| Summary: | 由於VANET上的行動節點移動速度快，加上受到道路及交通號制的限制，導致網路拓樸快速改變，容易造成網路斷訊，影響資料封包在網路上的傳送效能。在傳統的MANET上有許多用來傳送資料封包的路由機制，並不直接適用在VANET上。隨著Global Position System (GPS)的普及，越來越多的車輛都具備GPS，用以輔助行車定位之用。在本研究中我們將透過GPS取得車輛的地理資訊，提出一個適用於VANET中以車行方向為基礎的貪婪路由演算法(MDBG)。
本論文目的在強化VANET網路上資料封包的路由選擇策略。所提出的路由機制將會透過hello message來取得相鄰車輛的位置和車行方向，並利用目標要求(DREQ)、目標回應(DREP)來獲得目標車輛的資訊。進而運用車輛的車行方向，選擇適當的相鄰車輛找出一條穩定的路由路徑。當來源車輛和目標車輛的車行方向相同時，AODV能有不錯的效能表現。而我們的路由演算法(MDBG)將強化當來源車輛和目標車輛的車行方向相反，並且逐漸遠離時的效能表現。實驗模擬的結果顯示MDBG在封包到達率、吞吐量和平均端對端延遲上較之於AODV及DSR演算法有更優異的表現。
=== Packets transmission over VANET is intermittent due to rapid change of network topology. This comes from both high mobility of mobile nodes and road limitation. Intermittent transmission causes inefficient packet delivery. Those routing protocols applicable to MANET might not be suitable for VANET. On the other hand, Global Position System (GPS) is becoming prevalent in assisting positioning for vehicles. In this research, we develop a Moving Direction Based Greedy (MDBG) routing algorithm for VANET. MDBG algorithm is based on the geographical information collected by GPS.
The objective of the thesis is to enhance routing decision in packet delivery. The "hello message" is used to retrieve the locations and moving directions of neighboring vehicles. Destination REQuest (DREQ) and Destination REPly (DREP) messages are used to retrieve target vehicle information. The source vehicle will thus use these information together with its own moving direction information to establish a stable routing path by selecting appropriate neighboring vehicles. AODV algorithm is proved to have good performance as both the source vehicle and target vehicle have the same moving direction. MDBG algorithm is proposed to leverage the problem as source vehicle and target vehicle move far apart in opposite directions. Simulation results show that MDBG outperforms both AODV and DSR in packet arrival rate, throughput and average end-to-end delay.
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