Please use this identifier to cite or link to this item: http://hdl.handle.net/11455/8109
DC FieldValueLanguage
dc.contributor.advisor廖俊睿zh_TW
dc.contributor.author施金山zh_TW
dc.date2003zh_TW
dc.date.accessioned2014-06-06T06:41:01Z-
dc.date.available2014-06-06T06:41:01Z-
dc.identifier.urihttp://hdl.handle.net/11455/8109-
dc.description.abstract摘要 802.11無線區域網路可大致分為無基礎架構網路與有基礎架構網路,無基礎架構網路指的是基本服務區內沒有擷取點與其他的有線或無線區域網路聯結,反之則為有基礎架構的網路。在802.11無線區域網路中的工作站必須經由802.11 媒介存取控制協定來取得無線傳輸媒介的傳送權以傳送資料,802.11 媒介存取控制協定包含有分散式協調機制與集中式協調機制。分散式協調機制就是CSMA/CA機制,工作站必須感測傳輸媒介閒置了一段特定時間後才能傳送資料,每個工作站都有相同的機會競爭到傳輸媒介的傳送權。而集中式協調機制則是由一個稱為集中協調者的裝置經由輪詢的方式決定那個工作站何時有權利傳送資料。 分散式協調機制並不能提供工作站服務品質保證,所以有許多學者提出了加強分散式協調機制服務品質保證的方法,802.11也提出了加強其原本媒介存取協定服務品質功能的協調機制。802.11提出的新的協調機制分別針對分散式協調機制與集中式協調機制機制做改良,其中針對分散式協調機制改良的部分(稱為增強分散式協調機制)容易因為工作站數目變多而嚴重的降低其效能,所以我們使用名為適應性增強分散式協調機制的方法改良增強分散式協調機制使得工作站可以視網路情況調整其媒介存取控制的參數,如此可以使得增強分散式協調機制的效能獲得顯著的改善。我們利用NS2實際的模擬來比較適應性增強分散式協調機制與增強分散式協調機制的效能差異。zh_TW
dc.description.abstractAbstract The IEEE 802.11 Wireless Local Network (WLAN) specification defines two ways to configure a wireless network: ad-hoc mode and infrastructure mode. Ad-hoc networks do not use an access coordinator to connect wireless stations to a Distribution System (DS) but infrastructure networks do. Wireless stations in IEEE 802.11 WLAN should use IEEE 802.11 Medium Access Control (MAC) protocol to access wireless medium to transfer data. IEEE 802.11 MAC protocol incorporates two access methods: Distributed Coordination Function (DCF) and Point Coordination Function (PCF). DCF is based on the Carrier Sense Multiple Access/Collision Avoidance (CSMA/CA) protocol. In this mode, a station must sense the medium before sending a packet. If the medium is found idle for a specific time then it can transmit a packet. PCF uses a Point Coordinator (PC) to determine which STA currently has the right to transmit. The operation is essentially that of polling, with the PC performing the role of the polling master. DCF can not provide any Quality of Service (QoS), so there are many medium access schemes proposed for IEEE 802.11 WLAN to provide QoS. The IEEE 802.11 is currently working on the support of QoS in a new standard, called IEEE 802.11e. A new access method called Hybrid Coordination Function (HCF) is introduced. It is a queue-based differentiation that uses both DCF and PCF enhancements. One of the main problems of Enhanced DCF is the static reset of the Contention Window (CW) which decreases the throughput performance and increases the collision rate especially at high load conditions. We use a mechanism named Adaptive Enhanced Distributed Coordination Function (AEDCF) that stations can dynamically adjust their CW depending on traffic load, so the collision rate will increase more slowly. We use Network Simulator Version 2 (NS2) to simulate AEDCF and EDCF, and results show that AEDCF outperforms the basic EDCF especially at high load conditions.en_US
dc.description.tableofcontents摘要……………………………………………………………...…………i ABSTRACT……………………...…………………………………….…iii 致謝………………………………………………………………………...v 目錄………………………………………………………………………..vi 圖目錄……………………………………………………………………..ix 表目錄…………………………………………………………………..…xi 第一章 緒論……………………………………………………………….1 1.1動機與目的………………………………………………………….1 1.2 論文架構……………………………………………………………3 第二章 802.11無線區域網路架構………………………………………..4 2.1 無線區域網路硬體架構……………………………………………8 2.2 無線區域網路軟體架構…………………………………………..12 2.3 總結………………………………………………………………..17 第三章 802.11 MAC協定……………………………………………….18 3.1 分散式協調機制…………………………………………………..19 3.1.1 訊框間隔……………………………………………………...20 3.1.2 衝撞偵測與虛擬載波偵測…………………………………...22 3.1.3 退後機制……………………………………………………...24 3.2集中式協調機制…………………………………………………...26 3.2.1 免競爭週期的結構與時序…………………………………...28 3.2.2 PCF機制的運作程序…………………………………………31 3.2.3 PCF傳輸程序…………………………………………………33 3.2.4 輪詢名單的建立與維護……………………………………...38 3.3 總結………………………………………………………………..39 第四章 加強802.11服務品質保證機制介紹…………………………..41 4.1 有關加強802.11無線區域網路服務品質的機制……………….41 4.1.1 Assured Rate MAC Extension……………………….…………42 4.1.2 Differentiation Mechanisms…………………………………...44 4.1.3 Priority-Based Contention Control Scheme…………………...46 4.2 802.11e的服務品質保證機制……………………………………..50 4.2.1 增強分散式協調機制(EDCF)………………………………..51 4.2.2 改良後的PCF機制(HCF controlled channel access)…….....53 4.2.3 受控制的競爭機制(Controlled contention mechanism,CC mechanism)……..