在車間網路裡以分散式方法估算即時車輛密度協定

Abstract

近年來，由於科技的進步加上人們的需求，智慧型傳輸系統(Intelligent Transport Systems，ITS)逐漸成為各國交通建設發展的重點之一，車用隨意網路（Vehicular Ad Hoc Networks，VANET）也開始被大家所重視。一般來說，VANET以行車安全性和舒適度為主要的應用範疇，而裝備在車輛上的車上機以車輛對車輛(Vehicle-to-Vehicle；V2V)通訊為基本的溝通方式。VANET的實用性需依賴高可靠的繞徑協定，而好的繞徑協定跟當下車輛密度又是息息相關的。在本篇論文裡，我們提出了一個精準的即時測量車輛密度的協定，名為Real-time Traffic Estimation Protocol (RTEP)。RTEP以位置導向傳遞(position-based forwarding)為基礎，並利用週期廣播訊息與偵測的訊息來估算出路段上的車輛數。在基本的位置導向傳遞裡，我們使用行車最大速度進行預測，並加入安全傳輸距離的觀念，使跳躍轉傳點之間達到穩定的無線鏈結，可大幅增加傳輸的成功率。用此方法，周期發送的訊息可將自己的位置告知鄰近點，每輛車即可獲得附近的車輛數；而偵測訊息則負責加總路段上的車輛總數，最後再以此訊息將此車輛估算值(traffic value)散播在此路段上。最後，我們用NS2網路模擬器來評估RTEP的效能，實驗結果顯示在不同的平均車速、車輛密度跟資料流下，均能有良好的準確率。

Over the last few years, owing to the technical progress and people's demand, the Intelligent Transport Systems (ITS) have been received particular attention both in industrial and academic levels. As a result, there has been a dramatic increase in the number of developments in Vehicular Ad Hoc Networks (VANETs). In order to achieve both road safty and better driving experience, the deployment of such a network equipes each vehicle with an On-Board Unit (OBU), which allows different vehicles to communicate with each other, namely vehicle-to-vehicle communications (V2V). The practicability of VANETs must rely on a routing protocol with high delivery ratio, and the design of such a protocol has close relevance with the real-time trafiic density on the road. In this thesis, we proposed a highly accurate traffic estimating protocol, named Real-time Traffic Estimation Protocol (RTEP). The RTEP is based position-based forwarding, and it makes use of periodic hello and detect messages to estimate the number of vehicles on the road. This protocol also uses the maximum speed of vehicles to predict the safe transmission range. Finally, we use the NS2 network simulator to simulate the RTEP with different average speeds of vehicles, traffic flows and data flows. Simulated results show that the RTEP indeed achieves a high accuracy.