摘要

針對目前 IEEE 802.11 a/b/g 無線系統皆以碰撞避免式載波偵測多重存取(carrier sense multiple access with collision avoidance; CSMA/CA) 以競爭為基礎，其並無法提供完整服務品質(quality of service; QoS)的保證，IEEE因而制定802.11e標準針對中樞協調功能(pointer coordination function; PCF)及分散式協調功能(distributed coordination function; DCF)環境分別做不同的媒介存取控制層協定(medium access control; MAC)設計以提供QoS保證。但在無線的環境中每個節點的執行速率與頻寬隨時都在改變，因此要確實執行QoS保證仍有許多困難，本論文希望能針對無線環境中可變頻寬的特性來加強QoS的保證。
本論文，在IEEE 802.11e EDCA mode多重傳送速率下的無線網路基礎架構中，提出一個適應性速率控制(adaptive rate control algorithm; ARCA)方法，改善因為頻寬與速率變動而下降的產能(throughput) 、降低每個封包碰撞率(per-packet collision rate)及封包丟棄率(dropping rate)，更有效率的使用無線區域網路(wireless local area network；WLAN)資源。ARCA利用頻寬因數(bandwidth factor)與優先權表格(priority table)動態調整EDCA的參數仲裁訊框間間隔(arbitration inter-frame space；AIFS)、競爭視窗(contention window; CW)、持續因數(persistence factor; PF) 等，配合實體層速率上升或下降來組合變化這些參數，來提高整個系統工作效能。使得實體層速率較高之工作站(station; STA)不會受到因通道狀態改變而有較低實體層速率之STA影響。透過模擬的方式，將我們所提出的方法與IEEE 802.11e標準互相比較，從模擬結果顯示，ARCA確實能比IEEE 802.11提供更好的產能。

Abstract
All based on carrier sense multiple access with collision avoidance (CSMA/CA) contention base to IEEE 802.11 a/b/g wireless system at present. It is unable to offer the assurance of intact quality of service (QoS) , therefore IEEE makes 802.11e standard to offer QoS. IEEE 802.11e does different medium access control (MAC) layer to design separately to pointer coordination function (PCF) and distributed coordination function (DCF). But each nodal execution speed with bandwidth to change at any time among wireless environment, so should really carry out QoS and guarantee that there are a lot of difficulties. This thesis hopes to strengthen the assurance of QoS to the variable and bandwidth characteristic in the wireless environment.
This paper proposes an adaptive rate control algorithm (ARCA) to improve throughput, collision rate and drop rate of each packet in the IEEE 802.11e EDCA mode multi-rate infrastructure wireless networks. It uses more efficient wireless LAN resources. ARCA utilizes the parameter of bandwidth factor and priority table dynamically to adjust the parameter of arbitration inter-frame space (AIFS), contention window (CW) , persistence factor (PF) of EDCA. These parameters are adjusted by ARCA to improve the efficiency of the whole system according to the rising or falling of the data rate in physical layer. Making the 802.11e high data rate of station (STA) don’t be influenced the lower data rate of STA because the channel status changed. By way of simulating, ARCA compares with 802.11e standard. It can offer better throughput than 802.11e.

目次
中文摘要……………...…………………………...........…......iv
英文摘要 ……………...…………………………...........….......v
圖表索引 ……………...…………………………...........…......ix

第一章 緒論 ……………………………………………….……...…..1
1.1 簡介 …….……………...………………………………………….1
1.2 研究動機與目的……………………………….………..……….. 3
1.3 章節概要…..……..……………………………….……..….….…5
第二章 具服務品質保證之IEEE 802.11e…….…...............…6
2.1 IEEE 802.11e的簡介 .…...……...………….…..…..….…..………6
2.2 IEEE 802.11e的MAC層…..…………………….….....………...11
2.2.1 EDCA參數描述……………...……………………….…..12
2.2.2 EDCA運作描述……………...……………………….…..14
2.2.3 HCCA參數描述…...………...………………….…….…..17
2.2.4 HCCA運作描述…………………………………………..21
2.2.5 CAP與CFP的描述……………………………………….23
2.2.6受控制的競爭機制(CC mechanism)……..…..…………...25

