Yasser Toor

Rush hour traffic jams are a daily occurence in large cities all over the world. These traffic jams result in congested roadways and highly dense network topologies. VANET medium access mechanisms need to be very efficient in order to cope with such events. In this paper we analyze the suitability of HIPERLAN Type 1’s EY-NPMA medium access protocol for high density VANETs. We compare its performance with an IEEE 802.11 based system, in terms of delay, throughput and delivery ratio. Our simulations in NS-3 show that EY-NPMA is quite stable, provides satisfactory delay and throughput and maintains a high delivery ratio in medium to high load conditions. We conclude that it might be very suitable for traffic jam scenarios.

The aim of this paper is to study slotted and nonslotted Aloha medium access (MAC) scheme in Vehicular Adhoc NETworks (VANETs). To this regard, we consider a onedimensional, liner network, which is an appropriate assumption for VANETs and differs from two-dimensional, planar models usually assumed for general Mobile Ad-hoc NETworks (MANETs). More precisely, we use a linear version of the Poisson bipolar network model proposed in [2], in which the locations of signal emitting vehicles form a homogeneous Poisson point process on the line, and where the receivers are within a fixed distance form these emitters. We use the well-established signal-overinterference and noise ratio (SINR) capture model assuming power-law mean path-loss and independent Rayleigh fading. First, we consider a capture/outage scenario with fixed bit rate coding, where the SINR must above a given threshold for a successful packet reception. In this setting we obtain explicit formulas to calculate the probability ...

VANET applications can be classified into two categories: user applications and safety applications. Both of them must rely on efficient vehicular ad hoc routing protocols in order to deliver the information to the corresponding destination(s). Many possible VANET applications, e.g., accident avoidance or distributed traffic management applications, do not need explicit unicast data exchange, but locally aggregate and process the dada broadcast by other vehicles. One-to-many communications is of great importance for VANETs since vehicles are likely to exchange data by diffusion rather than in a unicast manner. Many broadcast techniques have already been proposed for MANETs, but classical MANET flooding techniques may not be suitable for VANETs and do not take advantage of the additional information available in vehicles. In this chapter we investigate various broadcast techniques that may be used in VANETs.

The European project COM2REACT aims at building a local cooperative traffic management system through a peer-to-peer application, the Virtual Sub-Center (VSC), based on vehicle-to-vehicle (V2V) communication. COM2REACT is an enhancement of the REACT system, which relies on a central server that gathers data from probe vehicles, aggregates and analyzes them by an integrated set of models, and generates both vehicle-specific recommendations and information for relevant authorities. This additional collaborative layer will increase the reactivity of the system and avoid an overload of communication and of the central server with information only relevant at a local level. The intention of this paper is to give the reader an overview of the new technologies developed to reach the ambitious goals of COM2REACT: V2V communication, VSC and local traffic applications. For the covering abstract see ITRD E140665.

Les reseaux vehiculaires (Vehicular Ad Hoc Networks ou VANETs) ont pris une grande importance au cours des dernieres annes car on espere qu'ils pourront sauver des vies sur nos routes et offrir egalement de nouvelles opportunites commerciales. Meme s'ils font l'objet d'intenses recherches et d'efforts de normalisation, plusieurs problemes restent encore poses pour la conception des protocoles et des applications. Ces problemes sont surtout dus aux caracteristiques particulieres de ces reseaux : grande mobilite, haute vitesse relative, topologie variable et faible bande passante utilisable. Les concepteurs de protocoles doivent etre conscients des exigences des applications pour les reseaux vehiculaires ainsi que des limitations imposees par la technologie de ces reseaux. Il existe deux grandes categories d'applications pour les reseaux vehiculaires. La premiere consiste en les applications de securite; celles-ci visent a garantir la securite immediate du cond...

