Optimized Spatial CSMA for VANETs: A Comparative Study using a Simple Stochastic Model and Simulation Results

International audienceThe high densities of network nodes has made spatial reuse an essential characteristic of modern wireless networks. In this paper, we evaluate the maximum throughput of Carrier Sense Multiple Access (CSMA) for Vehicular Ad-hoc Networks (VANETs) when spatial reuse is taken into account. We begin our study by extending a simple stochastic model in order to fit a VANET pattern and to obtain the spatial density of throughput in terms of the main network parameters. This model uses a Matern selection process with a random pattern of nodes distributed as a Poisson Point Process (PPP). Each node of the process receives a random mark and the nodes that have the smallest mark in their neighborhood are elected for transmission. We study both 1D and 2D network cases with an SIR (Signal over Interference Ratio) model. In order to verify the correctness of the model, extensive simulations are carried out using two simulation platforms: the network simulator, ns-3, and a simulator which is dedicated to CSMA systems. Fairly good matching between the results of the model and those obtained from simulators are observed, confirming the reliability of the theoretical model. Although the results did not perfectly match due to the number of assumptions made for the model, the results obtained nonetheless show the potential for a significant improvement in the overall throughput for VANETs and similar distributed networks

Comparison of Spatial Aloha and CSMA using Simple Stochastic Geometry Models for 1D and 2D Networks

International audience—Spatial throughput (i.e. throughput with spatial reuse) is important with new types of networks such as vehicular, sensor and military networks. The aim of this study is to compute the spatial throughput of Aloha and CSMA using tools for stochastic geometry. Our network nodes will be modeled as elements of a Poisson Point Process (PPP) of a one-or two-dimensional space. Spatial Aloha can be modeled easily, the transmitting nodes are just selected with a given transmission probability. In spatial CSMA the nodes with the smallest back-off counter in their neighborhood will be selected to transmit and thus we can use random marks to perform the selection. We use the two models we have built to compare the spatial density of successful transmissions of CSMA and Aloha. To carry out a fair comparison, we will optimize both schemes by adjusting their parameters. For spatial Aloha, we can adapt the transmission probability, whereas for spatial CSMA we have to find the suitable carrier sense threshold. The results obtained show that CSMA, when optimized, outperforms Aloha for nearly all the parameters of the network model values and we evaluate the gain of CSMA over Aloha. We also find interesting results concerning the effect of the model parameters on the performance of both Aloha and CSMA. The closed formulas we have obtained provide immediate evaluation of performance, whereas simulations may take minutes to give their results. Even if Aloha and CSMA are old protocols, this comparison of spatial performance is new and provides interesting and useful results

Optimisation of spatial CSMA using a simple stochastic geometry model for 1D and 2D networks

International audienceIn modern wireless networks especially in Machine-to-Machine (M2M) systems and in the Internet of Things (IoT) there is a high densities of users and spatial reuse has become an absolute necessity for telecommunication entities. This paper studies the maximum throughput of Carrier Sense Multiple Access (CSMA) in scenarios with spatial reuse. Instead of running extensive simulation with complex tools which would be somewhat time consuming, we evaluate the spatial throughput of a CSMA network using a simple model which produces closed formulas and give nearly instantaneous values. This simple model allows us to optimize the network easily and study the influence of the main network parameters. The nodes will be deployed as a Poisson Point Process (PPP) of a one or two dimensional space. To model the effect of (CSMA), we give random marks to our nodes and to elect transmitting nodes in the PPP we choose those with the smallest marks in their neighborhood. To describe the signal propagation, we use a signal with power-law decay and we add a random Rayleigh fading. To decide whether or not a transmission is successful, we adopt the Signal-over-Interference Ratio (SIR) model in which a packet is correctly received if its transmission power divided by the interference power is above a capture threshold. We assume that each node in our PPP has a random receiver at a typical distance from the transmitter i.e. the average distance between a node and its closest neighbor. We also assume that all the network nodes always have a pending packet. With all these assumptions, we analytically study the density of throughput of successful transmissions and we show that it can be optimized with regard to the carrier-sense threshold

Analysis of broadcast strategies and network parameters in IEEE 802.11p VANETs using simple analytical models

International audience—This paper proposes and analyzes different broadcast strategies in IEEE 802.11p Vehicular Ad-hoc NETworks (VANETs). The first strategy is the default IEEE 802.11p strategy. Using a model derived from the Bianchi model, we provide the network performance in terms of throughput and success rate. The second strategy is to use an acknowledgment technique similar to the acknowledgment with point-to-point traffic. A node will send its broadcast packet as in the default case,but it requires an acknowledgment from a neighbor node. This node may be a random neighbor or may be selected according to precise rules. We analyze this second strategy in terms of throughput and success rate. Somewhat surprisingly, we show that this second strategy improves the delivery ratio of the transmitted packets but reduces the overall throughput. This means that if the CAM messages (Cooperative Awareness Messages) are broadcasted, the total number of packets actually delivered will be greater with the default strategy than with the improved strategy. We propose a third strategy which consists in using the default strategy for normal packets, but we add random redundant transmissions to ensure greater reliability for very important packets. We show that with this simple technique, not only do we obtain suitable reliability, but we also achieve larger global throughput than with the acknowledgment-oriented technique. Another contribution of this paper is to compute network performance in terms of throughput and success rate with respect to the network parameters and to analyze their impact on performances

