often application-specific, owing to the need to carefully optimize energy usage, and since deployments usually support a single or very few applications.<p> This thesis concerns applications in which the sensors monitor a continuous scalar field, such as temperature, and addresses the problem of determining the location of a contour line in this scalar field, in response to a query, and communicating this information to a designated sink node. An energy-efficient solution to this problem is proposed and evaluated. This solution includes new contour detection and query propagation algorithms, in-network-processing algorithms, and routing algorithms. Only a small fraction of network nodes may be adjacent to the desired contour line, and the contour detection and query propagation algorithms attempt to minimize processing and communication by the other network nodes. The in-network processing algorithms reduce communication volume through suppression, compression and aggregation techniques. Finally, the routing algorithms attempt to route the contour information to the sink as efficiently as possible, while meshing with the other algorithms. Simulation results show that the proposed algorithms yield significant improvements in data and message volumes compared to baseline models, while maintaining the integrity of the contour representation.

With the proliferation of laptops, smart phones, sensors and other small devices, our physical environment is increasingly networked. Applications in a variety of problem domains (e.g., intelligent construction, traffic monitoring, smart homes, etc.) need to efficiently and seamlessly execute on top of such emerging infrastructure. Such infrastructure tends to be unreliable, and the network configuration changes constantly (network hosts depart and reemerge frequently). Consequently, software has to be able to react to these changes continuously and change its behaviors accordingly. In this dissertation, I introduce PAQ (Persistent Adaptive Query), a middleware designed to ease the programming burden associated with writing such applications. PAQ employs a novel style of query-driven application development that allows programmers to build pervasive applications by employing persistent queries--queries that continuously monitor the environment. The dissertation discusses the design and implementation of a new middleware model that allows programmers to write high level specifications abstracting away several tedious implementation details. PAQ employs both novel protocols that automatically tag the quality of information obtained from the network and statistical techniques to post-process and smooth the data. The goal of this research is to ease the software engineering challenges encountered during the construction and deployment of several applications in emerging pervasive computing environments thorough the use of a query-driven application development paradigm. / text

Establishing peer-to-peer (P2P) file sharing for mobile ad hoc networks (MANET) requires the construction of a search algorithm for transmitting queries and search results as well as the development of a transfer protocol for downloading files matching a query. In this paper, we present a special-purpose system for searching and file transfer tailored to both the characteristics of MANET and the requirements of peer-to-peer file sharing. Our approach is based on an application layer overlay network. As innovative feature, overlay routes are set up on demand by the search algorithm, closely matching network topology and transparently aggregating redundant transfer paths on a per-file basis. The transfer protocol guarantees low transmission overhead and a high fraction of successful downloads by utilizing overlay routes. In a detailed ns-2 simulation study, we show that both the search algorithm and the transfer protocol outperform off-the-shelf approaches based on a P2P file sharing system for the wireline Internet, TCP and a MANET routing protocol.

This thesis provides three main contributions with respect to the Dynamic Channel and Power Assignment (DCPA) problem. DCPA refers to the allocation of transmit power and frequency channels to links in a cognitive dynamic spectrum network so as to maximize the total number of feasible links while minimizing the aggregate transmit power. In order to provide a method to compare related, yet disparate, work, the first contribution of this thesis is a unifying optimization formulation to describe the DCPA problem. This optimization problem is based on maximizing the number of feasible links and minimizing transmit power of a set of communications links in a given communications network. Using this optimization formulation, this thesis develops its second contribution: a evaluation method for comparing DCPA algorithms. The evaluation method is applied to five DPCA algorithms representative of the DCPA literature . These five algorithms are selected to illustrate the tradeoffs between control modes (centralized versus distributed) and channel/power assignment techniques. Initial algorithm comparisons are done by analyzing channel and power assignment techniques and algorithmic complexity of five different DCPA algorithms. Through simulations, algorithm performance is evaluated by the metrics of feasibility ratio and average power per link. Results show that the centralized algorithm Minimum Power Increase Assignment (MPIA) has the overall best feasibility ratio and the lowest average power per link of the five algorithms we investigated. Through assignment by the least change in transmit power, MPIA minimizes interference and increases the number of feasible links. However, implementation of this algorithm requires calculating the inverse of near singular matrices, which could lead to inaccurate results. The third contribution of this thesis is a proposed distributed channel assignment algorithm, Least Interfering Channel and Iterative Power Assignment (LICIPA). This distributed algorithm has the best feasibility ratio and lowest average power per link of the distributed algorithms. In some cases, LICIPA achieves 90% of the feasibility ratio of MPIA, while having lower complexity and overall lower average run time. / Master of Science

