本論文在Machine to Machine (M2M)的通訊環境中根據802.11ah提出一個動態時槽分配機制(Dynamic Slot Allocation Scheme, DSAS)，本機制可以有效使用無線資源以達成減少Machines大量競爭的目的，我們在DSAS中設計兩組臨界值，分別用來判斷每個Machine睡眠時間的長短和每個時槽(Slot)的壅塞程度，我們使用睡眠時間計算第一組臨界值，用來將Machine分成三種睡眠等級(High、Average和Low)，並使用競爭成功的Machines的平均退避時間來計算第二組臨界值，用來將所有Slots分成三種壅塞等級(High、Average和Low)，本論文的創新在於我們將原本使用較壅塞Slot且睡眠時間較短的Machines分配至較閒置的Slots，並將原本使用較閒置Slot且睡眠時間較長的Machines分配至較壅塞的Slots，另外，為了避免壅塞Slots內的Machines全部移至閒置的Slot，當Slot的壅塞等級為Average或是Machines的睡眠等級為Average時，Machines所使用的Slots不做任何調整。為了分析本論文所提出的DSAS並與802.11ah的Slot分配機制做比較，我們修改NS-3的Wi-Fi模組進行模擬，在模擬中我們逐步增加Machines的數量並讓每個Machines隨機產生不同的睡眠時間，模擬結果顯示使用DSAS可以降低Machines的平均退避時間、縮短平均封包延遲(Average Packet Delay, APD)並提高整體系統的吞吐量(Throughput)。

In this thesis, we propose a Dynamic Slot Allocation Scheme (DSAS) based on 802.11ah in Machine to Machine (M2M) environments. DSAS can effectively use the wireless resources to reduce the contention problems in M2M. In DSAS, we design two sets of high and low thresholds, respectively, to determine the levels (High, Average, Low) of machine sleeping time and the levels (High, Average, Low) of slot contention, respectively. The innovation of this thesis is that DSAS can allocate shorter sleeping-time machines to the slots that are more congestive. Similarly, the longer sleeping-time machines are allocated to the slots that are less congestive. In addition, to avoid unnecessary slot reallocations, the machines will use their original slots, when the contention level of slots is between high and low thresholds or the sleeping level of machines is between high and low thresholds. In order to analyze the performance of DSAS, we simulate it by modifying NS-3 Wi-Fi modules. In the simulation, we gradually increase the number of machines and randomly assigned the sleeping-time of machines. Simulation results, when compared to IEEE 802.11ah, show that using the proposed DSAS can reduce the average backoff time, shorten the average packet delay, and increase the overall system throughput.

致謝 i
摘要 ii
Abstract iii
目錄 iv
圖表目錄 vii
第一章 緒論 1
1.1 研究動機 1
1.2 研究方法 2
1.3 章節介紹 3
第二章 M2M網路 4
2.1 M2M的網路架構 4
2.2 802.11ah 8
2.2.1 802.11ah的Beacon 8
2.2.2 802.11ah的Restricted Access Window 9
2.3 文獻調查 10
2.3.1 叢集通訊(CC) 10
2.3.2 BS通訊 (BC) 13
2.3.3 Ad hoc通訊 (AC) 14
2.3.4 Wi-Fi通訊 (WC) 14
2.4 本論文機制 16
第三章 動態分配Machines的時槽 18
3.1 DSAS系統架構 18
3.2 DSAS運作方式 19
3.2.1 SL兩個臨界值的計算 21
3.2.2 CL兩個臨界值的計算 22
3.2.3 Slot的重新分配 23
3.2.4 新增與修改的欄位 26
3.3 DSAS運作流程 29
3.3.1 AP運作流程 30
3.3.2 Machine運作流程 32
第四章 結果與模擬討論 34
4.1 模擬程式架構和Pseudo Code 34
4.1.1 臨界值計算模組 35
4.1.1.1 ComputeSL_TH( ) 35
4.1.1.2 ComputeCL_TH( ) 38
4.1.1.3 CreatBitMap ( ) 39
4.1.2 隨機睡眠模組 41
4.1.3 Slot配置模組 41
4.1.4 RTS傳送模組 44
4.2 模擬結果與討論 45
4.2.1 模擬環境參數設定 45
4.2.2 Machines重新分配使用的Slot 46
4.2.3 Slot中ABT的比較 47
4.2.4 MAC Frame無法傳輸 48
4.2.4.1 在RCP中競爭失敗的Machines個數 48
4.2.4.2 無法排入DTP的Machines個數 49
4.2.5 Machines的平均封包延遲 50
4.2.6 整體系統的Throughput 52
第五章 結論與未來工作 54
5.1 結論 54
5.2 未來工作 55
References 56
Acronyms 60
Index 61

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