WAVE Low Latency Video Streaming for Platooning Safety Real-Time Application

International audienceThe use of Wireless Access in Vehicular Environ- ments (WAVE) technology for exchanging information between vehicles can positively influence the drivers behavior towards safer driving by reducing road accidents and improving driving performance. These exchanged information are more relevant to safety applications if presented as a real-time and high quality video stream. In this paper, we demonstrate the low latency video streaming as a safety application for platoon and reverse parking scenarios. The use of streaming safety application provides an additional tool to the platoon drivers to see the road traffic conditions. It helps the driver to make safer decision and reduce the overtaken risks during a manual overtaking maneuver for instance (i.e platoon output)

Gestion des messages de sécurité dans les réseaux VANET.

Quality of Service (QoS) requirements for VANET applications vary depending on the nature and type of the application. Therefore, a communication protocol in VANETs must be able to meet various QoS requirements according to the type of traffic. In VANET, the transmission channel is shared by all the vehicles using the same radio frequency. A poor exploitation of the channel can therefore lead to collisions and wasted bandwidth. A MAC protocol must therefore be designed to share the channel between the different nodes in an efficient and fair way.In this thesis we present the following contributions:1- Analysis and improvement of diffusion in the IEEE 802.11 standard.2- Optimization of the CSMA technique for 1D and 2D networks.3- Design of an adaptive transmission algorithm that updates the Carrier Sense threshold to reach a target value.4- Study the gain obtained by the use of directional antennas for Aloha, non-slotted Aloha, and CSMA.Les exigences de Qualité de Service (QoS) des applications VANET varient selon la nature et le type de l’application. Par conséquent, un protocole de communication VANET doit pouvoir répondre aux diverses exigences de QoS selon le type du trafic. Dans VANET, le canal de transmission est partagé par tous les véhicules en utilisant une même fréquence radio. Une mauvaise exploitation du canal peut donc conduire à des collisions et peut aussi engendrer un gaspillage de la bande passante. Un protocole MAC doit être alors conçu pour partager le canal entre les différents noeuds d’une manière efficace et équitable.Dans cette thèse nous présentons les contributions suivantes :1- Analyse et amélioration de la diffusion dans la norme IEEE 802.11.2- Optimisation de la technique CSMA pour des réseaux 1D et 2D.3- Développement d’un algorithme CSMA de transmission adaptatif qui met à jour le taux de détection de la porteuse en fonction d’une valeur de référence.4- Étude du gain obtenu par l’utilisation d’antennes directionnelles pour Aloha, Aloha non-slotté, et CSMA

Handling Safety Messages in Vehicular Ad-HocNetworks (VANETs)

Les exigences de Qualité de Service (QoS) des applications VANET varient selon la nature et le type de l’application. Par conséquent, un protocole de communication VANET doit pouvoir répondre aux diverses exigences de QoS selon le type du trafic. Dans VANET, le canal de transmission est partagé par tous les véhicules en utilisant une même fréquence radio. Une mauvaise exploitation du canal peut donc conduire à des collisions et peut aussi engendrer un gaspillage de la bande passante. Un protocole MAC doit être alors conçu pour partager le canal entre les différents noeuds d’une manière efficace et équitable.Dans cette thèse nous présentons les contributions suivantes :1- Analyse et amélioration de la diffusion dans la norme IEEE 802.11.2- Optimisation de la technique CSMA pour des réseaux 1D et 2D.3- Développement d’un algorithme CSMA de transmission adaptatif qui met à jour le taux de détection de la porteuse en fonction d’une valeur de référence.4- Étude du gain obtenu par l’utilisation d’antennes directionnelles pour Aloha, Aloha non-slotté, et CSMA.Quality of Service (QoS) requirements for VANET applications vary depending on the nature and type of the application. Therefore, a communication protocol in VANETs must be able to meet various QoS requirements according to the type of traffic. In VANET, the transmission channel is shared by all the vehicles using the same radio frequency. A poor exploitation of the channel can therefore lead to collisions and wasted bandwidth. A MAC protocol must therefore be designed to share the channel between the different nodes in an efficient and fair way.In this thesis we present the following contributions:1- Analysis and improvement of diffusion in the IEEE 802.11 standard.2- Optimization of the CSMA technique for 1D and 2D networks.3- Design of an adaptive transmission algorithm that updates the Carrier Sense threshold to reach a target value.4- Study the gain obtained by the use of directional antennas for Aloha, non-slotted Aloha, and CSMA

