針對下一世代無線網路所設計之訊框聚合鏈路適應演算法

Abstract

鏈路適應在無線網路中是一個非常重要的議題。利用鏈路適應的演算法，無線通訊系統動態地針對不同的通道條件設定調變模式、傳輸速率或任何可調的系統參數，藉此得到較未使用任何鏈路適應演算法之系統更佳的效能。本論文目的在IEEE 802.11n 標準下制定一個表現佳的鏈路適應演算法。在第一章中，不同的無線網路、IEEE 802.11 無線區網的演進、各類已存在的鏈路適應演算法以及本論文提出的訊框聚合鏈路適應(FALA, Frame-Aggregated Link Adaptation)演算 法之概念將被介紹。在第二章節中，對IEEE 802.11n 標準在媒體存取控制(MAC,Medium Access Control)層、實體(PHY, Physical)層的特性及兩個鏈路適應演算法有詳細地説明。MAC/PHY 層的位元錯誤率(BER)、系統飽和吞吐量分析以及FALA算法則在第三章節中詳細地被解說。在效能評比的部份，本論文所提之FALA 演算法、跨層鏈路適應(CLA, Cross-layer Link Adaptation)演算法以及自動速率調降(ARF, Auto Rate Fallback)演算法將被比較。最後，結論為本論文所提之FALA 演算法較已存在的CLA 及ARF 演算法有較佳的表現。

Link adaptation is an important issue in wireless networks about applying some mechanisms to set different modulation modes or data rates corresponding to different channel conditions dynamically in purpose of performance better than the one without any link adaptation algorithm utilized. In the first chapter, some different wireless networks, evolutions of IEEE 802.11 WLANs, concepts of link adaptation and ideas of the existing/proposed frame-aggregated link adaptation (FALA) algorithm are introduced. In the second chapter, features of IEEE 802.11n medium access control (MAC) and physical (PHY) layer, and two existed link adaptation algorithm will be briefly introduced. In the third chapter, evaluation of bit error rate (BER) in PHY/MAC layer, analysis of saturated goodput, and mechanism of FALA algorithm are illustrated in detail. In performance evaluation, the numerical result is verified with the simulation result, and compared to the existed automatic rate fallback (ARF) and cross-layer link adaptation (CLA) algorithms. Finally, a better performance with FALA algorithm utilized will be shown, and the conclusion will be drew that the proposed FALA algorithm works well in link adaptation and outperforms the existed two algorithms.