載波頻率偏移一直是正交分頻多重接取上行系統中一個具有挑戰性的問題，其肇因為都普勒偏移亦或傳輸與接收之間震盪器不匹配，進而引發載波間干擾 (ICI) 與多重接取干擾 (MAI)，導致系統效能嚴重衰減。這篇論文中我們提出基於最小化重建誤差的聯合載波頻率偏移與通道估測演算法。首先介紹訊號模型及訂定領航訊號的配置。提出的演算法可以分成三項步驟。第一步驟使用線性最小化平方誤差進行通道估測。第二步驟形塑成本函數並使用二階法進行載波頻率偏移估測，爾後移除估測的載波頻率偏移。第三步驟以遞迴進行前兩個步驟的更新直到成本函數滿足停止準則為止。與其他演算法比較，此演算法不需進行奇異值分解，亦不需大量的訊號樣本。此論文最大的貢獻在於具有子載波分配自由度，可以被應用於任何基於正交分頻多重接取的系統。根據模擬結果，提出的方法具有貼近於完美通道估測的效能並能夠顯著的提升系統效能。

Carrier frequency offset (CFO) is a challenging problem in orthogonal frequency-division multiple access (OFDMA) uplink systems. CFO results from either a Doppler shift or transmitter-receiver local oscillator, causing intercarrier interference (ICI) and multiple access interference, which can lead to serious system performance degradation. In this scheme, we proposed a joint CFO and channel estimation method based on a minimum reconstruction error process. The signal model is introduced, and a pilot signal configuration is used as the setting. This proposed method can be divided into three steps. In the first step, the channel is estimated by the LMMSE method. The second step is the formation of the cost function, which uses a two step method for CFO estimation, and is followed by removing the estimated CFO from the system. In the third step, the recursion between the first and the second steps is performed until the stopping criterion is satisfied. Compared with other CFO estimation algorithms, our method does not need an eigen-based operation and numerous samples. The significant contribution of this scheme is the flexibility of the subcarrier assignment, which allows this scheme to be applied to any OFDMA-based system. Simulation results show that the proposed method achieved almost the same performance with perfect channel estimation and it significantly improved the system performance.

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