近年來，利用車載隨意行動網路作為車間通訊的方式受到人們的注意。大多數在此類網路上的應用與地理繞徑協定都需知道期待傳輸的車輛位置。過去網路中之車輛可利用位置服務協定來詢問位置。這些位置服務協定因為通訊負擔高且車間通訊路徑容易中斷，並無法實際運用於車載隨意行動網路。因此，本論文提出一個設計於城市環境之分散式車載隨意行動網路位置服務，以此服務滿足詢問位置的需求。我們的位置服務未使用位置伺服器來存放位置資訊。每輛車在路口發送與暫存它們所收集到的位置資訊，亦即留下位置資訊的線索在車輛中。因此，我們可以利用擁有高移動性的車輛，散佈它們所收集到的位置資訊。這種方式減少散佈位置資訊所需要的封包量，車輛可在舊的位置資訊附近找到新的位置資訊。在位置資訊被散佈後，我們的詢問方式即利用這些位置資訊來追蹤並獲得所尋找的車輛位置資訊。本論文分析並模擬我們所提出之位置服務，分析出我們的更新成本、最差詢問成本、網路中擁有被詢問車輛位置資訊的位置，以及追蹤被詢問車輛所可能詢問路徑。模擬結果顯示我們的位置服務能在車載隨意行動網路中有效率的運作，詢問位置成功率和傳送耗費成本優於過去所提出之方法。 In the recent years, vehicular ad hoc networks (VANETs) got attention for inter-vehicle communications. Most applications in the networks and geographic routings need to know that where the locations of desired vehicles for communications are. Each vehicle can use a location-service protocol to query locations in network. Previous location-service protocols can be categorized as flooding-based and quorum-based. They are unrealistic for VANETS because of the communication overheads are high and the communication paths between vehicles are broken easily. Thus, in this thesis, we propose a distributed location service for VANETs in city environments for the requirement of querying locations. Our location-service protocol can be classified into a quorum-based approach but we do not have location servers for saving location information. Each vehicle sends update packets and caches location information which it received in intersections, i.e., each vehicle leaves clue of location information in vehicles. Therefore, we can exploit the vehicles with high mobility in network to disseminate location information of they collected. The update scheme of our location-service protocol reduces the packets for location information dissemination. Vehicles can find newer location information from the proximity of the vehicles have older location information. Thus, after the location information of queried vehicle had been disseminated, our query scheme can exploit the location information in network to track and retrieve current location information of queried vehicle. We analyze and simulate our location-service protocol in this thesis. The analysis shows update cost, worst case query cost, locations of the vehicles which have location information of queried vehicle, and possible query paths for tracking queried vehicle. The simulation results show that our location-service protocol works efficiently for VANETs in city environments. The success rate of querying and the cost in simulation time are better than previous works.
