由於世界各國主要城市之交通狀況持續惡化，在道路容量無法大規模增加的情況之下，結合電腦、電子與通訊科技以有效的提昇運輸系統效能已是世界各國的努力目標，此一發展可統稱為智慧型運輸系統 (Intelligent Transportation Systems, ITS)。其最重要的觀念在於有效的利用尖端通訊科技，改善交通的問題，其中包括減少事故的發生、提升運輸的效率等。
智慧型運輸系統(ITS)於通訊上的應用可分為車輛與基礎設施的整合(Vehicle-Infrastructure Integration, VII)和車間通訊(Inter-Vehicle Communication, IVC)兩個部份。為了專用短距離通訊(Dedicated Short Range Communication, DSRC) ，美國聯邦通訊委員會(Federal Communications Commission, FCC) 在5.9GHz的頻段上提供了75MHz(5.850GHz-5.925GHz)的頻寬給車用通訊系統使用。其中車間通訊(IVC)更是智慧型運輸系統裡重要的一環，負責交通資訊系統的蒐集與傳播的工作。由VII與IVC所組成的網路架構是以Ad-hoc為基礎，為MANET(Mobile Ad-hoc Network)所衍生出來，所以又稱為VANET(Vehicle Ad-hoc Network)。
不同於以往無線網路的研究，VANET必須考量到駕駛者、車速、車流等交通特性在內，所以VANET本身即為變化迅速的網路架構。本研究考量交通狀況所造成的交通擁塞，使VANET之中車流密度高即網路節點密集時，對網路效能所造成之影響，並了解透過調整通訊傳輸距離是否有助於擁塞發生時之網路品質。
本研究透過離線型之整合模擬模式探討車流特性與通訊傳輸之關係。在整合模擬模式中車流模擬是由DynaTWAIWAN負責，其最大的特點為充份考慮國內混合車流、交通控制系統與駕駛人的行為反應；通訊模擬由NS2負責，NS2為open source軟體，與車流模擬軟體結合上具有較高的設定彈性。
本研究透過數值實驗瞭解車流密度以及通訊傳輸距離對網路品質之影響，在以混合車流及獨立路口之交通情境來進行實驗，以觀察不同交通環境下對網路品質之影響。

Intelligent Transportation Systems (ITS) focus on increasing the efficiency of existing surface transportation systems through the use of advanced computers, electronics, and communication technologies. Wireline and wireless communications are deployed in the ITS contexts, and wireless communication has become special and important features of ITS.
With the innovation and advancement of communications, Telematics, the integration of telecommunications and informatics, need to be incorporated into new generation of traffic analysis methods. In this thesis, an integrated simulation framework is proposed to simulate vehicular flows and information flows simultaneously in order to study possible benefits and difficulties of VII and IVC in a realistic environment. The vehicle movement is simulated by DynaTAIWAN, a native simulation-assignment model. The communication simulation is achieved through NS2.
An interactive simulation framework should consider possible interactions between drivers and information received through wireless communication, road side unites and/or other vehicles. The tripmaker route choice behavior is explicitly modeled in DynaTAIWAN, thus drivers choose alternative routes based on their experiences and information. The traffic flow patterns are basic input to Traffic Management Centers (TMC), thus information can be transmitted through wireless communication with DSRC, in terms of vehicle-to-vehicle and vehicle-to-road communication.
Numerical experiments are performed to illustrate impact of traffic density on communication quality. Passenger car only case and mixed traffic flow conditions are examined. DynaTAIWAN allows the identification of the key underlying parameters that influence system performance and the exploration of their effect.

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