…………………………………………….55 4.3 總結………………………………………………………………..56 第五章 適應性EDCF介紹與模擬結果………...………………………58 5.1 適應性EDCF……………………………………………………...58 5.2 模擬平台介紹……………………………………………………..62 5.3 模擬結果討論……………………………………………………..63 5.3.1 更新週期的影響……………………………………………...63 5.3.2 平滑因子的影響……………………………………………...68 5.3.3 MF上限值的影響……………………………………………..70 5.3.4 AEDCF效能評估……………………………………………...72 5.4 總結………………………………………………………………..79 第六章 結論與未來展望………………………………………………...81 參考文獻………………………………………………………………….83 圖目錄 圖2-1無線網路硬體架構組成元件...........................................................11 圖2-2 無線區域網路與其他IEEE802區域網路的連結..........................11 圖2-3 無線區域網路軟體服務.................................................................13 圖3-1 MAC架構表示圖.............................................................................19 圖3-2分散式協調機制...............................................................................20 圖3-3 競爭視窗值增加方式.....................................................................25 圖3-4 免競爭週期與競爭週期的交替.....................................................28 圖3-5 Beacon間隔與免競爭週期範例......................................................30 圖3-6延遲傳送之Beacon訊框與縮短之免競爭週期範例......................31 圖3-7免競爭週期中訊框傳送的範例.......................................................34 圖4-1 ARME機制的操作模式..................................................................42 圖4-2 Token bucket理論示意圖................................................................43 圖4-3 Different DIFS..................................................................................45 圖4-4 RTS訊框的比較...............................................................................47 圖4-5 EDCF與DCF架構比較圖...............................................................52 圖4-6 IEEE 802.11e中訊框間隔的關係...................................................52 圖4-7 一個802.11e超級訊框....................................................................54 圖5-1 模擬的拓樸結構.............................................................................63 圖5-2 更新週期對於平均傳輸延遲時間的影響.....................................66 圖5-3更新週期對於平均傳輸頻寬的影響...............................................66 圖5-4平滑因子對於平均傳輸延遲時間的影響.......................................68 圖5-5平滑因子對於平均傳輸頻寬的影響...............................................69 圖5-6 語音資料傳輸時間延遲比較.........................................................73 圖5-7視訊資料傳輸時間延遲比較...........................................................73 圖5-8背景處理資料傳輸時間延遲比較...................................................74 圖5-9 媒介使用率比較.............................................................................74 圖5-10 碰撞率比較...................................................................................75 圖5-11 平均傳輸頻寬比較.......................................................................76 圖5-12 頻寬增益比...................................................................................77 圖5-13 語音資料傳輸時間延遲的標準差分佈.......................................78 圖5-14視訊資料傳輸時間延遲的標準差.................................................78 圖5-15背景處理資料傳輸時間延遲的標準差.........................................79 表目錄 表5-1 資料的網路參數.............................................................................64 表5-2 PHY層的網路參數..........................................................................65 表5-3 MF上限值的影響............................................................................70zh_TW
dc.language.isoen_USzh_TW
dc.publisher電機工程學系zh_TW
dc.subjectWLANen_US
dc.subject802.11無線區域網路zh_TW
dc.subjectad-hoc networksen_US
dc.subjectinfrastructure networksen_US
dc.subjectmedium access controlen_US
dc.subjectdistributed coordination functionen_US
dc.subjectpoint coordination functionen_US
dc.subjectQuality of Serviceen_US
dc.subject無基礎架構網路zh_TW
dc.subject有基礎架構網路zh_TW
dc.subject媒介存取控制zh_TW
dc.subject分散式協調機制zh_TW
dc.subject集中式協調機制zh_TW
dc.subject服務品質保證zh_TW
dc.title802.11無線區域網路之適應性增強分散式協調機制zh_TW
dc.titleAdaptive Enhanced Distributed Coordination Function in 802.11 Wireless LANen_US
dc.typeThesis and Dissertationzh_TW
item.languageiso639-1en_US-
item.openairetypeThesis and Dissertation-
item.cerifentitytypePublications-
item.grantfulltextnone-
item.fulltextno fulltext-
item.openairecristypehttp://purl.org/coar/resource_type/c_18cf-
Appears in Collections:電機工程學系所
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