一個基於車載隨意行動網路之行車導航系統的分析

Abstract

提供駕駛者即時交通資訊各路段旅行時間，並配合導航系統的使用，能有效的節省行車時間及能源消耗。由於具備GPS定位系統及無線資料傳輸的智慧型手機日漸普及，利用行駛車輛上的智慧型手機收集並與其他車輛交換即時交通資訊，再以此資訊週期性的評估出目前的交通狀態，即時的選出最佳旅行路線成為可行的方式。在傳統的分散式系統，每台使用導航系統的車輛使用泛洪法週期性的廣播資料，這將會使網路中充斥許多不必要的交通採集樣本，造成頻寬的浪費。為了增加資訊傳輸效率，許多的方法因此而被提出。其中，流言法在高密度的流量下具有極佳的效能。因此一個使用優先權流言法的導航系統CATE，擁有極佳的資訊傳播效率，並且透過一極為擬真的實驗證明了其效能和高度擴展性，但是這套導航系統仍有其不足之處，未考慮在十字路口所可能產生的延遲，以及可能會產生二度擁塞的問題。我們提出一個方法評估各路段的轉彎延遲來解決十字路口的延遲問題，透過Veins的擬真模擬結果顯示我們的方法可以額外再度減少17%的平均旅行時間，並減少2%因為使用導航系統反而造成旅行時間增長的車輛數。

Providing real-time traffic information, such as the travel time of each road segment, to road users and coupling this information with navigation system can save traveling time and reduce fuel consumption. With the increasing popularity of smartphones that are embedded with GPS receiver and wireless data communication capability, smartphones on journeying vehicles can collect and exchange the real-time traffic information, and then dynamically choose a time-saving route based on the collected traffic condition. In a conventional distributed system, navigation-embedded vehicles use the flooding method propagating the traffic information periodically. However, there may be redundant samples spreading in the network. For the purpose of improving the dissemination efficiency, many methods have been purposed. Gossip-based propagation models have a great efficiency in dense traffic. So the navigation system CATE, using utility-based gossip model to keep the scalability and the efficiency, has been proved to offer scalability in a realistic experiment. However, CATE has some deficiencies that need to be improved; for example, intersection delay is not considered in route planning and secondary congestion problem may occur after re-routing by users using the same navigation system. We purpose a method that provides each road segment’s turning delay to improve the travel time for more road users. Veins has been used to simulate our navigation system. The simulation results indicate our method can save more than 17% average travel time and reduce the percentage of cars that experience longer travel time by 2%.