移動WiMAX系統之導引碼輔助疊代式通道估測

Abstract

正交分頻多工系統為新一代無線通訊系統最常使用的技術，如IEEE 802.11 a/g/n， IEEE 802.16， IEEE 802.20，數位電視，數位廣播等許多系統均採用此技術。移動傳輸是未來無線通訊系統的趨勢之一，如IEEE 802.16-2005 可支援到車速120 km/hr，而IEEE 802.20 更可以支援到車速 250 km/hr。許多通道估測法，使用大量的導引符號，以及緩衝暫存器來估測通道。在本論文中，我們使用兩種通道估測，decision directed 和expectation maximization。此通道估測可追蹤時變通道,以及使用少量導引符號。最後，藉由電腦模擬驗證此一新演算法在移動的環境中並使用IEEE 802.16-2005 的規格下，可有效的改善錯誤率。

Orthogonal Frequency Division Multiplexing (OFDM) is a popular technique in modern wireless communications. There are many systems adopting the OFDM technique, such as IEEE 802.11 a/g/n, IEEE 802.16, IEEE 802.20, and Digital Video Broadcasting, etc. On the other hand, mobility is an important issue that needs to be taken into account in the design of future wireless communication systems. For example, IEEE 802.16-2005 supports vehicle speed up to 120 km/hr, and IEEE 802.20 supports vehicle speed up to 250 km/hr, causing the channel seen by the receiver time-varying. Some channel estimators use a large number of pilot symbols to estimate the channel parameters, or use buffer to obtain desired channel parameters. In this thesis, we show two channel estimation approaches, namely the decision directed based and expectation maximization based approaches that can track the time-varying channel vectors with less insertion of pilot symbols. Finally, we evaluate the performance of the proposed systems under mobility using IEEE 802.16-2005 standard and confirm that it achieves good SER performance.