臺灣博碩士論文加值系統

智慧型運輸系統 (ITS) 將會發展成為下一代的運輸系統，它可以幫助我們增加交通的便利行車的效率以及提供更安全的駕駛環境，而特定短距通訊網路 (DSRC) 是智慧型運輸系統下的一種接取網路，它可以提供車子和路旁單元之間高速且可靠的無線通訊鏈路，在特定短距通訊網路中車子通過一個路旁單元涵蓋範圍的時間是很短的，而且當車子從一個路旁單元移動到另外一個路旁單元時所需要執行換手程序的時間相對來說是很長的，因此移動性的問題在特定短距通訊網路是很重要的，如果我們可以適當的考慮車載單元的各種特性去安排服務的順序，我們就可以有效的去減少換手的機率。
除此之外在智慧型運輸系統中所傳送的資訊資料是有有效範圍的，根據資訊的功用和目的所對應的資料有效範圍也都不一樣，再加上每台車子的車速也都不同，所以每個使用者所要求的資訊服務都會有不同的最大可容許延遲時間，一項資訊服務所需的資料必須在這個最大可容許延遲時間內成功的被接收，否則就會變成失敗的服務即使成功的接收到了資料也是沒有意義的。
在本篇論文中我們提出了一個下鏈路的排程演算法叫做最大自由度最後 (MFL) 的排程演算法，此演算法可以在一個最大可容許時間延遲的需求下去達到最小的系統換手率，此演算法根據剩餘每個使用者的服務通道 (SCH) 存在時間，剩餘的資料傳送時間，佇列延遲時間和最大可容許時間延遲去安排使用者的服務順序。模擬結果顯示我們所提出來的演算法和傳統的先到先服務 (FCFS) 還有最早到達截止期限優先 (EDF) 的方法相比在服務失敗率和系統換手率方面擁有較好的效能，並且盡量完全的去使用服務通道達到完全的使用率，因此我們提出的排程演算法可以適用於在智慧型運輸系統下特定短距通訊網路中提供各種資訊的服務。

The intelligent transportation system (ITS) is a next generation transportation system, which aims to increase efficiency, convenience and traffic safety. Dedicated short-range communication (DSRC) is an access network for the ITS to provide a high-speed and reliable radio link between vehicle and roadside unit. In DSRC networks, the dwell time of a vehicle in a cell is short and the handoff latency is long. Therefore, the mobility issue is important in DSRC networks. If we consider lots of characteristics for each OBU to schedule the OBUs service order, the system handoff rate can be reduced effectively.
Besides, the information data in ITS has the effective range according to its purpose and function. Furthermore, each OBU has different velocity. Therefore the service data requested by OBUs should have a maximum tolerable delay. The request data need to be received by OBUs from the RSU successfully before the maximum tolerable delay or the service will become failure.
In this thesis, we propose a downlink scheduling algorithm, called the max freedom last (MFL) scheduling algorithm, to minimize the system handoff rate under the maximum tolerable delay requirement. The algorithm schedules the OBUs service order according to the remaining SCH dwell time, remaining transmission time, queueing delay, and the maximum tolerable delay for each OBU.
The simulation results show that the MFL scheduling algorithm has good performance in the service failure rate and the system handoff rate compared to traditional FCFS and EDF methods and also can achieve the full utilization for the SCH. Therefore, the MFL scheduling algorithm can be applied to the DSRC networks with different kinds of services in ITS.

中文摘要 i
Abstract ii
Acknowledgement iii
Contents iv
List of Figures v
List of Tables vi
Chapter 1 Introduction 1
Chapter 2 Max Freedom Last Downlink Scheduling Algorithm 7
2.1. Introduction 7
2.2. System Model 13
2.2.1. System Operation 13
2.2.2. Traffic Model 21
2.3. MFL Downlink Scheduling Algorithm 23
2.4. Simulation Result 31
2.4.1. Simulation Environment 31
2.4.2. Simulation Result and Conclusion 33
2.5. Concluding Remarks 42
Chapter 3 Max Freedom Last Downlink Scheduling Algorithm with Different Maximum Tolerable Delay 44
3.1. Introduction 44
3.2. System Model 45
3.3. Simulation Result 46
3.3.1. Simulation Environment 46
3.3.2. Simulation Result and Conclusion 47
3.4. Concluding Remark 49
Chapter 4 Conclusion 51
Bibliography 52
Vita 54

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