多輸入多輸出正交分頻多工系統之決策回授以消除符元間干擾及通道追蹤

Abstract

在正交分頻多工系統中，當脈衝響應長度大於前置循環訊號的長度時，符元間的干擾就會產生而將嚴重地降低系統效能。在本論文中，我們結合了決策回授及環形重建的方法以處理這些問題。我們所提出的演算法中，採取遞迴的方法以消除符元間干擾並對符元做環形重建。在處理的時變的無線通道上，我們也提出了在時域上追蹤通道變化的有效方法，能藉著傅立葉轉換而降低系統的運算複雜度。之後更進一步將此方法延伸到多輸入多輸出正交分頻多工系統中。模擬的結果顯示，當符元間干擾出現時，我們的所提出的演算法，能有效地加強正交分頻多工系統的效能。

In OFDM systems, when the channel response is longer than cyclic prefix (CP), intersymbol interference (ISI) will occur. The ISI can seriously degrade the performance of OFDM systems. In this thesis, we combine the decision feedback and cyclic reconstruction techniques to remedy this problem. The proposed method cancels ISI and reconstructs the circular structure of the OFDM symbol iteratively. To cope with time-variant wireless channels, we also propose an efficient time-domain channel-tracking scheme. The proposed scheme allows the use of FFT such that its computational complexity is low. Finally, we extend the proposed methods to multi-input multi-output (MIMO) OFDM systems. Simulations show that the proposed methods can greatly enhance the performance of OFDM systems in the presence of ISI.