Streetcast-車用網路街道廣播協定

Abstract

交通工具以及大眾運輸系統已經變成人們日常生活中不可或缺的一部分。現在市面上已經有許多輔助行車的工具或是行車間娛樂的產品，如：全球定位系統(GPS) 、無線數位電視…等。然而人們也希望能夠於行車時，藉由網路資源獲取更多的行車資訊甚至娛樂；加上無線網路設備的進步，無線設備變的功能強大又便宜，因此，車間網路變成一個熱門的研究題目。智慧型運輸系統(Intelligent Transportation System, ITS)就是利用車間網路所建立的一個行車輔助系統來提供即時、廣泛以及無接縫的交通資訊，並且給駕駛一個方便以及安全的駕駛環境。智慧型運輸系統有許多的應用，如：緊急或危險訊息的傳播、即時道路資訊、地域性服務或廣告…等。其中，以輔助行車安全的緊急或危險訊息的傳播是最為重要的，而這類型的訊息傳播通常是藉由廣播來達成。因此，設計一個有效率的多跳廣播機制在車間網路上，是一個重要的課題；特別是在都市區域的廣播，由於車輛的擁擠，更是面臨許多問題。在本研究中，我們利用多重播送的機制來以及利用全球定位系統以及電子地圖來輔助廣播，名為街道廣播。藉由多重播送的機制，我們可以保護無線網路頻道以及達到一定的可靠度；藉由全球定位系統以及電子地圖，我們可以挑有效率的節點來轉播，以及限制訊息的廣播範圍。同時，我們也設計了動態調整控制封包的傳送機制，能夠有效的減少多餘的控制封包。最後我們模擬街道廣播以及利用真實的都市道路以及車流量來評估我們的廣播機制，而模擬的結果顯示出我們所提出的播送協定在不同的網路流量中，也能在封包傳送率、端點延遲以及碰撞數方面皆擁有良好的效能。

Transportation System has become indispensable in our daily life. There are many commodities for driving assistance and entertainment, for example, Globe Position System (GPS), wireless digital TV, etc. Therefore, people expect to get more information or entertainment services from internet while driving. As the wireless devices become dainty and cheap, vehicular ad-hoc networks (VANETs) become a popular research topic. Intelligent Transportation System (ITS) is established to provide real-time, comprehensive and seamless traffic information, and to give a convenient, safe, and efficient driving experience. There are many applications for ITS, for example, emergency message, real-time traffic information and location based services or advertisements, etc. The dissemination of emergency message is one of the most important applications of them, and they are usually disseminated by broadcast. Therefore, it is an important topic to design an efficient multi-hop broadcast mechanism for vehicular ad-hoc networks, especially in urban areas. Broadcast in the urban area meets more problems than in the rural area because of the high density and high mobility of vehicles. In this work, we use multicast RTS to protect wireless channel and provide reliability. Moreover, we use the Global Position System (GPS) combined with the digital road map information to assist relay node selection. Meanwhile an adaptive beacon control is proposed to reduce control redundancy. At last, we evaluate our broadcast protocol in the real road map and real traffic flow. The simulation results show that the proposed broadcast protocol has superior performance in terms of packet delivery ratio, end-to-end delay and the number of collisions under different traffic load.