Applying extended kalman filters to carrier frequency offset estimation in OFDM systems / Yi-Fan Huang.

[[abstract]]在正交多載波通訊系統中，若傳送端與接收端的本地震盪器載波頻率沒有同步,會產生載波間交互干擾（ICI）且系統效能會降低。因此正交多載波通訊系統如何消除或減少頻率偏移的影嚮是非常重要的。 幾個被用來解決OFDM系統的頻率同步問題或減少ICI的方法呈現在此論文中。一個簡單的方法是在頻域中執行重複編碼，來減少ICI，稱為載波間交互干擾自我消除機制。但是由頻率偏移所引起的相位旋轉並無法單獨用此機制解決。另一方法是用統計特性來估測頻率偏移，稱為最大相似度估測（MLE）。MLE即使在SNR小的環境下，依然可得到正確的估測結果。但是MLE的估測範圍不能超過載波區間的50%。所以在此論文中也介紹了利用延展式卡曼濾波器的方法來估測系統頻率偏移的問題。延展式卡曼濾波器可以有效率及精確的估測出頻率偏移，同時也不受限於MLE的估測範圍不能超過載波區間的50%。最後，這些方法的模擬結果與結論也被呈現在此論文中。[[abstract]]In orthogonal multicarrier communication system, if carrier frequency between the local oscillators at the transmitter and at the receiver unsynchronize, the intercarrier interference (ICI) will produce and system performance will be degraded. Thus it is very important to eliminate or reduce the effect of frequency offsets in the OFDM systems. Several methods use to solve frequency synchronization problem or alleviate ICI in orthogonal frequency division multiplexing (OFDM) system are presented in this thesis. A simple method performs repeated coding in frequency domain to alleviate ICI significantly, called ICI self-cancellation scheme. However, the phase rotation caused by frequency offset cannot be solved by this method alone. Another method uses statistical property to estimate frequency offset, called maximum likelihood estimation (MLE). The MLE could get accurate estimated result even in the small SNR environment. However, the estimate range of MLE cannot be larger than 50% of subcarrier spacing, this is a restriction of MLE. In this thesis, we also introduce the extended Kalman filter scheme to eliminate or reduce the effect of frequency offset in the OFDM systems. The extended Kalman filter scheme can efficiently and accurately estimate the values of frequency offset and no such limitation that the estimate range of MLE cannot be larger than 50% of subcarrier spacing, Finally, the simulation results of these methods are presented, and the conclusions are also given in this thesis