在無線車用網路(VANETs)中，車輛與車輛之間的資訊交流是非常重要的，但是要得到目的車輛的位置並不容易。由於車用網路中，節點移動速度較快，導致節點間的拓樸連結容易隨著時間產生高度的變動。因此要找到某一特定的節點較以往的隨意行動網路(MANETs)要來的困難。本論文提出了一個階層式的位置服務系統，能夠快速且低成本的提供服務。首先我們利用主要幹道車輛較多的特性，設計一個新穎的網路切割法與一個發送更新位置封包的機制。此機制可以在降低車輛產生大量更新封包的同時，依然能夠掌握車輛的正確位置。我們將切割後的細小網格設計為範圍漸增的三種層級，分別儲存其管理範圍內的車輛更新位置封包。使用此服務系統的車輛可以藉由分散式在小範圍內找到其目的車輛；若目的車輛距離較遠，才須詢問較大的範圍。另外，我們提出一個非齊頭式的封包收集法來收集不同範圍內的更新封包，降低硬體建置的成本，提高在大範圍接收與儲存封包的穩定度。實驗的結果顯示，我們的方法能夠降低車輛更新位置所傳送的封包，並且保持高度的服務成功率。 In VANETs, it is very important to communicate between two vehicles, but how to get the correct position of a vehicle is not easy. Due to vehicles are moving fast, topology in VANETs changes rapidly. As a result, location services processed in VANETs are more difficult than in MANETs. In our thesis, we propose a hierarchical location service system, it provides a low cost and rapid service. First, we select the main arteries to divide network into grids because of there are more vehicles than in normal roads, and then design a mechanism that when vehicles need to send update packets. This mechanism can decrease the number of update packets and still gain correct vehicles’ location. Second, we design grids with three levels, the higher the level, the larger the area. Each level stores update packets sent within its area. Vehicles using our system can find the destination vehicle distributedly within a small area; if the target is not within this area, then find within a larger area. Besides, we propose a packets collection method, it can be adjusted with different size of collection area. The simulation results show that our scheme could decrease the number of location update packets effectively, and keep high success rate of location service.
