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標題: IEEE 802.11 無線網路以工作站判決之漫遊決策
IEEE 802.11 Wireless LAN Roaming Based on Stations
作者: 黃昭憲
Huang, Chao-Hsien
關鍵字: 802.11 wireless local area network;802.11無線網路;roaming decision;collision rate;漫遊決策;碰撞率
出版社: 電機工程學系所
引用: [1] 賴彥呈, “IEEE 802.11 Wireless LAN Roaming Based on Channel Quality Estimation ,”國立中興大學,2006. . [2] C. Siva Ram Murthy and B. S. Manoj,“Ad Hoc Wireless Networks Architectures and Protocols,” Prentice Hall, 2004. [3] Larry L. Peterson and Bruce S. Davie, “Computer Networks-a systems approach third edition, ”Morgan Kaufmann , 2003. [4] Fred Halsall ,“ Data Communications, Computer Networks and Open Systems,” 4th Ed , Addison-Wesley ,1996. [5] Mattbew S. Gast ,“ 802.11 Wireless Networks,” O’Reilly , 2006. [6] Kevin Fall and Kannan Varadhan, “The ns Manual”, 2006. [7] IEEE 802.11 WG, Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specification, Standard, IEEE, 1999. [8] Shwar Ramani, Stefan Savage , “ SyncScan:Practical Fast Handoff for 802.11 Infrastructure Networks,” Proceeding of the IEEE infocom Conference, Miami, FL, vol.1, pp.675-684, 2005. [9] Yang Xiao, “Concatenation and Piggyback Mechanisms for the IEEE 802.11 MAC,” Wireless Communications and Networking Conference, vol. 3, pp.1642-1647, 2004. [10] Yang Xiao,“ Performance Analysis of Priority Schemes for IEEE 802.11 and IEEE 802.11e Wireless LANs,” IEEE Transactions on Wireless Communications, vol. 4, pp.1506-1515, 2005. [11] Hongqiang Zhai, Xiang Chen and Yuguang Fang,“ How Well Can the IEEE 802.11 Wireless LAN Support Quality of Service,” IEEE Transactions on Wireless Communications, vol. 4, pp.3084 – 3094, 2005. [12] G. Bianchi, “Performance Analysis of the IEEE 802.11 Distributed Coordination Function,” IEEE Journal on Selected Areas in Communications, vol. 18, pp.535-547, 2000. [13] Ping-Jung Huang, Yu-Chee Tseng and Kun-Cheng Tsai, “A Fast Handoff Mechanism for IEEE 802.11 and IAPP Networks”, IEEE Vehicular Technology Conference, pp.966 – 970, 2006. [14] Seongkwan Kim, Sunghyun Choi, Se-kyu Park, Jaehwan Lee and Sungmann Kim, “An Empirical Measurements-based Analysis of Public WLAN Handoff Operations,” First International Conference on Communication System Software and Middleware, pp.1-6, 2006. [15] Jung-Ryun Lee, Sang-Wook Kwon, and Dong-Ho Cho, “Adaptive Beacon Listening Protocol for a TCP Connection in Slow-Start Phase in WLAN,” IEEE Communications Letters, vol. 9, pp.853-855, 2005. [16] “AWK Tutorial Guide, version 2.2”,,中央研究院計算中心. [17] “Tutorial for the Network Simulator ns”, [18] Ns version 1 -LBNL Network Simulator. [19] 戴證倫, “IEEE802.11 Wireliss LAN Roaming Based on Congestioin Rate,”國立中興大學,2007. [20] 盧彥霖, “IEEE 802.11 Wireless LAN Handoff Decision based on Contention Window,”國立中興大學,2007. [21] 柯志亨, “計算機網路實驗,” 學貫行銷股份有限公司, 2007. [22] D-link團隊, “無線區域網路技術白皮書,” 松崗股份有限公司, 2005.
在IEEE 802.11無線區域網路的有基礎架構模式中,以存取點(Access Point , AP)用來連接無線網路與有線網路,工作站必須先跟AP註冊才能透過AP連接有線網路。在原本802.11的漫遊決策機制中,工作站僅會根據AP訊號強度的大小來決定漫遊的時機。當目前連結的AP訊號衰減到臨界值時,工作站會開始掃描尋找其它AP的訊號,而且其它AP的訊號強度也要超過臨界值才會確定漫遊的目標。但是訊號最強但範圍內通道情況為忙碌的AP,可能因碰撞率的增加而使連線品質不佳。所以有學者提出一種新的漫遊決策機制,稱為「碰撞率為基準之漫遊決策機制」,將碰撞率納入考量,由AP搜集工作站的碰撞率大小做為漫遊判斷的依據。

In the infrastructure mode of IEEE 802.11 wireless local area network, an access point (AP) is used to connect a wireless network to a wired network. A wireless station needs to associate with an AP before it can connect to a wired network. In 802.11 standard, when the signal strength of the registered AP falls below a threshold, the station begins to scan for signals from other AP's. If the signal strength from one of the other AP's is above a threshold, the station then switches to the new AP by re-associating with the new AP and de-associating with the old AP. However, an AP with large signal strength may have a high collision rate within its reception area. In other words, associating with this AP may not yield good connection quality because of the high collision rate. Therefore, our group has proposed a new roaming mechanism called “collision-rate-based roaming mechanism”. This mechanism used collision rate to decide when to switch from one AP to another AP. In this mechanism, an AP collects collision rate from all the stations associated with it and distributed the collision rate information back to stations. The stations can then use the information to decide whether to switch or not.
Based on collision-rate-based roaming mechanism, this thesis investigated in two new directions. The first direction is to speed up the roaming time. Our approach is to reduce the collision rate threshold and make the AP search start earlier. The second direction is that instead of collecting and distributing collision rate by AP, a station uses its own collision rate to decide whether to switch or not. This approach can greatly simplify the whole roaming process. Finally, we did simulation to verify the above two new methods.
其他識別: U0005-3107200823433200
Appears in Collections:電機工程學系所

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