正交分頻多工系統在多重路徑下之同步問題

Abstract

正交分頻多工是一個可以提供高速傳輸的調變技術。目前在非對稱式數位用路迴路、數位音訊廣播、數位影像廣播及無線區域網路中已被廣泛地應用。 在此篇論文中，我們針對無線區域網路實體層中的封包偵測、頻率偏移估算以及碼框同步的問題提出模擬結果、分析以及新的方法。在封包偵測及頻率偏移中，除了提供模擬的結果外同時也作了效能推導以驗證模擬結果的正確性。在碼框同步中，除了兩種常用架構的實作、改良外，又提出了一個結合二種常用架構的優點，並將缺點摒除的新方法。在最後利用數學推導以及電腦模擬的方式，分析在不同通道下實體層同步的效能，不僅在理論推導和電腦模擬的結果上成功地得到驗證，而且在未來若有相同系統設計時也能夠進一步地對效能作出預測。

Orthogonal frequency division multiplexing (OFDM) systems have gained an increased interest during the past years, due to its effectiveness in mitigating the effects of multi-path spreading. It has been successfully applied in many applications, such as European digital broadcast radio system, digital television video (DTV), and wireless local area network (WLAN). In this thesis, the issue of packet detection, frequency offset estimation and frame synchronization for the physical layer of the IEEE OFDM WLAN system is investigated. New performance analysis is performed for packet detection and frequency offset estimation, respectively, and simulation results show that the analytic results agree very well with these of simulations for both AWGN and multi-path fading channels. In addition, new methods for frame synchronization are proposed that significantly outperform the traditional ones, especially in the multi-path fading environment.