近年來，車載隨意網路(Vehicular Ad hoc Network, VANET)的通訊技術已被廣為討論，其相關研究更是眾多的學者關切且研究的熱門議題。其主要之應用範疇，包括提供行車安全的服務以及便利生活的訊息，讓所有的用路人可以即時取得與傳遞與交通相關的資訊，以便提高行車效率，增進用路安全與舒適性。
  過去研究中，如何在車輛間有效率的傳輸緊急事件訊息 (如撞車、濕滑、坑洞、讓道給救護車及警車等訊息)，是一個急待解決的議題。若採用IEEE 802.11傳輸協定，來進行緊急事件封包發送，將使車輛隨機發出封包，除了容易發生封包Collision現象，並且multi-hop的傳送也會因此造成無窮盡的封包延遲現象，為了確保緊急事件封包能在短時間內有效率的通知鄰近車輛，採用預先規劃車輛傳輸機制，將可以有效控制封包延遲現象。
  本論文主要針對車間緊急事件的傳遞，提出一個利用TDMA-based MAC Protocols 。其利用道路節區的預先規劃，使用叢集(Cluster)之概念，以Cluster Header統一傳送訊息來取代各車自行轉送訊息，透過訊息之監控、重送機制、多頻道傳輸等特殊設計，來解決封包衝撞與延遲等問題，以減少不必要的傳輸成本與頻寬浪費，提高訊息傳送的效率與可靠性。實驗模擬顯示，本論文所提之方法，在某些條件下，確實能有效提供車輛間更快速且更可靠的資料傳送。

In recent years, the connective technology of Vehicular Ad hoc Network has been widely discussed. In the primary applications of VANET can be categorized by two classes: driving safety and convenient living. All of people have capability to acquire and transmit real-time traffic information which can definitely raise driving efficiency and vehicle comfort. How to efficiently transmit between vehicles the emergent messages such as accident, wet-street, pit, emergency service and police petrol is an urgent issue. In case the protocol IEEE 802.11 is adopted, the packet in transmission can easily cause not only collisions but also long-term delay. Due to the assuredness of emergent packet in shot time communication, the prior scheduling vehicle transmission function can efficiently control the packet lag. This research primarily focuses on emergent transmission between vehicles. The TDMA-based MAC Protocols will be utilized in this research. The pre-scheduling in segmentation of street would be adopted by the cluster prospective. The Cluster Header is able to substitute the individual signal which is transmitted by each vehicle. By applying the proposed message surveillance, re-transmission and multi-channel access mechanisms, the conflictive packet and signal delay problems could be solved to reduce consumption in cost and bandwidth and improve the network throughput and reliability. In the experimental simulation, in some hypothesis, the functions we presented indeed facilitate the message transmission between vehicles can be prompt and reliable.

一、VANET簡介	1
  1.1、簡介	1
  1.2、發展背景	2
  1.3、網路架構	3
  1.4、研究議題	5
二、相關研究	7
三、網路環境與問題探討	12
  3.1、網路環境與假設	12
  3.2、問題探討	13
四、緊急廣播之MAC通訊協定	15
  4.1、基本構想	16
  4.2、道路節區(SEGMENT)與TDMA的規劃與運用	18
  4.3、CLUSTER HEADER 的選擇	22
  4.4、資料之重送機制	29
    4.4.1、 MAC Layaer Packet Header 新增欄位	29
    4.4.2、資料傳送之監控與重送	30
  4.5、多頻道之運用	31
    4.5.1、透過時槽分配機制增進傳送效能與速度	31
    4.5.2、週期中節區可傳送次數與多頻道的關係	33
    4.5.3、多頻道對於頻道衝突或干擾的運用	34
  4.6、運作流程與演算法	35
五、模擬實驗	41
六、結論	45
參考文獻	47
附錄-英文論文	49

圖目錄
圖 1.1  ROADSIDE-TO-VEHICLE COMMUNICATIONS (RVC)	4
圖 1.2  INTER-VEHICLE COMMUNICATIONS (IVC)	4
圖 2.1  CVIA時槽分配示意圖	8
圖 2.2  CVIA機制中封包轉傳過程	9
圖 2.3  節區距IGW位置與封包傳遞量示意圖	10
圖 2.4  頻寬利用率損耗示意圖	10
圖 4.1  節區 與 FRAME 對應圖	16
圖 4.2  車輛通信距離與節區長度之關係	18
圖 4.3  FRAME, TIME SLOT, WORKING PHASE 關係圖	22
圖 4.4  兩點間距離關係範例	23
圖 4.5  兩點間方位角關係範例	24
圖 4.6  節區中之群組劃分	25
圖 4.7  群組定義之範例圖	26
圖 4.8  以行進方向來定義群組之示意圖	27
圖 4.9  為選舉階段各群組發送選舉訊息的時間圖	28
圖 4.10 週期內節區分配單一時槽與等待時間關係	32
圖 4.11 週期內時槽數量與可傳送次數關係	32
圖 4.12 節區可傳送次數與可使用頻道之關係	33
圖 4.13 彎道附近節區通信範圍重疊示意圖	34
圖 4.14 節區於彎道區域頻道規劃範例	35
圖 4.15 機制運作流程	36
圖 5.1  THROUGHPUT – 無重送機制	43
圖 5.2  THROUGHPUT – 有重送機制	43
圖 5.3  THROUGHPUT–有重送機制，加入一般TDMA的PROTOCOL	44
圖 5.4  封包遺失數量的統計(使用重送機制)	44

表目錄
表格 4.1 SEGMENT TABLE內容範例	20
表格 4.2 各階段主要工作項目	         36
表格 5.1 SIMULATION PARAMETERS	42

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