電波環境マップによる事前情報を利用した 高信頼車車間通信

近年，自動車の高度化による自動走行システムに注目が集まっている．自動走行システムには，加速，操舵，制動を同時に自動車がドライバーのアシストをする高度運転支援や，加速，操舵，制動を全て自動車がコントロールする完全自動走行といったシステムがあるが，この技術は，交通事故の低減，交通渋滞の緩和，運転の快適性の向上といった効果が期待され，国内外での研究開発が盛んにおこなわれている．また自動運転システムへの応用を目指して，高度道路交通システム(ITS: Intelligent Transport Systems)の研究がすすめられている．ITSでは車車間通信（V2V:Vehicle-to-Vehicle）や路車間通信（V2I:Vehicle-to-Infrastructure）により，車両同士または路側器と車両間で逐次通信をすることが考えられている．しかし，車両が常に移動していることから，受信信号品質は，周辺構造物，地形，周辺の他車両台数，送信車両からの距離などに応じて複雑に変動する．そのため自動運転システムに寄与するような安定通信の実現に課題がある．この問題を解決するために，通信を行っている車両を観測ノードとみなし，パケット受信時の受信電力およびパケットの復調可否を取得し，その地点での無線環境情報として，位置情報と共にネットワーク上に設置するデータベースに集約することを考える．集約された情報はデータベースと連携した統計サーバで統計化処理を行い，位置情報と共にデータベースに蓄積し，車両からのリクエストに応じて，その周囲の無線環境として提供することで，通信を行おうとしている車両での事前情報を利用することで，目的車両間の通信の高信頼化を図る．この事前情報を利用することで，，通信を行うときに周辺環境を考慮した適切なパラメータの選択により通信の効率化を図る事が可能になる．事前情報を利用して変更する通信パラメ-タとして，中継車両，送信電力，変調方式を検討し特性の評価を行った．電気通信大学201

Optimal Content Downloading in Vehicular Networks

We consider a system where users aboard communication-enabled vehicles are interested in downloading different contents from Internet-based servers. This scenario captures many of the infotainment services that vehicular communication is envisioned to enable, including news reporting, navigation maps and software updating, or multimedia file downloading. In this paper, we outline the performance limits of such a vehicular content downloading system by modelling the downloading process as an optimization problem, and maximizing the overall system throughput. Our approach allows us to investigate the impact of different factors, such as the roadside infrastructure deployment, the vehicle-to-vehicle relaying, and the penetration rate of the communication technology, even in presence of large instances of the problem. Results highlight the existence of two operational regimes at different penetration rates and the importance of an efficient, yet 2-hop constrained, vehicle-to-vehicle relaying

Scaling Laws for Vehicular Networks

Equipping automobiles with wireless communications and networking capabilities is becoming the frontier in the evolution to the next generation intelligent transportation systems (ITS). By means of vehicle-to-vehicle (V2V) and vehicle-to-infrastructure (V2I) communications, information generated by the vehicle-borne computer, vehicle control system, on-board sensors, or roadside infrastructure, can be effectively disseminated among vehicles/infrastructure in proximity or to vehicles/infrastructure multiple hops away, known as vehicular networks (VANETs), to enhance the situational awareness of vehicles and provide motorist/passengers with an information-rich travel environment. Scaling law for throughput capacity and delay in wireless networks has been considered as one of the most fundamental issues, which characterizes the trend of throughput/delay behavior when the network size increases. The study of scaling laws can lead to a better understanding of intrinsic properties of wireless networks and theoretical guidance on network design and deployment. Moreover, the results could also be applied to predict network performance, especially for the large-scale vehicular networks. However, map-restricted mobility and spatio-temporal dynamics of vehicle density dramatically complicate scaling laws studies for VANETs. As an effort to lay a scientific foundation of vehicular networking, my thesis investigates capacity scaling laws for vehicular networks with and without infrastructure, respectively. Firstly, the thesis studies scaling law of throughput capacity and end-to-end delay for a social-proximity vehicular network, where each vehicle has a restricted mobility region around a specific social spot and services are delivered in a store-carry-and-forward paradigm. It has been shown that although the throughput and delay may degrade in a high vehicle density area, it is still possible to achieve almost constant scaling for per vehicle throughput and end-to-end delay. Secondly, in addition to pure ad hoc vehicular networks, the thesis derives the capacity scaling laws for networks with wireless infrastructure, where services are delivered uniformly from infrastructure to all vehicles in the network. The V2V communication is also required to relay the downlink traffic to the vehicles outside the coverage of infrastructure. Three kinds of infrastructures have been considered, i.e., cellular base stations, wireless mesh backbones (a network of mesh nodes, including one mesh gateway), and roadside access points. The downlink capacity scaling is derived for each kind of infrastructure. Considering that the deployment/operation costs of different infrastructure are highly variable, the capacity-cost tradeoffs of different deployments are examined. The results from the thesis demonstrate the feasibility of deploying non-cellular infrastructure for supporting high-bandwidth vehicular applications. Thirdly, the fundamental impact of traffic signals at road intersection on drive-thru Internet access is particularly studied. The thesis analyzes the time-average throughput capacity of a typical vehicle driving through randomly deployed roadside Wi-Fi networks. Interestingly, we show a significant throughput gain for vehicles stopping at intersections due to red signals. The results provide a quick and efficient way of determining the Wi-Fi deployment scale according to required quality of services. In summary, the analysis developed and the scaling laws derived in the thesis provide should be very useful for understanding the fundamental performance of vehicular networks

