現行用於無線Ad Hoc網路的MAC（Medium Access Control）協定採用IEEE 802.11的標準。而IEEE 802.11的CSMA/CA（Carrier Sense Multiple Access with Collision Avoidance）在MH（Mobile Host）競爭傳輸媒介發生碰撞、重傳時，Binary Exponential Backoff演算法會產生很大的Backoff時間，造成封包的延遲（Delay）和延遲變化（Jitter）大幅增加，也就限制了多媒體資料流的應用趨勢。因此，後續有很多研究用於無線Ad Hoc網路且具有優先權機制的MAC協定，至今仍然沒有可以提供QoS（Quality of Service）保證的優先權機制標準存在。
本論文提出ㄧ套適用於無線Ad Hoc網路且具有優先權機制的MAC協定，不僅可以達成差別式服務，而且能夠免除既有方法的缺點。我們所提出的JMAC機制是以雜訊為基礎（Jamming-based）的媒體競爭策略，其架構的核心在於發送Jamming Noise干擾傳輸媒體的觀念，送出Jamming Noise最長的MH將贏得媒體使用權，可以傳送資料訊框（Frame）。再者，JMAC機制中動態調整優先權的設計使得每一個MH根據網路上的競爭和壅塞狀況來動態調整自身的競爭優先權和Jamming Noise的長度，以提供不同優先權等級的QoS保證，並防止低優先權資料流的Starvation與網路Deadlock的產生。所以，整個JAMC機制涵蓋了三大功能：Collision Avoidance、Starvation Prevention和Deadlock Prevention。
最後我們與制定中的IEEE 802.11e draft 的EDCF（Enhanced DCF）和其他論文做比較與分析；透過NS-2模擬的方式，驗證我們的機制確實可以給予不同優先權不同的服務品質保證。

IEEE 802.11 has become the standard of medium access control (MAC) in wireless ad hoc networks. However, due to the embedded binary exponential backoff algorithm, the packet delay and jitter incurred by access collisions and frame retransmissions may grow drastically. The lack of time-constraint considerations in IEEE 802.11 makes it very difficult to provide QoS (Quality of Service) guarantees for multimedia services. Therefore, a lot of research works focusing on priority-based MAC protocols for wireless ad hoc networks have been proposed. Yet, no standards come out until now.
This thesis presents a priority-based MAC scheme in wireless ad hoc networks, which not only provides differentiated services, but also improves the QoS limitations of the previously proposed schemes. The main idea of the proposed JMAC (jamming-based MAC) mechanism is that traffic flows with different priorities can be differentiated by transmitting jamming noises of different lengths to interfere with one another. The one with the longest length of jamming noise can start data transmission. Besides, in our design, priority can be dynamically adjusted to allow each MH to change its contention priority and the length of jamming noise in accordance with network congestions. To implement the proposed JMAC, three modules are developed in this thesis: Collision Avoidance, Starvation Prevention, and Deadlock Prevention.
For the purpose of evaluation, we perform simulations on the well-known network simulator, NS-2. Our scheme is compared with the EDCF (enhanced distributed coordination function) of IEEE 802.11e（draft）and one of the existing works. The simulation results demonstrate the effectiveness and superiority of our scheme.

目 錄

第一章 導論………………………………………………………………………1
1.1 研究動機……………………………………………………………………1
1.2 研究方向與模擬……………………………………………………………2
1.3 章節介紹……………………………………………………………………4

第二章 Ad Hoc無線網路背景與相關研究…………………………………5
2.1 IEEE 802.11 MAC機制簡介……………………………………………6
2.2 Ad Hoc網路的優先權機制……………………………………………7
2.2.1針對Interframe Space的相關研究………………………………8
2.2.2針對Backoff Algorithm的相關研究…………………………10
2.2.3其他改進MAC效能的方法……………………………………12
2.2.3.1 802.11e EDCF……………………………………………12
2.2.3.2 Jamming-based 重傳機制………………………………14
2.3各種改善Wireless MAC Layer效能的方法比較………………… 15
2.4本論文的動態調整競爭優先權機制……………………………… 17