Analysis of the IEEE 802.11 EDCF scheme for broadcast traffic: Application for VANETs

International audienceIn this paper we propose a model of the IEEE 802.11 Enhanced Distributed Coordination Function (EDCF) which can build different access priorities for different classes of traffic. These priorities are obtained using different inter frame spacings called Arbitration Inter Frame Spacings (AIFSs) to differentiate the access of different classes of traffic. When a node has a pending packet it must first wait for the channel to become idle for a given number A of mini-slots σ before starting to decrement its back-off; this interval of A mini-slots σ is called the AIFS. If the channel becomes busy before this back-off expires, then the node will have to to wait for another A mini-slots before starting to decrement its back-off again. The nodes can also use different back-off windows to further differentiate between different classes of traffic. The model we propose is much simpler than previous models [1], [2], [3] and handles the more general case of a Poisson arrival for the traffic. Moreover, the model presented here is designed for broadcast traffic whereas most models handle point-to-point IEEE 802.11 transmission. When we have two classes of traffic, the model leads to two coupled non-linear equations involving the transmission rates in each class of traffics. These equations can be easily solved using simple numerical methods. The model then allows the successful rate or the throughput for each class of traffic to be computed in a straightforward manner. Numerical examples derived from VANET scenarios show the direct and positive influence of the Arbitration Inter Frame Spacings on the performance of each class of traffic

Evaluating the Gain of Directional Antennas in Linear VANETs using Stochastic Geometry

International audienceMaximizing the throughput of point-to-point communication has been the crux of wireless networks. In IEEE 802.11 networks, the first and prominent wireless technology, the model of point-to-point communication is still applicable today: the transmissions are between the wireless nodes and the access point, which usually serves as a gateway to the Internet. But this model is not well suited to more recent wireless systems such as Wireless Sensor Networks (WSNs) and Vehicular Ad Hoc NETworks (VANETs). In such networks, a very significant part of communication is between one node and its neighbors and simultaneous transmissions or, in other words spatial reuse, is required to insure good performance. When we consider communication from one node to its neighbor,an important metric is the density of successful simultaneous transmissions. Several studies such as [1], [2] have shown how this density of transmissions can be improved in Aloha or in CSMA networks. The aim of this paper is to show that the use of directional antennas can greatly improve the performance of the network in our neighbor-to-neighbor communication model because interference is greatly reduced. The model we build here allows a quantitative study of the performance and the improvement obtained with directional antennas to be be achieved. The study of Aloha (slotted and non-slotted) is very easy to accomplish and leads to closed formulas for the density of successful transmissions. The study of CSMA is more complex. We use a Matern selection process to mimic the behavior of CSMA in a random pattern of nodes distributed as a Poisson Point Process (PPP): each node receives a random mark and the nodes that have the smallest mark in their neighborhood are elected for transmission. Previous studies, such as [2], show that in CSMA networks, the density of successful transmissions is greatly influenced by the carrier sense detection threshold, which is one of the main parameters of CSMA. In this study we will assume that the carrier sense detection threshold is optimized to obtain the best performance of the CSMA network and our evaluations are performed under this condition. Our analytical models and our computation show that using directional antennas can lead to an improvement of up to more than 100% in the density of throughput compared to the normal use of unidirectional antennas

A simple Stochastic Geometry Model to test a simple adaptive CSMA Protocol: Application for VANETs

International audienceIn wired networks, systems are usually optimized to offer the maximum throughput of point-to-point and generally well identified transmissions. In the first widespread wireless networks such as IEEE 802.11, the model of point-to-point communication still applies; the transmissions are between the wireless nodes and the access point, which usually serves as a gateway to the Internet. Yet this model is no longer valid with more recent wireless systems such as Wireless Sensor Networks (WSNs) and Vehicular Ad Hoc NETworks (VANETs). In such networks, communication is between one node and its neighbors and simultaneous transmissions or, in other words spatial reuse, is required to insure good performance. Thus performance is directly linked to the density of successful simultaneous transmissions. Another important remark concerning wireless networks, past and present, is that most of these communications systems use Carrier Sense Multiple Access (CSMA) techniques. Previous studies, such as [1], show that in CSMA networks, the density of successful transmissions is greatly influenced by the carrier sense detection threshold, which is one of the main parameters of CSMA. In this paper, we use a simple stochastic model for CSMA to experiment an adaptive scheme which tunes the carrier sense threshold to the density of network nodes. This model uses a Matern selection process with a random pattern of nodes distributed as a Poisson Point Process (PPP). Each node in the process receives a random mark and the nodes that have the smallest mark in their neighborhood are elected for transmission, mimicking the election process of CSMA. The analysis in this paper indicates that an adaptive technique can be based on the average waiting times of packets. Alternatively, this technique can also be based on the number of neighboring nodes