第三章 系統架構與ARCA演算法 ……...……………….…...…26
3.1系統架構……..…………………...…………………….…….….. 26
3.2 ARCA演算法…...…...…….……………………..….…..….…… 27
3.3演算法流程…………………………………………...…………..32
第四章 系統模擬與分析 …………...………………………….….34
4.1 模擬架構與參數………..……….....……………………….…... 34
4.2 效能評估項目….…...………….………………….……………. 37
4.2.1產能(throughput)……………...…………...………….….. 37
4.2.2損失的產能(depreciation of throughput) …...………….…37
4.2.3每個封包的平均碰撞率(per-packet collision rate)…...…. 37
4.2.4平均丟棄封包率(drop rate)…...………...….……………..38
4.2.5封包佇列在緩衝器(queued packets in buffer)……………38
4.3 結果分析與比較 ………………………………...……………... 39
第五章 結論 ……………………………………..………...………...51
參考文獻 …………………………………………………..……….…52













圖表索引
圖2-1 MAC層架構…………………………….………...………………7
圖2-2 細分TID 欄位…………………………...………………………9
圖2-3 MAC層的QoS架構…….…….…………….….…………….…10
圖2-4 EDCA序列模型……………………….……..……………….…14
圖2-5 EDCA時間關係………….………………………….…......……15
圖2-6 HCF時間關係…………………………...………………………22
圖2-7 Superframe的架構………………………….…….…….….……23
圖2-8 Polled TXOP…………………….……………………………….23
圖3-1 ARCA系統架構……………………..………..….……………...27
圖3-2 CAMA/CA流程………………………...…….…………………28
圖3-3 ARCA演算法流程………………………………………....……33
圖4-1 ARCA演算法之系統架構……………...………………...……..35
圖4-2 ARCA與EDCA之總產能比較……………………….………...41
圖4-3 ARCA與EDCA之總產能比例比較……………………….…...41
圖4-4 ARCA與EDCA之STAstationary與STAmove產能比較……………42
圖4-5 ARCA與EDCA之STAmove產能比較……….…….……………42
圖4-6 ARCA與EDCA之產能比較……..….……………………….…43
圖4-7 ARCA與EDCA之每個封包碰撞率比較….…..………………43
圖4-8 ARCA與EDCA之封包丟棄率比較………..…………...…...…44
圖4-9 ARCA與EDCA之封包佇列在緩衝器比較…….……...………44
圖4-10 ARCA與EDCA之總產能比較………………….…...……......46
圖4-11 ARCA與EDCA之STAstationary與STAmove產能比較…………..46
圖4-12 ARCA與EDCA之產能比較………………..…………….…..47
圖4-13 ARCA與EDCA之每個封包碰撞率比較……………………..47
圖4-14ARCA與EDCA之封包丟棄率比較...………..………….……48
圖4-15 ARCA與EDCA之封包佇列在緩衝器比較…………..………48
圖4-16 ARCA與EDCA之總產能比較…………..…..….………….…49
圖4-17 ARCA與EDCA之總產能比較………..……..….………….…50
表2.1 IEEE 802.11e MAC 封包格式…………………...……...……….8
表2.2 IEEE 802.11e MAC封包之QoS 控制欄位………….…………..8
表2.3 QoS 控制欄位中之TID 欄位…..………………......….………..8
表2.4 IEEE 802.11e Priority與Access Category對應表………….……9
表2.5 EDCA參數設定項目欄位………….……………..…………….12
表2.6 EDCA參數項目中之AC欄位……………………………...…. 12
表2.7 EDCA參數項目中之AC參數記錄欄位...…………………...…12
表2.8 EDCA參數項目中之ACI/AIFSN 欄位...………....………….. 12
表2.9 EDCA參數項目中之ACI to AC coding...…………..…………. 12
表2.10 EDCA參數項目中之ECWmin/ECWmax欄位......………………13
表2.11 Default EDCA 參數設定..………………………….…...……..14
表2.12 Beacon訊框中之Traffic Specification element格式…..…...…17
表2.13 Traffic Specification element中之TS Info 欄位.……………. 17
表2.14 TS Info 欄位中之Direction field encoding.……………….…. 17
表2.15 TS Info 欄位中之Access Policy....…….…………………...…18
表2.16 TS Info 欄位中之TSInfo Ack Policy field encodin………….. 18
表2.17 IEEE 802.11e Nominal MSDU Size 欄位…..…….………….. 18
表3.1 ARCA演算法頻寬需求表....……...……….………..…………..30
表3.2 AC對應r之頻寬需求表……………………..……….…………30
表3.3 競爭參數表………...............................................................……31
表4.1 MAC參數...………..…………………………………………….35
表4.2 802.11e 標準之競爭參數...……………………………………..35
表4.3 ARCA競爭參數...……………………………………….…....…36
表4.4 ARCA演算法模擬參照表………….…….……………………..36

參考文獻
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