Connected Vehicles: Solutions and Challenges

Abstract-Providing various wireless connectivities for vehicles enables the communication between vehicles and their internal and external environments. Such a connected vehicle solution is expected to be the next frontier for automotive revolution and the key to the evolution to next generation intelligent transportation systems (ITSs). Moreover, connected vehicles are also the building blocks of emerging Internet of Vehicles (IoV). Extensive research activities and numerous industrial initiatives have paved the way for the coming era of connected vehicles. In this paper, we focus on wireless technologies and potential challenges to provide vehicle-to-x connectivity. In particular, we discuss the challenges and review the state-of-the-art wireless solutions for vehicle-to-sensor, vehicleto-vehicle, vehicle-to-Internet, and vehicle-to-road infrastructure connectivities. We also identify future research issues for building connected vehicles

Provision Quality-of-Service Controlled Content Distribution in Vehicular Ad Hoc Networks

By equipping vehicles with the on-board wireless facility, the newly emerged vehicular networking targets to provision the broadband serves to vehicles. As such, a variety of novel and exciting applications can be provided to vehicular users to enhance their road safety and travel comfort, and finally raise a complete change to their on-road life. As the content distribution and media/video streaming, such as Youtube, Netflix, nowadays have become the most popular Internet applications, to enable the efficient content distribution and audio/video streaming services is thus of the paramount importance to the success of the vehicular networking. This, however, is fraught with fundamental challenges due to the distinguished natures of vehicular networking. On one hand, the vehicular communication is challenged by the spotty and volatile wireless connections caused by the high mobility of vehicles. This makes the download performance of connections very unstable and dramatically change over time, which directly threats to the on-top media applications. On the other hand, a vehicular network typically involves an extremely large-scale node population (e.g., hundreds or thousandths of vehicles in a region) with intense spatial and temporal variations across the network geometry at different times. This dictates any designs to be scalable and fully distributed which should not only be resilient to the network dynamics, but also provide the guaranteed quality-of-service (QoS) to users. The purpose of this dissertation is to address the challenges of the vehicular networking imposed by its intrinsic dynamic and large-scale natures, and build the efficient, scalable and, more importantly, practical systems to enable the cost-effective and QoS guaranteed content distribution and media streaming services to vehicular users. Note that to effective- ly deliver the content from the remote Internet to in-motion vehicles, it typically involves three parts as: 1.) an infrastructure grid of gateways which behave as the data depots or injection points of Internet contents and services to vehicles, 2.) protocol at gateways which schedules the bandwidth resource at gateways and coordinates the parallel transmissions to different vehicles, and 3.) the end-system control mechanism at receivers which adapts the receiver’s content download/playback strategy based on the available network throughput to provide users with the desired service experience. With above three parts in mind, the entire research work in this dissertation casts a systematic view to address each part in one topic with: 1.) design of large-scale cost-effective content distribution infrastructure, 2.) MAC (media access control) performance evaluation and channel time scheduling, and 3.) receiver adaptation and adaptive playout in dynamic download environment. In specific, in the first topic, we propose a practical solution to form a large-scale and cost-effective content distribution infrastructure in the city. We argue that a large-scale infrastructure with the dedicated resources, including storage, computing and communication capacity, is necessary for the vehicular network to become an alternative of 3G/4G cellular network as the dominating approach of ubiquitous content distribution and data services to vehicles. On addressing this issue, we propose a fully distributed scheme to form a large-scale infrastructure by the contributions of individual entities in the city, such as grocery stores, movie theaters, etc. That is to say, the installation and maintenance costs are shared by many individuals. In this topic, we explain the design rationale on how to motivate individuals to contribute, and specify the detailed design of the system, which is embodied with distributed protocols and performance evaluation. The second topic investigates on the MAC throughput performance of the vehicle-to- infrastructure (V2I) communications when vehicles drive through RSUs, namely drive-thru Internet. Note that with a large-scale population of fast-motion nodes contending the chan- nel for transmissions, the MAC performance determines the achievable nodal throughput and