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標題: IEEE 802.11無線網路之隨機掃描換手模擬
Handoff Simulation for Random Scan of IEEE 802.11 Wireless LAN
作者: 林忠成
Lin, Chung-Cheng
關鍵字: Wireless Local Area Networks (WLANs);無線區域網路;Handoff;Channel Scan;Random Scan;換手;通道掃描;隨機掃描
出版社: 電機工程學系所
引用: [1] 梁世聰,吳忠益,翁明儀,“支援IEEE 802.11基礎架構式無線區域網路模擬器之設計與建置”,台北市立師範學院,大葉大學,2004. [2] 賴彥呈,“IEEE 802.11無線網路通道品質預測之漫遊決策”,國立中興大學,2006. [3] 柯志亨,“計算機網路實驗--以NS2模擬工具實作”,學貫行銷, 2007. [4] 盧彥霖,“IEEE 802.11 無線網路以競爭視窗為基準之漫遊決策”,國立中興大學,2007. [5] 黃昭憲,“IEEE 802.11 無線網路以工作站判決之漫遊決策”,國立中興大學,2008. [6] 張詠盛,“IEEE 802.11 無線網路漫遊之隨機掃描”,國立中興大學,2009. [7] 辛偉豪,“IEEE 802.11 無線網路漫遊中隨機掃描之改良”,國立中興大學,2010. [8] “ IEEE 802.11 WG, Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specification,” Standard, IEEE, 1999. [9] Giuseppe Bianchi, “ Performance Analysis of the IEEE 802.11 Distributed Coordination Function”, IEEE Journal on Selected Areas in Communications, vol. 18, pp.535-547, 2000. [10] Fred Halsall, “Computer Networks and The Internet, 5/e”,Addison-Wesley Publishing Company, 2005. [11] Kevin Fall and Kannan Varadhan, “The ns Manual ”, 2006. [12] Matthew Gast, “ 802.11 Wireless Networks : The Definitive Guide, 2/e ” ,O’Reilly , 2006. [13] Haitao Wu, Kun Tan, Yongguang Zhang, “Proactive Scan: Fast Handoff with Smart Triggers for 802.11 Wireless LAN”, Proc. 26th IEEE International Conference on Computer Communications, pp.749-757, 2007. [14] Larry L. Peterson, Bruce S. Davie, “Computer Networks: A Systems Approach, 4/e ” , Morgan Kaufmann Publishers, 2007. [15] Yuh-Shyan Chen, Ming-Chin Chuang, and Chung-Kai Chen, “DeuceScan: Deuce-Based Fast Handoff Schemein IEEE 802.11 Wireless Networks”, IEEE Transactions on Vehicular Technology, vol. 57, pp.1126-1141, 2008. [16] “Tutorial for the Network Simulator ns”, [17] “NS by Example”, [18] “The ns Manual”, [19] “AWK Tutorial Guide, version 2.2”,
近年來隨著IEEE 802.11無線網路的發展,目前搭載無線上網功能的行動裝置已經非常普及。透過網路存取點(AP,Access Point)在空間上的建置所形成涵蓋範圍廣闊的網路,讓移動式的無線上網裝置在網路中往返移動時,可以藉由這個擴充網路從一個存取點漫遊至下一個存取點以完成無間縫的漫遊。而整個無線漫遊所造成的時間延遲可區分為三個部分:掃描延遲、身份認證延遲、和重新連結延遲。漫遊延遲中則以掃描延遲佔據最大的時間比例,所以漫遊延遲如果愈長,服務中斷的時間也會愈長。
隨機掃描(Random Scan)為一個減少IEEE 802.11無線網路漫遊所造成服務中斷的機制,此機制將指標信號間隔時間(Beacon Interval)切割成三個區段(Section),在每次的指標信號間隔時間中,只針對一個區段進行掃描,剩下的時間可繼續正常的傳輸,以降低服務被中斷的時間。隨機掃描開啟時,會隨機產生通道順序(Channel Sequence)與區段順序(Section Sequence)來掃描通道,工作站(Station)就根據產生的通道順序與區段順序,依排程切換至目標通道來搜尋存取點。

With the development of IEEE 802.11 wireless network in recent years, mobile devices equipped with wireless network capability have become very popular. The wide deployment of wireless network access points (AP) forms a wireless network with very large coverage. To enable a mobile device connecting to the wireless network uninterruptedly, we need fast and reliable handoff procedures between AP's. The handoff delay can be divided into three parts: channel scan, authentication, and re-association. Among these, the channel scan time accounts for the largest proportion of handoff time.
Random scan is a channel scan method in IEEE 802.11 wireless networks design to reduce the channel scan time. It divides a beacon interval into three sections. In each beacon interval, one section in randomly selected and a randomly selected channel is scanned for available AP's. Normal transmission can be conducted in the remaining sections. It takes three beacon intervals to scan all the sections. The sequences for channels and sections are randomly generated. Each station switches to the target channel according to the sequences.
To extend the studies of random scan, this thesis focuses on handoff simulation of random scan and passive scan and compares the differences between the two. To alleviate the problem that scanning time may not be enough in random scan when the moving speed is high, we add a threshold to activate channel scan before handoff is required. In simulations, we find that random scan can reliably find suitable AP to switch and significantly shorten the channel scan time at various speeds.
其他識別: U0005-2707201117483200
Appears in Collections:電機工程學系所

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