| Summary: | 博士 === 國立臺灣大學 === 土木工程學研究所 === 95 === Traffic information system based on mobile phone location technology relies on cellular network data reported by mobile phones to determine accurate location and generate traffic information. However, inaccurate location and insufficient cellular network data become the two major barriers for implementation.
For the first issue, in traditional traffic information estimation method, the difference in positions is used to estimate traffic information. However, variation or flutter of positioning caused by imprecise mobile phone location accuracy may lead to the unstable measurement. Take the latest mobile phone location positioning technology into consideration, this dissertation introduces a new segment-based traffic information estimation method. It is proved by simulation approach in this research that segment-based method performs better than traditional distance-based method when location error ranges within the length of a segment. Simulation results also demonstrate that segment-based method is better than traditional one under all kinds of traffic condition except for the conditions of high location error and over saturation. Through simulation analysis, we conclude that enough sample size, i.e. larger vehicle generation rate, longer data collection interval, shorter location update interval, and larger mobile penetration rate are crucial factors to generate accurate traffic information.
For the second issue, mobile phone reports cellular network data to the mobile switching center when it is necessary to update the location when mobile phone is switched on, active or update-timer expired during idle. The purpose of Location Update is to ensure each call can be delivered to an exact destination on time and efficiently. The higher the update frequency is, the faster each call can be connected and therefore, more traffic data can be obtained to generate reliable traffic information. However, frequent updates increase network load and decrease service level. Therefore, there is a trade-off between operation cost and traffic information quality for the purpose of generating the best update strategy. This research develops analytical models to analyze the optimal Location Update strategy with the objective of minimum total cost. The optimal analytical results and numerical analysis results show that the optimal timer (t) is inversely proportional to cube root of square speed (S); moreover, the optimal distance (m) is proportional to cube root of travel speed (S). When traffic condition becomes worse, it’s suggested to increase the update timer. Finally, a maneuverable model and rule of optimality developed by this study can be used as a price evaluation tool for both telecom operators and traffic information providers.
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