應用於正交分頻多工無線區域網路系統之連續式時間同步法

Abstract

正交分頻多工系統，如IEEE 802.11a，廣泛應用於無線區域網路。而正交分頻多工系統中的時間同步是相當重要的議題，嚴重的時間誤差將造成後續解碼失敗。所以對封包傳輸式的正交分頻多工系統很需要一個快速且精準的時間同步器，同步器還要能處理一些干擾因素，如雜訊、多重路徑效應和頻偏效應，同時能達到理想的效能。 論文中將提出一個應用於正交分頻多工無線區域網路之連續式時間同步法，其中包含封包偵測，頻偏估測及傳送符元時間同步，最後會提出完整的連續式時間同步架構。除了連續式時間同步法之外，同時還會比較目前一些基本的時間同步器。模擬結果顯示，連續式時間同步法誤差較小且能快速收斂，尤其更能適應於嚴重的衰減通道下的環境。

The OFDM system such as IEEE 802.11a is utilized widely in the Wireless LAN. The timing synchronization is an important topic for the OFDM system since the serious timing error will destroy the proceeding demodulation. A rapid and accurate timing synchronizer is needed for the packet-based OFDM system. Also it needs to deal properly with some interference factor such as noise, multipath effect, and frequency offset etc; concurrently, achieve a desirable performance. In this thesis, a successive timing synchronization fit for OFDM-based Wireless LAN is proposed. The proposed timing synchronization includes packet detection, frequency offset estimation, and symbol timing synchronization and an accomplished architecture of the successive timing synchronization is proposed as well. Besides, some fundamental timing synchronizers are discussed. The proposed successive timing synchronization is comparatively more powerful than some fundamental timing synchronizations as a consequence of the speedy convergence and low timing error. Especially, it is robust enough in the serious fading channel as confirmed by the simulation results.