近年來網路的發達改變了人類的生活習慣；網路的服務類型豐富多變，也愈來愈貼近人們的生活。隨著網路技術的成熟與普及，網路應用層面也從一般的電子產品發展到車用電子。在這樣的演進之下，開始有一些車載通訊的標準或草案被訂定出來，例如由802.11發展而來的802.11p。
隨著802.11p草案的制定與發布，車載通訊也愈來愈廣為人知。因此車用隨意網路(Vehicular Ad Hoc Network, VANET)已經日益成熟，也有愈來愈多人投入相關研究。車用隨意網路的設備主要可以分為兩大類：一個是事前建置在道路旁的基地台(Road Site Unit, RSU又稱Infrastructure)；另一個是移動的車輛(Vehicle)。而通訊也可以分為兩大類：一類是車輛對車輛的通訊(Vehicle to Vehicle, V2V)，二是車輛對基地台的通訊(Vehicle to Infrastructure, V2I)。
由於建置RSU的成本高，因此在車載網路建置初期以及郊區人口稀疏的地方，為了節省成本，RSU的服務也許無法涵蓋所有路段。也就是說，車載網路中的RSU資源是相對珍貴的。為了更有效地利用RSU資源，我們提出了一個新的方法來提升車輛對基地台通訊的使用效率。
我們使用分散式排序機制(Distributed Sorting Mechanism, DSM)，讓網路中的所有車輛可以個別運算優先順序，經由我們所提出來的機制排序之後，可以讓較具有優勢的車輛能夠優先上傳資料。除了本身具有優勢的車輛可以優先使用V2I通訊資源外，我們另外也考慮到即將脫離服務範圍的車輛；在特定的情況下，我們的機制也具有先到期先服務(Deadline First)的特性。此外，使用分散式機制可以簡化交握（Handoff）過程，進而節省網路負荷，達到充分利用RSU資源的目的。

In recent years, the development of network technologies has greatly changed human being’s living habits, and the abundant network services are also getting more and more close to human lives. With the maturity and popularization of network technologies, the network applications have developed from household electronic products to products for mobile vehicles. In such an evolution, several vehicular network standards and drafts have been released, like 802.11p that is extended from 802.11.
Owing to the establishment and release of the draft of 802.11p, VANET is becoming well-known and more and more people have involved in related researches. Generally, the equipments of VANET can be divided into two categories: Road Site Units (RSU) or Infrastructure, and moving vehicles. The communication of VANET also can be divided into two types: Vehicle to Vehicle (V2V) and Vehicle to Infrastructure (V2I).
Because it is expensive to establish RSU, the number of RSU is usually too few to cover areas like suburbs or areas with sparse population. In other words, the resource of RSU is rather precious in VANET. In order to promote the utility of RSU, we propose a novel mechanism to improve the efficiency of communication between vehicles and RSU (Vehicle to Infrastructure, V2I).
Our proposed mechanism in this paper is called “Distributed Sorting Mechanism (DSM)”. In DSM, every vehicle can individually calculate its own priority of communication and the time to compete and obtain the channel can be reduced. We further consider the vehicles moving away from the coverage of communication and adjust their priorities of communication appropriately. Moreover, DSM owns the characteristic of “Deadline First” in specific situations. Using DSM can not only simplify the handoff procedure and reduce the network overhead, but also achieve the adequate utilization of RSU resource.

目    錄
第一章  緒論	- 1 -
1.1	前言	- 1 -
1.2	動機與目的	- 1 -
1.3	論文章節架構	- 3 -
第二章  VANET相關研究及背景介紹	- 5 -
2.1	VANET的起源—MANET	- 6 -
2.2	VANET VS. MANET	- 9 -
2.3	VANET網路架構	- 13 -
2.3.1	車輛對車輛通訊 (V2V Communications)	- 14 -
2.3.2	車輛對基地台通訊 (V2I Communications)	- 16 -
2.3.3	混合型通訊 (Hybrid of V2V and V2I)	- 17 -
2.4	分散式協調功能 (IEEE 802.11 DCF)	- 19 -
第三章  分散式排序機制	- 21 -
3.1	分散式排序機制概述及實驗場景介紹	- 21 -
3.2	計算WT值三步驟	- 24 -
3.3	Shift機制	- 31 -
3.4	DSM數學模型	- 34 -
3.5	適用於混合型通訊的DSM	- 36 -
3.5.1	混合型通訊之架構及特性	- 36 -
3.5.2	DSM之搜集模式	- 39 -
3.5.3	DSM之先到期先服務模式	- 41 -
第四章  模擬結果與效能分析	- 44 -
4.1	實驗環境介紹	- 44 -
4.1.1	模擬場景與模擬參數	- 44 -
4.1.2	其他網路機制	- 46 -
4.2	模擬結果與分析	- 48 -
4.2.1	DSM參數探討及設定	- 48 -
4.2.2	DSM與其他排序機制比較	- 52 -
4.2.3	使用DSM改善混合型通訊機制	- 56 -
第五章  結論與未來展望	- 60 -
參考文獻	- 62 -

