Safety of a multi-vehicle system in mixed communication environments

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2007.Includes bibliographical references (leaves 131-138).Recent news events and statistics demonstrate the frequent occurrence of pile-up crashes on highways. A predominant reason for the occurrence of such crashes is that current vehicles (including those equipped with an Automatic Cruise Control system) do not provide the driver with advance information of events occurring far ahead of him/her. The use of inter-vehicular communication to provide advance warnings to enhance automotive safety is therefore being actively discussed in the research community. In this thesis, we investigate scenarios wherein only a subset of the vehicles in a multi-vehicle stream, are equipped with such advance warning capabilities. These vehicles (equipped with the capability to receive far-ahead information) are arbitrarily distributed among other unequipped vehicles that are capable of receiving only local, near-neighbor information. It is seen that there are conditions wherein even a partial equipment of the system can be beneficial (to both the equipped and the unequipped vehicles in a mixed vehicle stream). We demonstrate this through both simulations and a theoretical analysis. Towards this end, two distinct modeling approaches are adopted: microscopic and macroscopic.(cont.) The microscopic modeling approach uses ordinary differential equations to model each driver-vehicle unit and its interactions with its neighbors. A single-lane model is employed; and the problem is formulated as a collision avoidance problem. Sufficient conditions on the number of equipped vehicles, as well as their distributions in a mixed vehicle string are obtained; under these conditions, it is guaranteed that collisions do not occur. The macroscopic modeling approach, on the other hand, uses partial differential equations that govern the average behavior of groups of vehicles. In this approach, a multi-lane formulation is employed. This thesis examines the influence of partial equipment of the advance warning system on some of the wave effects that are known to exist in traffic flows, in particular, shocks and large negative velocity gradient waves that travel unattenuated or get amplified as they pass through the traffic. We examine the influence of the equipped vehicles in attenuating such waves. The resulting velocity gradients are parametrized as a function of the percentage of equipped vehicles. A prototype of an advance warning system was also developed and road tests were conducted to test the concept. These road tests have demonstrated the system's performance to be satisfactory, subject to good communication links, for the class of scenarios tested.by Animesh Chakravarthy.Ph.D

Connected Vehicle Technology: User and System Performance Characteristics

The emerging connected vehicle (CV) technology plays a promising role in providing more operable and safer transportation environments. Yet, many questions remain unanswered as to how various user and system characteristics of CV-enabled networks can shape the successful implementation of the technology to maximize the return on investment. This research attempts to capture the effect of multiple factors such as traffic density, market penetration, and transmission range on the communication stability and overall network performance by developing a new CONnectivity ROBustness (CONROB) model. The model was tested with data collected from microscopic simulation of a 195 sq-mile traffic network and showed a potential to capture the effect of such factors on the communication stability in CV environments. The information exchanged among CVs can also be used to estimate traffic conditions in real time by invoking the probe vehicle feature of CV technology. Since factors affecting the connectivity robustness also have an impact on the performance of traffic condition estimation models, a direct relationship between connectivity robustness and traffic condition estimation performance was established. Simulation results show that the CONROB model can be used as a tool to predict the accuracy of the estimated traffic conditions (e.g. travel times), as well as the reliability of such estimates, given specific system characteristics. The optimal deployment of road-side units (RSUs) is another important factor that affects the communication stability and the traffic conditions estimates and reliability. Thus, an optimization approach was developed to identify the optimal RSUs locations with the objective function of maximizing the connectivity robustness. Simulation results for the developed approach show that CONROB model can help identify the optimal RSUs locations. This shows the importance of CONROB model as a planning tool for CV environments. For the individual user performance characteristics, a preliminary driving simulator test bed for CV technology was developed and tested on thirty licensed drivers. Forward collision warning messages were delivered to drivers when predefined time-to-collision values take place. The findings show improved reaction times of drivers when receiving the warning messages which lend credence to the safety benefits of the CV technology

