近年來多重存取正交分頻多工系統被視為未來多用戶無線通訊的主要技術。系統中受載波頻率偏移的影響，會破壞子載波正交性並產生子載波間干擾及多重使用者間干擾。過去研究中，我們已提出載波頻率偏移於接收端更正的新方法，能有效降低子載波間或多重存取干擾影響，讓整體或特定使用者效能達到最小均方差並降低錯誤率。在此系統架構中，估測共同載波頻率偏移是運用決策回饋的方式適應性收斂至最小均方差。本論文研究共同載波頻率偏移之最小均方差解，並利用其結果分析驗證使用適應性決策回饋的方式獲得之共同載波頻率偏移的可靠性。模擬結果顯示適應性決策回饋的方式可獲得最佳共同載波頻率偏移之更正並有效達到最小均方差效能。

Recently, multi-access orthogonal frequency division multiplexing (OFDMA) has drawn a lot of attention in next-generation multiple access wireless communication technologies. The carrier frequency offsets in OFDMA systems can destroy the orthogonality among subcarriers and produce the intercarrier interference (ICI) and multiuser interference (MUI). In our previous works, we proposed a common carrier frequency offset (CCFO) correction scheme at the OFDMA receiver, which can reduce the ICI/MUI effect and the bit error rate by minimizing the mean square error (MSE) for demodulated data subject to the overall users or some specific users. In the scheme, the CCFO is obtained by adaptively converging the MSE between the demodulated output and the decision feedback data. This paper studies the minimum MSE solution for the CCFO value, and the result is exploited to verify the adaptive CCFO estimation algorithm by means of the decision feedback. Simulation results show that the adaptive decision feedback scheme for CCFO estimation is effective and the minimum MSE performance is well achieved.

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