is crucial to the on-top applications. In this topic, using a simple yet accurate Marko- vian model, we first show the impacts of mobility (characterized by node velocity and moving directions) on the nodal and system throughput performance, respectively. Based on this analysis, we then propose three enhancement schemes to timely adjust the MAC parameters in tune with the vehicle mobility to achieve the maximal the system throughput. The last topic investigates on the end-system design to deliver the user desired media streaming services in the vehicular environment. In specific, the vehicular communications are notoriously known for the intermittent connectivity and dramatically varying throughput. Video streaming on top of vehicular networks therefore inevitably suffers from the severe network dynamics, resulting in the frequent jerkiness or even freezing video playback. To address this issue, an analytical model is first developed to unveil the impacts of network dynamics on the resultant video performance to users in terms of video start-up delay and smoothness of playback. Based on the analysis, the adaptive playout buffer mechanism is developed to adapt the video playback strategy at receivers towards the user-defined video quality. The proposals developed in the three topics are validated with the extensive and high fidelity simulations. We believe that our analysis developed in the dissertation can provide insightful lights on understanding the fundamental performance of the vehicular content distribution networks from the aspects of session-level download performance in urban vehicular networks (topic 1), MAC throughput performance (topic 2), and user perceived media quality (topic 3). The protocols developed in the three topics, respectively, offer practical and efficient solutions to build and optimize the vehicular content distribution networks

Performance Analysis of Drive-thru Internet Access

Drive-thru Internet is considered to be an important solution to provide Internet access for vehicles. By deploying cost-effective and high bandwidth roadside WiFi networks, a vehicle can upload/download considerable data when drive through the coverage area, whereby a myriad of automotive applications can be employed, such as intelligent transportation system, infotainment applications like video/audio streaming, webpage browsing, etc. However, the high mobility of vehicles leads to the intermittent connection between a vehicle and roadside Access Points (APs), which would cause the Internet access delay and throughput degradation. In this thesis, we propose comprehensive modeling and analysis for the drive-thru Internet access performance considering the overhead of the access procedure, which includes the steps of network detection, user authentication and network parameters assignment. We also consider the situation that a vehicle drives through multiple roadside APs' coverage areas and evaluate the performance of traffic offloading from cellular networks to roadside WiFi networks. In specific, firstly, we develop an analytical model to study the dependency of the drive-thru Internet access delay with different factors, i.e., the wireless channel conditions, the number of co-associated WiFi clients, and the employed authentication mechanism, such as the WiFi Protected Access II (WPA2)-Pre-Shared Key (PSK) and the WPA2-802.1X modes. The access procedure is modeled as a discrete Markov chain to calculate the time to exchange all management frames and to evaluate the Internet access delay. The accuracy of the analytical model is studied via computer simulations, as well as experimental testing using Commercial Off-The-Shelf (COTS) WiFi products, together with a channel emulator that emulates the wireless channel conditions in a vehicular environment. Simulation and experiment results validate the accuracy of the proposed analytical model which provides useful guidelines for future selection/development of suitable WiFi network access schemes in a vehicular environment. Secondly, we take a further step to analyze the throughput performance of the drive-thru Internet access. The mobility of the vehicle is modeled as the transition of a series of zones in the coverage area, which is defined based on the relationship between the WiFi link rate and the distance of the AP and the vehicle. A three dimensional (3D) Markov model is proposed to combine the zone transition process and the transmission of the management frames and calculate the average throughput under conditions of different numbers of co-associated WiFi clients, channel qualities and different access protocols. Thirdly, we consider that when the vehicle drives through multiple roadside WiFi networks, and employ the Vehicle-to-Vehicle (V2V) assisted WiFi offloading mechanism, where nearby vehicles that associated to different APs can use their idle WiFi resource to offload part of peer's data traffic. The offloading performance is calculated by modeling the intermittent WiFi transmission as an M/G/1/K queueing process, and the performance gain of the V2V assistance is also analyzed. In summary, the research works in this thesis should provide guidelines for future research and development of drive-thru Internet

