應用於無線多輸入多輸出基頻處理器載波同步之研究

Abstract

多輸入多輸出正交多頻分工系統是下一代無線通訊系統一個很重要的技術。然而這個技術的實現伴隨著載波同步的問題發生，其中有兩個影響系統效能的重要因素，它們分別是IQ不平衡效應及載波頻率偏移。IQ不平衡效應主要是由I通道和Q通道的信號誤差所導致而載波頻率偏移則是由傳送端和接收端的射頻電路頻率不同步所引起。這兩個問題都會危害到系統中子載波的正交性，尤其是在系統採用高信號調變模式的時候。在本篇論文中將會提出適應性IQ偵測和相位恢復的演算法來改善多輸入多輸出正交分頻多工系統的效能。從模擬的結果可知在受到時變變異量百分之三十的IQ不平衡效應， 適應性IQ偵測可達到5dB的改善，而在頻率偏移的部份，相位恢復的演算法能夠有效的修正頻率偏移偵測的誤差。最後相位恢復的演算法是以TSMC 0.13 µm的製程實做出來，邏輯閘的數目約為240K。

Multiple-Input Multiple-Output Orthogonal Frequency Division Modulation (MIMO-OFDM) is the candidate for next generation of wireless communication. However, implementation of MIMO-OFDM suffers from the problem caused by carrier synchronization. This thesis will address two performance degrading effects of carrier synchronization, namely, I/Q imbalance and Carrier Frequency Offset (CFO). The I/Q imbalance is caused by the mismatch between the I and Q branches and the CFO is caused by the mismatch of radio frequency circuits between the transmitter and receiver. Both of them will damage the orthogonality between the subcarriers, mostly when high order modulation schemes are applied. In this thesis, an adaptive I/Q estimation scheme and phase recovery has been proposed to improve the performance of MIMO-OFDM system. From simulation results, it is shown that the improvement of adaptive I/Q estimation is about 5 dB under the time-varying I/Q imbalance with variation 30% and the phase recovery can effectively correct the CFO estimation errors. Finally, the phase recovery is implemented by TSMC 0.13 µm CMOS process and the gate count is about 240 K.