隨著Wi-Fi的配置越來越多也越來越密集，傳統的802.11MAC層DCF接入方式的問題也越來越凸顯出來。為了提供密集場景高效率的無線區域網路（HEW）技術，IEEE 802.11成立了IEEE 802.11ax工作小組，針對密集分布場景的問題進行大幅度的修改。IEEE 802.11ax引入OFDMA，實現多用戶傳輸(MU)，並且提出基於OFDMA的隨機存取協定。在本論文中，我們提供了一種簡單且準確的分析模型，用於在飽和條件下研究UL OFDMA RA的系統效率和延遲性能，並且進行模擬以驗證分析結果。此外，我們使用此分析模型來確定最大化系統效率並且歸類出系統參數對系統效率的最佳化規則。

Recently, a revolutionary effort to seek fundamental improvement of 802.11, known as IEEE 802.11ax, has been approved to deliver high efficiency wireless local area network (HEW) technologies for dense scenario. The de-facto random access mechanism of IEEE 802.11ax is uplink OFDMA-based random access (UL OFDMA RA) mechanism. In this thesis, we provide a simple but accurate analytical model to study the system efficiency and delay performance of UL OFDMA RA under saturated condition, in the assumption of a finite number of stations and ideal channel conditions in a single-hop WLAN. Simulations are conducted to validate analytical results. In addition, we use this analytical model to identify an appropriate OFDMA-based random access parameter set (RAPS) that maximizes the system efficiency, a feature which is essential for system design and configuration.

中文摘要 I
Abstract II
Chapter 1 Introduction 1
Chapter 2 Instability of DCF 3
Chapter 3 Related Works 5
Chapter 4 Preliminary 7
4.1 MU-MIMO 7
4.2 UL OFDMA Random Access 10
Chapter 5 Analytical Model 12
5.1 Packet Transmission Probability 12
5.2 Random Access Efficiency 17
5.3 Model Validation 18
Chapter 6 Performance Evaluation 20
6.1 Maximum System Efficiency and Minimum Access Delay 20
6.2 Effects of System Parameter 21
Chapter 7 Conclusion 28
Reference 29

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