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.

In Intelligent Transportation Systems (ITS), disseminating warning messages in a timely and efficient way through wireless short-range communications can save many lives and reduce traffic congestion. A geographical broadcast protocol provides data delivery to specified geographical areas, using multi-hop communications if needed. Among the main challenges for such protocols are forwarder selection and the reduction of the number of hops required to reach and cover the destination area.  In this thesis we propose an efficient geographical broadcast protocol called Preferred and Contention Based Forwarding (PCBF) and evaluate it through simulations. PCBF uses a combination of contention-based forwarding and selecting preferred forwarders also found in other protocols like Emergency Message Dissemination for Vehicular Environments (EMDV). Since the preferred forwarder is allowed to immediately forward the packet (evading contention among other potential forwarders), this approach reduces end-to-end delays. Notable extensions of PCBF compared to EMDV are the use of direct negative acknowledgements in case of unnecessary rebroadcasts and the use of forwarders outside the target region.  Our simulation results show that the PCBF protocol outperforms selected other protocols in terms of end-to-end delay, re-broadcast overhead and reliability in both sparse and dense networks.