廖婉君臺灣大學：電機工程學研究所江致和Chiang, Chih-HeChih-HeChiang2007-11-262018-07-062007-11-262018-07-062006http://ntur.lib.ntu.edu.tw//handle/246246/53549IEEE 802.16 WiMAX網路是目前相當受到矚目與擁有發展潛力的一種都會型無線寬頻網路接取技術。不像其他集中排序 (centralized-scheduling) 網路，IEEE 802.16在分時多工 (TDD) 的模式下，上下行的頻寬可以做動態的調整，然而在IEEE 802.16 WiMAX網路下，上下行的頻寬比例並沒有明確規定。於是，我們推導出適合IEEE 802.16 WiMAX網路的asymmetry ratio，確定只要asymmetry ratio小於1，TCP就能夠在IEEE 802.16 WiMAX網路中正常的運作。接著，只要利用基地台所觀察到的網路使用情況和我們所定義的asymmetry ratio，我們就可以找出最好的上下行頻寬比例。我們分析此提出的機制並用ns-2模擬其效能，其結果顯示我們的動態調整上下行頻寬比例的機制，比起其他任一固定上下行頻寬比例的方式，效能有明顯的提升。IEEE 802.16 WiMAX network is viewed as a promising broadband wireless metropolitan area network technology. Unlike ordinary centralized-scheduling networks, the ratio of downlink bandwidth to uplink bandwidth in WiMAX network can be adjusted adaptively with TDD duplexing technique. However, there’s no specification defining how to adjust the DL/UL bandwidth ratio. Thus, we define the asymmetry ratio appropriate for IEEE 802.16 network. As the ratio is less than one, TCP behaves normally. Then, by using the network situation observed through base station and the asymmetry ratio we defined, we can find the best DL/UL bandwidth ratio. We analyze the proposed mechanism and conduct simulation using ns-2. The results show that our dynamic DL/UL bandwidth ratio mechanism has better performance compared to any fixed DL/UL bandwidth ratio.Chapter 1 Introduction 1 1.1 IEEE 802.16 WiMAX Network 2 1.2 The Effects of Bandwidth Asymmetry on TCP Performance 6 1.3 Related Work 8 1.3.1 The Effects of Asymmetry on TCP Performance 8 1.3.2 IEEE 802.16 8 1.4 Motivation 9 1.5 Thesis Organization 10 Chapter 2 Analysis of the Effects of Bandwidth Asymmetry on TCP Performance in IEEE 802.16 WiMAX Networks 11 2.1 System Model 11 2.2 Notation and Assumption 12 2.3 One-way TCP Transfer 14 2.3.1 The Effects of IEEE 802.16 MAC Layer on Bandwidth Asymmetry 14 2.3.2 The Effects of Bandwidth Asymmetry on Round Trip Delay 17 2.4 Two-way TCP Transfer 19 2.4.1 The Effects of IEEE 802.16 MAC Layer on Bandwidth Asymmetry 19 2.4.2 The Effects of Bandwidth Asymmetry on Round Trip Delay 22 Chapter 3 Dynamic DL/UL Bandwidth Ratio Adjustment Mechanism 24 3.1 Two-way TCP Transfer 24 3.2 Flow-Chart of Dynamic DL/UL Bandwidth Ratio Adjustment 28 Chapter 4 Simulation Results 30 4.1 Simulation Environment 30 4.2 Performance Metrices 31 4.3 Simulation Results 31 4.3.1 One-way Simultaneous TCP Transfers 32 A . Aggregate Throughput 32 B . Upstream User Service Time & Access Delay 35 4.3.2 Two-way Simultaneous TCP Transfers 37 4.3.2.1 Scenario One 37 4.3.2.2 Scenario Two 41 Chapter 5 Conclusions and Future Work 44 5.1 Conclusions 44 5.2 Future Work 45 References 46555673 bytesapplication/pdfen-US802.16都會型無線寬頻網路非對稱比例IEEE 802.16WiMAXasymmetry ratiothesishttp://ntur.lib.ntu.edu.tw/bitstream/246246/53549/1/ntu-95-R93921031-1.pdf