Reliable and efficient data dissemination schemein VANET: a review

Vehicular ad-hoc network (VANET), identified as a mobile ad hoc network MANETs with several added constraints. Basically, in VANETs, the network is established on the fly based on the availability of vehicles on roads and supporting infrastructures along the roads, such as base stations. Vehicles and road-side infrastructures are required to provide communication facilities, particularly when enough vehicles are not available on the roads for effective communication. VANETs are crucial for providing a wide range of safety and non-safety applications to road users. However, the specific fundamental problem in VANET is the challenge of creating effective communication between two fast-moving vehicles. Therefore, message routing is an issue for many safety and non-safety of VANETs applications. The challenge in designing a robust but reliable message dissemination technique is primarily due to the stringent QoS requirements of the VANETs safety applications. This paper investigated various methods and conducted literature on an idea to develop a model for efficient and reliable message dissemination routing techniques in VANET

On the achievable throughput of cooperative vehicular networks

© 2016 IEEE. Due to the time-varying channel conditions and dynamic topology of vehicular networks attributable to the high mobility of vehicles, data dissemination in vehicular networks, especially for content of large-size, is challenging. In this paper, we propose a cooperative communication strategy for vehicular networks suitable for dissemination of large-size content and investigate its achievable throughput. The proposed strategy exploits the cooperation of vehicle-to-infrastructure (V2I) communications, vehicle-to-vehicle (V2V) communications and the mobility of vehicles to facilitate the transmission. Detailed analysis is provided to characterize the data dissemination process using this strategy and a closed-form result is obtained on its achievable throughput, which reveals the relationship between major performance-impacting parameters such as distance between infrastructure, radio ranges of infrastructure and vehicles, transmission rates of V2I and V2V communications and vehicular density. Simulation and numerical results show that the proposed strategy significantly increases the throughput of vehicular networks even when the traffic density is low. The result also gives insight into the optimum deployment of vehicular network infrastructure to maximize throughput

Vehicle Networks: Statistical and Game Theoretic Approaches to Their Evaluation and Design

Vehicle ad hoc networks (VANETs) have become a popular topic in modern research. The main advantages of these networks include: improved security, traffic optimization, and infotainment. However, deploying such networks in practice requires extensive infrastructure. To estimate the network load, one needs to have information about the network, such as the number of clusters, cluster size, etc. Since VANETs are formed by vehicles that rapidly change their location, the network topology is constantly changing, making its analysis by deterministic methods impossible. Therefore, in this dissertation, we use probability theory methods to obtain probability distributions of such fundamental network properties, such as the number of clusters, cluster size, and the number of disconnected vehicles in the case in which the vehicles are located on a highway. In previous articles, some of these characteristics are obtained only in terms of average values, while the total distributions remained unknown. The distribution of the largest cluster size is an important characteristic of the network. It is derived in the dissertation for the first time. We also study the distribution of the number of clusters and the size of the average cluster in the case of a 2D map with an almost arbitrary road topology. To the best of our knowledge, these results are the first for such a general map case. Studying these properties raises a number of new questions about how these network properties change over time. We obtain distributions of the network characteristics, such as the duration of communication between vehicles, and the duration of cluster existence. We also derive the probability that a cluster exists between two time moments, as well as other network properties. The obtained distributions are new in the case of the Markov channel model. The results regarding the distribution of cluster lifetime and the probability of cluster existence between two fixed time moments are obtained in the literature for the first time. This dissertation also addresses the security aspect of VANET. We consider single and multichannel anti-jamming games in the case in which two communicating vehicles are being pursued by the jammer, which tries to disrupt the communication. The optimal strategies of the vehicles and the jammer are described as the Nash equilibrium of this game. We prove theorems that express Nash equilibrium through communication parameters. The considered model with quadratic power term is new as well as the results regarding the Nash equilibrium in the single and multichannel cases. We also first examine performance of such state-of-the-art machine learning algorithms as Dueling Q-learning and Double Q-learning, which by trial and error, successfully converge to the Nash equilibrium, deduced theoretically