The applications of ad hoc wireless networks envisaged in this thesis are those related to issues of disaster management, rehabilitation, security and defense. The circumstances in such situations warrants the deployment of a quick ad hoc network that is simple and uses minimum resoures to get started. The communication within the network has to be reliable and it has to be simple so that it can be deployed in extremely compex topography and other climatic conditions. Since large batteries cannot be assumed to be at our disposal for the sake of communication at all the times, energy conservation by way of energy efficient schemes is a paramount issue. Ad hoc wireless networks are broadcast networks by nature. For all the communications, transmissions by the nodes are broadcast into the air. A networkwide broadcast is distinguished from this. When a node wants its data to reach all the other nodes in the network then it initiates a networkwide broadcast. There may be nodes in the network that are not directly reachable by the node that wants to do a networkwide broadcast. Networkwide broadcast is used by ad hoc wireless networks for routing protocols, updating of network status information, network organization and multicasting. Most importantly, the applications envisaged out of this thesis need all their data communication as networkwide broadcast alone. In an ad hoc wireless network, a networkwide broadcast is usually effected by the flooding mechanism, which is inherently inefficient, since all the nodes in the network have to transmit the same information. It is possible to exploit the topology of the network in such a way, that only a few of the nodes need to transmit the information to complete a networkwide broadcast. The thesis deals with a new scheme for a networkwide broadcast implemented in the media access control (MAC) layer of an ad hoc wireless network. The new scheme is developed by extending the concept of handshaking signals used in unicast, to the networkwide broadcast scenario. In the case of unicast, where there is an intended recipient, handshaking is done for reliability and happens through the RTS and CTS packets. This idea is extended to suit the networkwide broadcast scenario and the consequences are discussed in detail in the thesis. Intuitively, adding more packets for handshaking increases the number of bytes transmitted. But the results obtained are interesting, since the network transmits fewer bytes per networkwide broadcast, on an average, with the newly proposed scheme. A comparison is done with the implementation of simple flooding following the IEEE 802.11 standard. These results have been demonstrated by simulations. The average improvement is nearly 2.5 times reduction in the number of bytes transmitted per networkwide broadcast. The performance of a networkwide broadcast in an ad hoc wireless network is usually affected badly by losses due to transmssion error in the medium. In a medium with errors, persistence improves reliability. This reliability helps in bringing robustness. The advantage of the proposed scheme is that it uses the idea of persistence to ensure the networkwide broadcast reachabilityto be almost independent of transmission error rate. The MAC layer ensures that the broadcast packet reaches each and every node that is connected to the node that initiates the etworkwide broadcast. The effects of collision are also overcome. Our simulations establish that the scheme works correctly, and gives good performance.

Each day, Humanity loses thousands of persons on roads when they were traveling to work, to study or even to distract. The financial cost of these injuries is also terrifying: Some statistics evaluate the financial cost of vehicle accidents at 160 billion Euro in Europe each year. These alarming figures have driven researchers, automotive companies and public governments to improve the safety of our transportation systems and communication technologies aiming at offering safer roads and smooth driving to human beings. In this context, Vehicular Adhoc Networks, where vehicles are able to communicate with each others and with existent road side units, emerge as a promising wireless technology able to enhance the vision of drivers and offer larger telematic horizon. VANETs promising applications are not only restricted to road safety but span from vehicle trafficoptimization like flow congestion control to commercial applications like file sharing and internet access. Safety applications require that their alert information is propagated to the concerned vehicles (located in the hazardous zone) with little delay and high reliability. For these reasons, this category of applications is considered as delay sensitive and broadcast-oriented nature. While classical blind flooding is rapid, its major drawback is its huge bandwidth utilization. In this thesis, we are interested on enhancing vehicular communications under different scenarios and optimizations: First, We focus on deriving a new solution (EBDR) to disseminate alert messages among moving vehicles while maintaining it efficient and rapid. Our proposal is based on directional antennas to broadcast messages and a route guidance algorithm to choose the best path for the packets. Findings confirmed the efficiency of our approach in terms of probability of success and end-to-end delays. Moreover, in spite of the broadcast nature of the proposed technique, all transmissions stop very soon after the arrival of a packet to its destination representing a strong feature in the