多輸入多輸出正交分頻多工(MIMO-OFDM)系統是一種結合MIMO信號處理和OFDM的新傳輸架構，在本篇論文中，我們針對MIMO-OFDM提出一個全新且完整的同步機制，包含了粗調時間擷取(coarse time acquisition)，載波頻率偏移粗略估計(coarse carrier frequency offset estimation)，細調時間擷取(fine time acquisition)，載波頻率偏移細部估計(fine carrier frequency offset estimation)。在提出的同步機制中，粗調時間擷取和載波頻率偏移粗略估計是採用舊有的OFDM同步技術，目的是要先取得同步上初步的估計子，因為接下來的細調時間擷取和載波頻率偏移細部估計需要有初步的同步資訊來協助運作。我們所提出的細調時間擷取是根據MIMO-OFDM的離散傅立葉通道估測法(DFT-based channel estimation)所估計出的通道增益的資訊來做細部時間的擷取，此方法可以提供從任一傳送端所傳送到任一接收端支線的信號一個準確且專屬的信號起始點。利用細調時間擷取所得到的資訊，我們可以對載波頻率偏移估計決定一個適當的相關性運算的範圍來得到較好的估計效能。由電腦模擬結果可看出本篇論文所提出的細調時間擷取方法和傳統的同步方法比較下，會有明顯效能增益，且效能不會隨著天線數增加而有所影響。除此之外，摩結果也可看出本篇論文所提出的載波頻率偏移細部估計的確可以利用細調時間擷取所得到的資訊來決定出適當相關性運算的起始點和運算的範圍來提供效能更好的載波頻率偏移估計器。

Multiple-input multiple-output orthogonal frequency division multiplexing (MIMO-OFDM) is a new transmission scheme that combines MIMO signal processing and OFDM techniques. In this thesis, we propose a new training sequence structure along with a complete synchronization scheme for MIMO-OFDM systems. The proposed synchronization scheme includes coarse time acquisition, coarse carrier frequency offset estimation, fine time acquisition, and fine carrier frequency offset estimation. In the proposed synchronization scheme, we adopt existing techniques to obtain initial timing and frequency offset estimates for the proposed fine time acquisition and fine frequency offset estimation methods. The proposed fine time acquisition method is assisted by the estimated channel gain, which is obtained by a recently proposed DFT-based channel estimator. The proposed approach is able to provide each transmit-receive branch with an accurate and dedicated timing instant. Based on the timing instants obtained, the proposed fine carrier frequency offset estimator decides a proper correlation range to obtain a better estimate. Computer simulation results show that, the proposed fine time acquisition method can provide significant performance gain over a conventional method. Unlike the conventional method, the proposed approach provides accurate and comparable estimates regardless of the number of transmit antennas. In addition, the proposed fine carrier frequency offset estimator can improve the coarse frequency offset estimator by finding a proper correlation range and averaging estimates obtained from different transmit-receive branches.

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