Performance Evaluation of Vehicular Ad Hoc Networks using simulation tools

Recent studies demonstrate that the routing protocol performances in vehicular networks can improve using dynamic information on the traffic conditions. WSNs (Wireless Sensor Networks) and VANETs (Vehicular Ad Hoc Networks) are exactly related with this statement and represent the trend of wireless networks research program in the last years. In this context, a new type of network has been developed: in fact, HSVN (Hybrid Sensor and Vehicular Network) let WSNs and VANETs cooperate through dynamic information data exchanges with the aim to improve road safety, and especially to warn the driver and the co-pilot of any event occurred in the road ahead, such as traffic jam, accidents or bad weather. The results will be immediate: less accidents means more saved lives, less traffic means a pollution decrease, and from the technological point of view, this communication protocol will open the door to attractive services, such as downloading of multimedia services or internet browsing, that means easier, safer and more comfortable trips. It is out of doubt that speaking about cars and road technology developments, the market and the interests about this field increase exponentially. Recent projects such as CVIS [1] and COMeSafety [2], focused on improving the road driving, and are the concrete demonstration that this entire context can get soon very close to reality. Owing to their peculiar characteristics, VANETs require the definition of specific networking techniques, whose feasibility and performance are usually tested by means of simulation. Starting from this point, this project will present a HSVN platform, and will also introduce and evaluate a communication protocol between VANETs and WSNs using the NCTUns 6.0 [3] simulator. We will particularly analyze the performances of 2 types of Scenarios developed during our project. Both of them are in an urban context, but we will extract different useful results analyzing the packet losses, the throughput and the end-to-end packet delay

AN EFFICIENT ENVIRONMENTAL CHANNEL MODELLING IN 802.11P MAC PROTOCOL FOR V2I

Recent development in communication of wireless communication for automobile industry have aided the growth of SITS (Smart Intelligent Transport System) which solves numerous vehicular based communication service concerns like traffic congestion, accidental mishap etc. VANET (Vehicular Ad-hoc Network) a characteristic class of MANET (Mobile ad-hoc Network) which is a fundamental element of SITS in which the moving vehicles inter connected and communicates with each other remotely. Wireless technologies play an important part in assisting both Vehicle to Infrastructure (V2I) and Vehicle to Vehicle (V2V) correspondence in VANET. The existing scheduling technique does not consider the environmental factor which affects the throughput performance and increases packet drop rate which result in degradation of service quality. Here in this work the author propose a RHU (Rural, Highway and Urban) environment model considering the environmental factor. The efficient environmental model algorithm is incorporated into slotted aloha in IEEE 802.11p MAC protocols which aided as a spine for assisting both safety application and non-Safety applications. Experiments are conducted for collision and throughput efficiency for varied traffic load and speed of vehicle. The experimental result shows the proposed environmental model impact on collision and throughput efficiency for varied environment and thus helps improving QoS for VANET application