Evaluation of Synchronous and Asynchronous Reactive Distributed Congestion Control Algorithms for the ITS G5 Vehicular Systems

The IEEE 802.11p is the technology dedicated to vehicular communications to support road safety, efficiency, and comfort applications. A large number of research activities have been carried out to study the characteristics of the IEEE 802.11p. The key weakness of the IEEE 802.11p is the channel congestion issue, where the wireless channel gets saturated when the road density increases. The European Telecommunications Standardization Institute (ETSI) is in the progress of studying the channel congestion problem and proposed so-called Reactive Distributed Congestion Control (DCC) algorithm as a solution to the congestion issue. In this report we investigate the impacts of the Reactive DCC mechanism in comparison to the conventional IEEE 802.11p with no congestion control. Our study shows that the Reactive DCC scheme creates oscillation on channel load that consequently degrades communication performance. The results reveal that the channel load oscillation is due to the fact that in the Reactive DCC, the individual CAM (Cooperative Awareness Message) controllers react to the channel congestion in a synchronized manner. To reduce the oscillation, in this report we propose a simple extension to Reactive DCC, Asynchronous Reactive DCC, in which the individual CAM controllers adopt randomized rate setting, which can significantly reduce the oscillation and improve the network performance

Study on Merging Control Supported by IEEE 802.11p Systems for Highway Environments

International audienceCooperative Adaptive Cruise Control (CACC) systems are intended to make driving safer and more efficient by utilizing information exchange between vehicles (V2V) and/or between vehicles and infrastructures (V2I). An important application of CACC is safe vehicle merging when vehicles join a main road, achieved by compiling information on the movement of individual main road vehicles. To support such road safety applications, the IEEE standardized the 802.11p amendment dedicated to V2V and V2I communications. This paper seek answers to the questions as to whether the IEEE 802.11p can support merging control and how the communications performance is translated into the CACC performance. We build an analytical model of the IEEE 802.11p medium access control (MAC) for transmissions of the ETSI-standardized Cooperative Awareness Messages (CAM) and Decentralized Environmental Notification Messages (DENM) to support merging control. We also developed a highway merging decision algorithm. Using computer simulations, packet delivery ratio (PDR), and packet inter-reception (PIR) time of IEEE 802.11p-based V2V and V2I communications and their impact on the CACC performance are investigated. Our study discloses several useful insights including that PIR and throughput provide a good indication of the CACC performance, while improving PDR does not necessarily enhance the CACC performance. Moreover, thanks to its ability to reliably provide information at constant time intervals, the V2I structure preferred over V2V as a support for CACC

A framework for IP and non-IP multicast services for vehicular networks

International audienceEnabling drivers to be connected to the Internet and/or Vehicular Ad-hoc networks, is one of the main challenges of the future networking. This enables drivers to benefit from the existing Internet services as well as emerging ITS applications based on IP or non-IP communications (e.g geonetworking). Many of ITS applications such as fleet management require multicast data delivery. Existing works on this subject tackle mainly the problems of IP multicasting inside the Internet or geocasting in VANETs. This paper presents a new framework that enables Internet-based multicast services on top of VANETs. We introduce a self-configuring multicast addressing scheme based on the geographic locations of the vehicles coupled with a simplified approach that locally manages the group membership to allow packet delivery from the Internet. Moreover, we propose an approach that selects the appropriate network-layer protocol for either geocasting or IP multicasting depending on the vehicles' context and the application requirements. Finally, we present the integration of the designed framework to the ITS reference architecture

Study on merging control supported by IEEE 802.11p systems for highway environments

International audienceCooperative Adaptive Cruise Control (CACC) systems are intended to make driving safer and more efficient by utilizing information exchange between vehicles (V2V) and/or between vehicles and infrastructures (V2I). An important application of CACC is safe vehicle merging when vehicles join a main road, achieved by compiling information on the movement of individual main road vehicles. To support such road safety applications, the IEEE standardized the 802.11p amendment dedicated to V2V and V2I communications. This paper seek answers to the questions as to whether the IEEE 802.11p can support merging control and how the communications performance is translated into the CACC performance. We build an analytical model of the IEEE 802.11p medium access control (MAC) for transmissions of the ETSI-standardized Cooperative Awareness Messages (CAM) and Decentralized Environmental Notification Messages (DENM) to support merging control. We also developed a highway merging decision algorithm. Using computer simulations, packet delivery ratio (PDR), and packet inter-reception (PIR) time of IEEE 802.11p-based V2V and V2I communications and their impact on the CACC performance are investigated. Our study discloses several useful insights including that PIR and throughput provide a good indication of the CACC performance, while improving PDR does not necessarily enhance the CACC performance. Moreover, thanks to its ability to reliably provide information at constant time intervals, the V2I structure preferred over V2V as a support for CACC

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

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

Beacon delivery over practical V2X channels

International audienceThe problem of modelling V2X system based on partial (RSSI) measurements of the wireless propagation channel is considered. The study shows that the dual slope linear model well approximates pathloss in the V2X systems. We also show that in addition to distance dependent pathloss, incorporation of fast fading as well as its frequency selectivity have significant effect on the overall performance of the system. Interference from simultaneous transmissions is estimated based on medium access control (MAC) and realistic road traffic models. Our simulation results show how car traffic parameters and MAC behavior provide direct impact on the effective communication range of the V2X system

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

Fusion of Perception and V2P Communication Systems for Safety of Vulnerable Road Users

International audienceWith cooperative intelligent transportation systems (C-ITS), vulnerable road users (VRU) safety can be enhanced by multiple means.On one hand, perception systems are based on embedded sensors to protect VRUs. However, such systems may fail due to the sensors' visibility conditions and imprecision. On the other hand, Vehicle-to-Pedestrian (V2P) communication can contribute to the VRU safety by allowing vehicles and pedestrians to exchange information. This solution is, however, largely affected by the reliability of the exchanged information, which most generally is the GPS data. Since perception and communication have complementary features, we can expect that a fusion between these two approaches can be a solution to the VRU safety. In this work, we propose a cooperative system that combines the outputs of communication and perception. After introducing theoretical models of both individual approaches, we develop a probabilistic association between perception and V2P communication information by means of multi-hypothesis tracking (MHT). Experimental studies are conducted to demonstrate the applicability of this approach in real-world environments. Our results show that the cooperative VRU protection system can benefit of the redundancy coming from the perception and communication technologies both in line-of-sight (LOS) and non-LOS (NLOS) conditions. We establish that the performances of this system are influenced by the classification performances of the perception system and by the accuracy of the GPS positioning transmitted by the communication system