圖目錄
圖2.1 無線網路之INFRASTRUCTURE模式	- 6 -
圖2.2 無線網路之AD HOC模式	- 7 -
圖2.3 DSRC頻寬分配圖[1]	- 13 -
圖2.4 車輛對車輛通訊(V2V)	- 15 -
圖2.5 車輛對基地台通訊(V2I)	- 17 -
圖2.6 混合型通訊(V2V AND V2I)	- 18 -
圖2.7 IEEE 802.11 DCF之媒體存取競爭	- 19 -
圖3.1 RSU服務品質	- 22 -
圖3.2 加入DSM過後的競爭方式	- 23 -
圖3.3 計算WT值三步驟	- 25 -
圖3.4 服務品質與Tτ關係圖	- 26 -
圖3.5 計算WT值第一步：以地理位置區分優先順序	- 27 -
圖3.6 計算WT值第二步：以相對速度區分優先順序	- 29 -
圖3.7 計算WT值第三步：以資料量大小區分優先順序	- 30 -
圖3.8 以三步驟計算後的WT值	- 30 -
圖3.9 基本的Shift機制	- 32 -
圖3.10 不同等級的Shift機制	- 33 -
圖3.11 混合型通訊架構	- 37 -
圖3.12 適用於混合型通訊之DSM	- 39 -
圖4.1 CVIA概述	- 47 -
圖4.2 N值與效能關係圖	- 49 -
圖4.3 工作模式切換臨界值與效能關係圖	- 51 -
圖4.4 服務完成率與車輛密度關係圖	- 53 -
圖4.5 資料新鮮度與車輛密度關係圖	- 55 -
圖4.6 平均吞吐量與車輛密度關係圖	- 57 -
圖4.7 封包重傳率與車輛密度關係圖	- 59 -