conception of EBDR. Second, we propose a novel mathematical framework to evaluate the performance of EBDR analytically. Although most of the proposed techniques present in literature use experimental or simulation tools to defend their performance, we rely here on mathematical models to confirm our achieved results. Our proposed framework allows to derive meaningful performance metrics including the probability of transmission success and the required number of hops to reach thefinal destination. Third, we refine our proposed broadcast-based routing EBDR to provide more efficient broadcasting by adjusting the transmission range of each vehicle based on its distance to the destination and the local node density. This mechanism allows better minimization of interferences and bandwidth's saving. Furthermore, an analytical model is derived to calculate thetransmission area in the case of a simplified node distribution. Finally, we are interested on data collection mechanisms as they make inter-vehicle communications more efficient and reliable and minimize the bandwidth utilization. Our technique uses Q-learning to collect data among moving vehicles in VANETs. The aim behind using the learning technique is to make the collecting operation more reactive to nodes mobility and topology changes. For the simulation part, we compare it to a non-learning version to study the effect of the learning technique. Findings show that our technique far outperforms other propositions and achieves a good trade off between delay and collection ratio. In conclusion, we believe that the different contributions presented in this Thesis will improve the efficiency of inter-vehicle communications in both dissemination and data collection directions. In addition, our mathematical contributions will enrich the literature in terms of constructing suitable models to evaluate broadcasting techniques in urban zones

Network management plays a vital role to keep a network and its application work e ciently. The network management in MANETs is a crucial and the challenging task, as these networks are characterized by dynamic environment and the scarcity of resources. There are various existing approaches for network management in MANETs. The Ad hoc Network Management Protocol (ANMP) has been one of the rst e orts and introduced an SNMP-based solution for MANETs. An alternative SNMP-based solu-tion is proposed by GUERRILLA Management Architecture (GMA). Due to self-organizing characteristic feature of MANETs, the management task has to be distributed. Policy-based network management relatively o ers this feature, by executing and applying policies pre-viously de ned by network manager. Otherwise, the complexity of realization and control becomes di cult Most of the works address the current status of the MANET to take the network man-agement decisions. Currently, MANETs addresses the dynamic and intelligent decisions by considering the present situation and all related history information of nodes into consid-eration. In this connection we have proposed a network management system using agents (NMSA) for MANETs, resolving major issues like, node monitoring, location management, resource management and QoS management. Solutions to these issues are discussed as inde-pendent protocols, and are nally combined into a single network management system, i.e., NMSA. Agents are autonomous, problem-solving computational entities capable of performing e ective operation in dynamic environments. Agents have cooperation, intelligence, and mobility characteristics as advantages. The agent platforms provide the di erent services to agents, like execution, mobility, communication, security, tracking, persistence and directory etc. The platform execution environment allows the agents to run, and mobility service allows them to travel among the di erent execution environments. The entire management task will be delegated to agents, which then executes the management logic in a distributed and autonomous fashion. In our work we used the static and mobile agents to nd some solutions to the management issues in a MANET. We have proposed a node monitoring protocol for MANETs, which uses both static agent (SA) and mobile agents (MA), to monitor the nodes status in the network. It monitors the gradational energy loss, bu er, bandwidth, and the mobility of nodes running with low to high load of mobile applications. Protocol assumes the MANET is divided into zones and sectors. The functioning of the protocol is divided into two segments, The NMP main segment, which runs at the chosen resource rich node (RRN) at the center of a MANET, makes use of SA which resides at same RRN, and the NMP subsegment which runs in the migrated MAs at the other nodes. Initially SA creates MAs and dispatches one MA to each zone, in order to monitor health conditions and mobility of nodes of the network. MAs carrying NMP subsegment migrates into the sector of a respective zone, and monitors the resources such as bandwidth, bu er, energy level and mobility of nodes. After collecting the nodes information and before moving to next sector they transfer collected information to SA respectively. SA in turn coordinates with other modules to analyze the nodes status information. We have validated the protocol by performing the conformance testing of the proposed node monitoring protocol (NMP) for MANETs. We used SDL to obtain MSCs, that repre-sents the scenario descriptions by sequence diagrams, which in turn generate test cases and test sequences. Then TTCN-3 is used to execute the test cases with respect to generated test sequences to know the conformance of protocol against the given speci cation. We have proposed a location management protocol for locating the nodes of a MANET, to maintain uninterrupted high-quality service for distributed applications by intelligently anticipating the change of location of its nodes by chosen