一個在VANETs中取得即時交通資訊的傳輸架構

Abstract

近年來智慧型運輸系統(Intelligent Transportation System, ITS)的發展已越來越普遍。車載隨意網路(Vehicular Ad-hoc Networks, VANETs)逐漸成為ITS應用的優選。VANETs的通訊模式可分為:車輛與車輛間通訊(Vehicle-to-Vehicle,V2V) 和車輛與路邊裝置間通訊 (Vehicle-to-Infrastructure, V2I)。V2V網路具有車輛移動迅速，網路拓樸快速改變，車間通訊範圍限制之特性，使得在動態的VANET環境下要能相互傳送即時的交通資訊將倚賴車輛間彼此的通訊連線。本研究提出一個在VANETs中能充分有效地傳送即時交通資訊的傳輸架構，此傳輸架構由三種模式構成。第一個模式操作在V2V通訊環境下，車間的通訊距離在傳輸範圍內時，將叢集為一群具共識的群集以利緊急事故訊息能快速有效地散播，改善廣播風暴問題;第二個模式則使用V2I通訊的路邊裝置(Roadside Units, RSUs)，蒐集行動網路手機通訊中的訊號強度進行即時交通車速之估計，並置於雲端供用路人查詢; 第三個模式是一個混合模式，V2V+V2I，它解決V2V車輛間資料傳送的範圍限制，協同V2I模式建構傳輸即時交通資訊的連線。透過模擬與現有的廣播方法比較，實驗結果顯示本研究提出的V2V模式和混合模式將可降低訊息傳送數量與延遲時間，從而提升即時交通資訊的傳送效率和可靠度。此即時交通資訊的傳輸架構將有助於ITS在車載通訊上取得與傳送即時交通資訊之運用。

In recent years, the development of intelligent transportation system (ITS) has become more and more popular. The vehicular ad-hoc networks (VANETs) are emerging as the preferred network design for ITS. The VANETs are based on short-range wireless communication between vehicles, which can be classified into two communication modes, vehicle-to-vehicle (V2V) and vehicle-to-infrastructure (V2I). V2V refers to the direct or multi-hop communications among vehicles. V2I refers to the communication with the infrastructure of roadside units (RSUs). V2V embrace high mobility of vehicles, rapid changing topology due to uneven distribution of vehicles and inter-vehicle transmission range. Therefore, in a dynamic VANET environment, the vehicle transmission’s reliability will affect the real-time traffic information dissemination in a consensual and effective way. In this thesis, we propose a transmission architecture in which real-time traffic information can be disseminated both adequately and effectively. There are three modes of operation in the proposed architecture. The first mode is operated under V2V where the vehicles are within the transmission range and proposed a consensus-based cluster protocol to disseminate real-time safety alert message to cluster members. The second mode is operated under V2I; the design of RSUs is responsible for obtaining cellular-network-based data to estimate speed information on cloud. The third mode, which is a hybrid approach, V2V+V2I, is operated via the coordination between V2I and V2V in disconnected condition, particularly. In accordance with the simulation results, we notice that, the performances of the proposed V2V mode and hybrid mode can downgrade the number of message dissemination and improve the broadcast storm problem. Therefore, the novel transmission architecture would be useful for acquiring and transmitting real-time traffic information between vehicular communications for ITS.