在此篇論文中，利用不完全的Zadoff-Chu訓練序列，我們於正交分頻多工(OFDM)雙向放大轉送中繼系統中，提出一種聯合時間同步與載波頻率偏移(CFO)的估測技術。在訓練序列的設計中，兩個終端點的訓練序列在頻域與時域均有效被區隔，以達到抑制訓練序列間的互相干擾。此類的訓練序列結構能聯合估測時間延遲及載波頻率偏移，而盡我們了解所能，在OFDM雙向放大轉送中繼系統中，尚未有針對此問題所提出相關之聯合設計。我們所提出之聯合估測方法可重複執行，以改善整體同步效能，而通常經過兩次迭代就足以提供符合要求的效能表現。為了降低運算複雜度及抑制高功率峰均比(PAPR)的問題，我們亦對會影響時域訓練訊號的主波瓣寬度之參數，提供一些適當選擇此參數的分析結果。經由模擬結果顯示，在OFDM雙向放大轉送中繼系統中，我們提出的聯合估測方法，相對於其他時間同步方法結合傳統CFO估測，有較好的時間同步效能表現，且又可達到相近的CFO估測效能表現。

In this thesis, we propose a joint time synchronization and carrier frequency offset (CFO) estimation scheme using partial Zadoff-Chu sequences for orthogonal frequency-division multiplexing (OFDM)-based two-way amplify-and-forward (AF) relay systems. In the preamble design, the training signals for the two terminals are not only separated in the frequency domain but also isolated in the time domain so as to limit their mutual interference in both domains. Such a preamble structure allows joint estimation of timing delays and CFOs and, to the best of our knowledge, there is no related joint design in OFDM-based two-way AF relay systems. This joint estimation process could be repeated to improve the overall synchronization performance, where two iterations are often enough to provide satisfactory performance. To reduce the computational complexity and to alleviate the peak-to-average power ratio problem, we also provide some analysis results for appropriately determining the parameter that affects the width of the main lobe of the time-domain training signal. Simulation results demonstrate that the proposed joint scheme has superior timing performance to a previous time synchronization scheme combined with the conventional CFO estimation method for OFDM-based two-way AF relay systems, where both achieve similar CFO estimation performance.

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