neighborhood nodes. The LMP main segment of the protocol, which runs at the chosen RRN located at the center of a MANET, uses SA to coordinate with other modules and MA to predict the nodes with abrupt movement, and does the replacement with the chosen nodes nearby which have less mobility. We have proposed a resource management protocol for MANETs, The protocol makes use of SA and MA for fair allocation of resources among the nodes of a MANET. The RMP main segment of the protocol, which runs at the chosen RRN located at the center of a MANET, uses SA to coordinate with other modules and MA to allocate the resources among the nodes running di erent applications based on priority. The protocol does the distribution and parallelism of message propagation (mobile agent with information) in an e cient way in order to minimize the number of message passing with reduction in usage of network resources and improving the scalability of the network. We have proposed a QoS management protocol for MANETs, The QMP main segment of the protocol, which runs at the chosen RRN located at the center of a MANET, uses SA to coordinate with other modules and MA to allocate the resources among the nodes running di erent applications based on priority over QoS. Later, to reallocate the resources among the priority applications based on negotiation and renegotiation for varying QoS requirements. The performance testing of the protocol is carried out using TTCN-3. The generated test cases for the de ned QoS requirements are executed with TTCN-3, for testing of the associated QoS parameters, which leads to performance testing of proposed QoS management protocol for MANETs. We have combined the developed independent protocols for node monitoring, location management, resource management, and QoS management, into one single network management system called Network Management System using Agents (NMSA) for MANETs and tested in di erent environments. We have implemented NMSA on Java Agent development environment (JADE) Platform. Our developed network management system is a distributed system. It is basically divided into two parts, the Network Management Main Segment and other is Network Management Subsegment. A resource rich node (RRN) which is chosen at the center of a MANET where the Main segment of NMSA is located, and it controls the management activities. The other mobile nodes in the network will run MA which has the subsegments of NMSA. The network management system, i.e., the developed NMSA, has Network manage-ment main (NMSA main), Zones and sector segregation scheme, NMP, LMP, RMP, QMP main segments at the RRN along with SA deployed. The migrated MA at mobile node has subsegments of NMP, LMP, RMP, and QMP respectively. NMSA uses two databases, namely, Zones and sectors database and Node history database. Implementation of the proposed work is carried out in a con ned environment with, JDK and JADE installed on network nodes. The launched platform will have AMS and DF automatically generated along with MTP for exchange of message over the channel. Since only one JVM, which is installed, will executes on many hosts in order to provide the containers for agents on those hosts. It is the environment which o ered, for execution of agents. Many agents can be executed in parallel. The main container, is the one which has AMS and DF, and RMI registry are part of JADE environment which o ers complete run time environment for execution of agents. The distribution of the platform on many containers of nodes is shown in Fig. 1. The NMSA is based on Linux platform which provides distributed environment, and the container of JADE could run on various platforms. JAVA is the language used for code development. A middle layer, i.e., JDBC (java database connection) with SQL provides connectivity to the database and the application. The results of experiments suggest that the proposed protocols are e ective and will bring, dynamism and adaptiveness to the applied system and also reduction in terms network overhead (less bandwidth consumption) and response time.

Chaque jour, l'humanité perd des milliers de personnes sur les routes pendant qu'ils se rendaient à travailler, à étudier ou même à se distraire. Ce nombre alarmant s'accumule avec le coût financier terrifiant de ces décès: Certaines statistiques évaluent le coût à 160 milliards d'euros par an en Europe. Dans ce contexte, les réseaux véhiculaires (VANETs) émergent comme une technologie sans fil prometteuse capable d'améliorer la vision des conducteurs et ainsi offrir un horizon télématique plus vaste. Les applications de sécurité routière exigent que le message d'alerte soit propagé de proche en proche par les véhicules jusqu'à arriver à la zone concernée par l'alerte tout en respectant les délais minimaux exigés par ce type d'applications et la grande fiabilité des transmissions. Dans cette thèse, nous nous intéressons à l'amélioration de l'efficacité des communications inter-véhiculaires sous différents scénarios: tout d'abord, nous nous concentrons sur le développement d'une nouvelle solution, appelée EBDR, pour disséminer les informations d'alertes dans un réseau VANET tout en assurant des courts délais de bout en bout et une efficacité pour les transmissions. Notre proposition est basée sur des transmissions dirigées effectuées à l'aide des antennes directionnelles pour la diffusion des messages et un algorithme de guidage d'itinéraire afin de choisir le meilleur chemin pour le paquet. En dépit de son fonctionnement en diffusion, les transmissions de notre technique s'arrêtent très rapidement après l'arrivée du paquet à la destination finale ce qui représente une caractéristique fondamentale dans la conception d’EBDR. Deuxièmement, nous proposons un framework mathématique ayant pour objectif l'évaluation des performances d’EBDR analytiquement. Nos modèles analytiques permettent de dériver des métriques de