用於雙振幅調變信號下結合載波恢復器之二階段等化器

Abstract

在通訊系統中因通道衰減會造成符號間干擾。本論文中採用絕對值演算法(CMA)的盲蔽等化器(Blind equalizer)將通道所造成的符號間干擾消除，再由載波相位恢復器對相位錯誤作補償。但因經過CMA盲蔽等化器所得之輸出信號星狀圖(Constellation)的收斂效果不佳，故在此加入第二級的最小均方誤差(LMS)決策反饋(Decision Feedback)等化器，以求得較佳之信號星狀圖(Constellation)的收斂。在作第二級決策反饋等化器的同時，也可將載波恢復器(Carrier Recovery)合併使用，使其作信號星狀圖收斂的同時也作反相位旋轉。此處的第二級決策反饋等化器，採用順向濾波器(FFF)與反饋濾波器(FBF)組合成三種不同的型式。最後由輸出信號星狀圖的均方誤差(MSE)值可看出，只採用順向濾波器的第二級決策反饋等化器的輸出效果最佳。

In the communication systems, the channel fading will cause Inter-symbol interference (ISI). In this thesis, the constant modulus algorithm (CMA) equalizer is used to eliminate ISI. Carrier recovery loop is used to compensate the phase error. However, the convergence of the output constellation from CMA equalizer is not satisfactory. Therefore, we use the Least Mean Square-decision feedback equalizer (LMS-DFE) as the second-stage equalizer to overcome the constellation convergence problem. The second-stage equalizer can be combined with carrier recovery unit. It can be any combination of Feed-Forward Filter (FFF) and Feed-Back Filter (FBF). From the Mean Square Error (MSE) results we can see that the equalizer that just uses FFF achieves the best performance.