 
表目錄
表2.1 MANET與VANET特性比較表	- 10 -
表3.1 車速與速度等級對應表	- 28 -
表4.1 模擬參數表	- 45 -

[1]	D. Jiang, and L. Delgrossi, “IEEE 802.11p Towards an International Standard for Wireless Access in Vehicular Environments” Vehicular Technology Conference, 2008. VTC Spring 2008. IEEE 11–14 May 2008, pp. 2036–2040.
[2]	G. Korkmaz, E. Ekici, and F. Ozguner, “A cross-layer multihop data delivery protocol with fairness guarantees for vehicular networks,” IEEE Transactions on Vehicular Technology (IEEE TVT), Vol. 55, No. 3, pp. 865-875, May 2006.
[3]	J. Zhao, Y. Zhang, and G. Cao, “Improving Drive-Thru Access to Roadside Infrastructure by Lightweight Relay” 2007 Mobile Networking for Vehicular Environments 11-11 May 2007, pp. 144–149.
[4]	J. Chennikara-Varghese, W. Chen, T. Hikita, R. Onishi, “Local Peer Groups and Vehicle-to-Infrastructure Communications” Globecom Workshops, 2007 IEEE 26–30 Nov. 2007, pp. 1–6.
[5]	T. Taleb, E. Sakhaee, A. Jamalipour, K. Hashimoto, N. Kato,Y. Nemoto, “A Stable Routing Protocol to Support ITS Services in VANET Networks” IEEE Trans. on Vehicular Technology, Volume 56, Issue 6, Part 1, Nov. 2007, pp. 3337–3347.
[6]	T.J. Kwon, W. Chen, R. Onishi, T. Hikita, “Unicast Routing among Local Peer Group (LPG)-Based VANETs” GLOBECOM Workshops, 2008 IEEE Nov. 30 2008-Dec. 4 2008, pp. 1–5.
[7]	L. Bononi, M. Di Felice, ”A Cross Layered MAC and Clustering Scheme for Efficient Broadcast in VANETs” Mobile Adhoc and Sensor Systems (MASS) 2007, 8-11 Oct. 2007, pp. 1–8.
[8]	Wisitpongphan, N., Tonguz, O.K., Parikh, J.S., Mudalige, P., Bai, F., Sadekar, V. “Broadcast storm mitigation techniques in vehicular ad hoc networks,” IEEE Wireless Communications, Vol. 14, pp.84-94. (2007) 
[9]	O. Tonguz, N. Wisitpongphan, F. Bai, P. Mudalige, V. Sadekar, “Broadcasting in VANET,” 2007 Mobile Networking for Vehicular Environments 11–11 May 2007, pp. 7–12.
[10]	Y. Zhang , J. Zhao and G. Cao, “On Scheduling Vehicle-Roadside Data Access” ACM Workshop on Vehicular Ad Hoc Networks (VANET), 2007. SESSION: Data access and security table of contents pp. 9–18.
[11]	O.K. Tonguz, N. Wisitpongphan, J.S. Parikh, Fan Bai, P. Mudalige, V.K. Sadekar “On the Bradcast Storm Problem in Ad Hoc Wireless Networks” Broadband Communications, Networks and Systems, 2006. BROADNETS 2006. 3rd International Conference on 1-5 Oct. 2006, pp. 1–11.
[12]	Tin-Yu Wu, Cheng-Chia Lai, and Han-Chieh Chao, “Efficient IEEE 802.11 Handoff Based on a Novel Geographical Fingerprint Scheme” Wireless Communications and Mobile Computing, Volume 6, Issue 1, Page 127-135, February 2006.
[13]	C. Wai, C. Shengwei, “Ad Hoc peer-to-peer network architecture for vehicle safety communications”, Communications Magazine, IEEE Volume 43, Issue 4, April 2005, pp. 100–107.
[14]	J. Ming-Fong, L. Wanjiun, “On Cooperative and Opportunistic Channel Access for Vehicle to Roadside (V2R) Communications”, Global Telecommunications Conference, 2008. IEEE GLOBECOM 2008. IEEE Nov. 30 2008-Dec. 4 2008, pp.1–5.
[15]	Chung-Sheng Li, Tak-Goa Tsuei, Han-Chieh Chao, "Evaluation of Contention-Based EDCA for IEEE 802.11e Wireless LAN", JIT Journal of Internet Technology, Oct. 2004. vol. 5, issue 4, pp. 429-434
[16]	蘇子翔, 胡大瀛, “Impact of Traffic Characteristics on Inter-Vehicle Communications”, 成功大學碩士畢業論文, 中華民國97年6月。
[17]	陳信菖, 陳彥文, “Study of Intelligent Routing Method for Advanced Vehicles in Safety Intelligent Transportation System”, 中央大學碩士畢業論文, 中華民國97年6月。
[18]	王國蔚, 吳中實, “無線區域網路802.11e EDCF之效能改善”, 中央大學碩士畢業論文, 中華民國93年6月。
[19]	A. Skordylis and N. Trigoni, “Delay-Bounded Routing in Vehicular Ad-Hoc Networks,” Proceedings of ACM International Conference on Mobile Ad Hoc Networking and Computing, Hong Kong, China, May 2008.
[20]	J. Luo and J. P. Hubaux, “A Survey of Inter-Vehicle Communications,” Technical Report IC, EPFL, Mar. 2004.
[21]	N. Wisitpongphan et al., “Broadcast Storm Mitigation Techniques in Vehicular Ad Hoc Networks,” IEEE Wireless Communication., vol. 14, no. 6, Dec. 2007, pp. 84-94, Dec. 2007.
[22]	Fan Yu, and S. Biswas, “Self-Configuring TDMA Protocols for Enhancing Vehicle Safety with DSRC Based Vehicle-to-Vehicle Communications,” Proceedings of the IEEE Journal on Selected Areas in Communications (IEEE JASC), vol. 25, iss. 8, pp. 1526-1537, October 2007.
[23]	Pan Li, Xiaoxia Huang and Yuguang Fang, "The Optimal Placement of Gateways in Vehicular Networks," IEEE Transactions on Vehicular Technology, Nov. 2007.
[24]	T. Fukuhara, T. Warabino, T. Ohseki, K. Saito, K. Sugiyama, T. Nishida, K. Eguchi. “Broadcast methods for inter-vehicle communications system”, Proceedings of IEEE Wireless Communications and Networking Conference, pp. 2252-2257, 2005.
[25]	P. Costa, D Frey, M. Migliavacca and L. Mottola, “Towards Lightweight Information Dissemination in Inter-Vehicular Networks,” Proceedings of the 3rd international workshop on Vehicular Ad Hoc networks, Sept. 2006.
[26]	J. Zhao and G. Cao, “VADD: Vehicle-Assisted Data Delivery in Vehicular Ad Hoc Networks,” Proceedings of IEEE International Conference on Computer Communications (INFOCOM 2006), Barcelona, Catalunya, Spain, April 2006.
[27]	Yuanguo Bi, Hai Zhao, Xuemin Shen, “A Directional Broadcast Protocol for Emergency Message Exchange in Inter-Vehicle Communications,” Communications, 2009. ICC 2009, Dresden, 14-18 June 2009.
[28]	Bi, Y., Cai, L. X., Shen, X., Zhao, H. “Efficient and Reliable Broadcast in Inter-Vehicle Communications Networks: A Cross Layer Approach,” Vehicular Technology, IEEE Transactions, Issue 99, page 1-1, March 2010.
[29]	W. Chen, R. K. Guha, J. K. Taek, J. Lee, and I. Y. Hsu, “A Survey and Challenges in Routing and Data Dissemination in Vehicular Ad-Hoc Networks,” Proceeding of IEEE International Conference on Vehicular Electronics and Safety (ICVES 2008), Columbus, USA, September 2008.
[30]	H. Wu, R. Fujimoto, R. Guensler, and Michael Hunter, "MDDV: a Mobility-Centric Data Dissemination Algorithm for Vehicular Networks," proceedings of the 1st ACM International Workshop on Vehicular Ad Hoc Networks (VANET 2004), pages 47-59, Philadelphia, PA, USA, October 2004.