ABSTRACT Vehicular ad hoc networks (VANETs) are an important example of mobile ad hoc networks (MANETs) because they can save lives by improving safety on our road networks. They are difficult to design however due their inherent characteristics e.g., quickly changing topology, node density and relative speeds of vehicles. These characteristics also make current wireless media access control (MAC) protocols unsuitable for use in VANETs without modifications. In this paper we study the performance of these protocols to see how they can be tuned to design a VANET with optimal network throughput. We do a simulation study of two popular MAC schemes (ALOHA and CSMA) in a linear VANET and analyze them in terms of density of progress of the transmissions under different attenuation and fading conditions. The results show how network performance deteriorates with changes in the conditions and how we can improve it by tuning the MAC protocols. The results presented in this paper can be useful for the design and optimal tuning of VANETs in varying network conditions (attenuation, fading and noise).

ABSTRACT In opportunistic routing the next relay is selected at each hop of each packet depending on the local pattern of simultaneous transmitters. The protocol considered in this paper assumes that at each hop, the optimal relay is chosen in a greedy way such that the packet receiver minimizes the remaining distance to the destination. The selection between potential relays is done using a logarithmic scale. This is a more efficient solution than the usually proposed solutions that use a linear scale. We evaluate the benefits of this protocol in the context of the point-to-point traffic in vehicular ad hoc networks (VANETs). We conduct this evaluation using extensive simulations with two widely used medium access techniques: slotted Aloha and CSMA. We show that even in one-dimensional scenarios, this protocol significantly outperforms conventional shortest path routing, offering shorter mean end-to-end packet delivery delay and smaller channel utilization.

In this paper, we study safety applications in Vehicular Ad hoc Networks (VANETs). More specifically we concentrate on emergency situations after a car crash in a platoon of vehicles which have wireless transmission capabilities. In order to avoid multiple collisions, vehicles should exchange emergency information as quickly as possible. To extend the area in which the emergency information is sent,

A Vehicular Ad hoc NETwork (VANET) is often formed by a large group of vehicles communicating with each other without the use of any infrastructure. A key challenge in such a scenario is to design an efficient broadcast strategy that quickly disseminates the packets in the VANET. While several protocols have been proposed, most of them are based on the

ABSTRACT Reliable delivery of emergency messages is critical for VANET safety applications. However shadowing in VANETs can cause these packets to be lost. In this paper we propose a reliable opportunistic broadcast protocol (R-OB-VAN) that overcomes this problem and maintains a high delivery ratio and low average delay. The second contribution of this work is to define a simple but realistic model of shadowing caused by large vehicles and study its effect on the surrounding vehicles traveling on a highway. The results of our simulations show that R-OB-VAN delivers the emergency messages both quickly and with a high degree of reliability.

ABSTRACT Rush hour traffic jams are a daily occurence in large cities all over the world. These traffic jams result in congested roadways and highly dense network topologies. VANET medium access mechanisms need to be very efficient in order to cope with such events. In this paper we analyze the suitability of HIPERLAN Type 1’s EY-NPMA medium access protocol for high density VANETs. We compare its performance with an IEEE 802.11 based system, in terms of delay, throughput and delivery ratio. Our simulations in NS-3 show that EY-NPMA is quite stable, provides satisfactory delay and throughput and maintains a high delivery ratio in medium to high load conditions. We conclude that it might be very suitable for traffic jam scenarios.

ABSTRACT VANET applications can be classified into two categories: user applications and safety applications. Both of them must rely on efficient vehicular ad hoc routing protocols in order to deliver the information to the corresponding destination(s). Many possible VANET applications, e.g., accident avoidance or distributed traffic management applications, do not need explicit unicast data exchange, but locally aggregate and process the dada broadcast by other vehicles. One-to-many communications is of great importance for VANETs since vehicles are likely to exchange data by diffusion rather than in a unicast manner. Many broadcast techniques have already been proposed for MANETs, but classical MANET flooding techniques may not be suitable for VANETs and do not take advantage of the additional information available in vehicles. In this chapter we investigate various broadcast techniques that may be used in VANETs.