performances significatives à savoir la probabilité de succès et le nombre de sauts requis pour atteindre la destination finale. En outre, nous proposons une amélioration de notre protocole EBDR dans le but de fournir une diffusion plus efficace. Pour cela, nous nous basons sur l'ajustement de la puissance de transmission de chaque véhicule en fonction de la distance qui le sépare de la destination et la densité locale des nœuds. Ce mécanisme de contrôle de congestion permet de mieux minimiser les interférences et économiser de la bande passante. En plus, un modèle mathématique a été élaboré pour calculer la surface de la zone de transmission dans le cas d'une distribution uniforme des nœuds. Finalement, nous nous sommes intéressés aux mécanismes de collecte de données dans les réseaux véhiculaires. Notre approche est basée sur l'utilisation du principe du Q-learning pour la collecte des données des véhicules en mouvement. L'objectif de l'utilisation de ce mécanisme d'apprentissage est de rendre l'opération de collecte mieux adaptée à la mobilité des nœuds et le changement rapide de la topologie du réseau. Notre technique a été comparée à des méthodes n'utilisant pas du "learning", afin d'étudier l'effet du mécanisme d'apprentissage. Les résultats ont montré que notre approche dépasse largement les autres propositions en terme de performances et réalise un bon compromis entre le taux de collecte et les délais de bout en bout. Pour conclure, nous pensons que nos différentes contributions présentées tout le long de cette thèse permettront d'améliorer l'efficacité des communications sans fil inter-véhiculaires dans les deux directions de recherches ciblées par cette thèse à savoir : la dissémination des messages et la collecte des données. En outre, nos contributions de modélisation mathématique enrichiront la littérature en termes de modèles analytiques capables d'évaluer les techniques de transmission des données dans un réseau véhiculaire / Each day, Humanity loses thousands of persons on roads when they were traveling to work, to study or even to distract. The financial cost of these injuries is also terrifying: Some statistics evaluate the financial cost of vehicle accidents at 160 billion Euro in Europe each year. These alarming figures have driven researchers, automotive companies and public governments to improve the safety of our transportation systems and communication technologies aiming at offering safer roads and smooth driving to human beings. In this context, Vehicular Adhoc Networks, where vehicles are able to communicate with each others and with existent road side units, emerge as a promising wireless technology able to enhance the vision of drivers and offer larger telematic horizon. VANETs promising applications are not only restricted to road safety but span from vehicle trafficoptimization like flow congestion control to commercial applications like file sharing and internet access. Safety applications require that their alert information is propagated to the concerned vehicles (located in the hazardous zone) with little delay and high reliability. For these reasons, this category of applications is considered as delay sensitive and broadcast-oriented nature. While classical blind flooding is rapid, its major drawback is its huge bandwidth utilization. In this thesis, we are interested on enhancing vehicular communications under different scenarios and optimizations: First, We focus on deriving a new solution (EBDR) to disseminate alert messages among moving vehicles while maintaining it efficient and rapid. Our proposal is based on directional antennas to broadcast messages and a route guidance algorithm to choose the best path for the packets. Findings confirmed the efficiency of our approach in terms of probability of success and end-to-end delays. Moreover, in spite of the broadcast nature of the proposed technique, all transmissions stop very soon after the arrival of a packet to its destination representing a strong feature in the conception of EBDR. Second, we propose a novel mathematical framework to evaluate the performance of EBDR analytically. Although most of the proposed techniques present in literature use experimental or simulation tools to defend their performance, we rely here on mathematical models to confirm our achieved results. Our proposed framework allows to derive meaningful performance metrics including the probability of transmission success and the required number of hops to reach thefinal destination. Third, we refine our proposed broadcast-based routing EBDR to provide more efficient broadcasting by adjusting the transmission range of each vehicle based on its distance to the destination and the local node density. This mechanism allows better minimization of interferences and bandwidth's saving. Furthermore, an analytical model is derived to calculate thetransmission area in the case of a simplified node distribution. Finally, we are interested on data collection mechanisms as they make inter-vehicle communications more efficient and reliable and minimize the bandwidth utilization. Our technique uses Q-learning to collect data among moving vehicles in VANETs. The aim behind using the learning technique is to make the collecting operation more reactive to nodes mobility and topology changes. For the simulation part, we compare it to a non-learning version to study the effect of the learning technique. Findings show that our technique far outperforms other propositions and achieves a good trade off between delay and collection ratio. In conclusion, we believe that the different contributions presented in this Thesis will improve the efficiency of inter-vehicle communications in both dissemination and data collection directions. In addition, our mathematical contributions will enrich the literature in terms of constructing suitable models to evaluate broadcasting techniques in urban zones