第三章 以雜訊為基礎的媒體競爭策略……………………………………18
3.1以雜訊為基礎並具有動態調整競爭優先權的MAC策略……18
3.1.1系統架構………………………………………………...….18
3.1.2機制運作流程………………………………………………………23
3.1.2.1 Deadlock Prevention………………………………………27
3.1.2.2 Starvation Prevention……………………….……….27
3.1.2.3 Collision Avoidance……….…………….………….28
3.1.3機制運作實例………………………………………………………29
3.2演算法………………………………………………………………………30

第四章 模擬分析及結果量測…………………………………………………33
4.1模擬環境與網路拓樸…………………………………………………33
4.2模擬結果與分析討論…………………………………………………37
4.2.1 Differentiate並保障不同優先權的QoS……………………………37
4.2.2 與Chen 機制比較…………………………………………………45
4.2.3 與EDCF機制比較…………………………………………………52

第五章 結論與未來工作方向…………………………………………………55
5.1 結論………………………………………………………………………55
5.2未來工作方向………………………………………………………………56

Reference……………………………………………………………………………58
Index…………………………………………………………………………………61

圖表目錄

圖 2.1 IEEE802.11競爭存取的基本架構……………………………………………6
圖 2.2 CW值增加方式………………………………………………………………7
圖 2.3 DDRR機制……………………………………………………………………9
圖 2.4 Chi-Hsiang Yeh et al.機制示意圖…………………………………………11
圖2.5 Chi-Hsiang Yeh et al.機制避免碰撞方法…………………………………12
圖 2.6 EDCF中新增的QoS欄位……………………………………………………13
圖 2.7 IEEE 802.11e的AC分類……………………………………………………13
圖 2.8 jamming-based 重傳機制競爭channel示意圖………………………………14
圖 2.9 jamming-based 重傳機制流程圖……………………………………………15
圖 3.1計算Lcf的法則………………………………………………………………21
圖3.2本論文JMAC機制運作示意圖……………………………………………22
圖 3.3所有MH皆剛加入此Ad Hoc網路中………………………………………23
圖 3.4所有MH皆已在此Ad Hoc網路中競爭一回合以上………………………23
圖 3.5有新MH加入此一Ad Hoc網路中…………………………………………24
圖 3.6本論文機制流程圖…………………………………………………………26
圖3.7 JMAC媒體競爭機制範例…………………………………………………29
圖 4.1模擬網路拓樸………………………………………………………………34
圖4.2 NS-2無線Ad hoc網路類別架構…………………………………………36
圖4.3 不同優先權的競爭Flow數與平均競爭成功百分比關係…………………37
圖4.4 不同優先權的Packet Sending Rate與Packet Drop Ratio關係…………….38
圖4.5 Starvation Prevention機制下的Packet Drop Ratio……………………………39
圖4.6 Starvation Prevention機制下的競爭Flow數與Medium Access Delay關係…41
圖4.7 SP機制下的競爭Packet Sizes與Medium Access Delay關係………………42
圖4.8 SP機制下的封包產生速率與Waiting Delay關係…………………………44
圖4.9（a） Packet Sizes等於100~1000 Bytes時，JMAC與Chen機制平均競爭失敗百分比的比較………………………………………………………46
圖4.9（b） Packet Sizes等於100 Bytes時，JMAC與Chen機制的平均競爭失敗百分比的比較……………………………………………………………48
圖4.10（a） Packet Sizes為100~1000 Bytes時，Chen機制與JMAC機制的競爭Flow 數與平均Throughput關係……………………………………………49
圖4.10（b）Packet Sizes等於100 Bytes時，JMAC機制和Chen機制的競爭Flow數與平均Throughput關係……………………………………………51
圖4.11 JMAC機制和EDCF的競爭Flow數與平均Throughput關係………………53


表2.1 8種Priority Mapping到4種AC………………………………………13
表2.2各種改進MAC 競爭機制的比較…………………………………………16
表 4.1模擬環境參數………………………………………………………………34
表 4.2 EDCF參數設定……………………………………………………………52

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