由於循環延遲分集機制在傳送端只需要一個反離散傅立葉轉換運算，因此在多輸入多輸出正交分頻多工系統中，循環延遲分集提供了一個低複雜度且可提高傳送分集的方法。但傳統應用於多輸入多輸出正交分頻多工系統中的最佳化導航符元設計，無法直接用在具有循環延遲分集機制的正交分頻多工系統中，因此本論文首先討論如何推導出可讓最小平方誤差與最小均方誤差的通道估測方法得到最小均方誤差的準則。然後此準則可被利用來發展出最佳化導航符元序列的設計方法。特別的是，我們所提出的方法只需要一個正交分頻多工系統符元就得到目前的通道資訊。最後從模擬結果可確定，我們所提出的導航符元設計可讓最小平方誤差與最小均方誤差的通道估測方法得到最小的均方誤差。

Since only one inverse discrete Fourier transform (IDFT) operation is required for cyclic-delay diversity (CDD) schemes at the transmitter, a low-complexity approach of increasing the transmit diversity can be provided in multiple-input multiple-output (MIMO) orthogonal frequency division multiplexing (OFDM) systems. However, the optimal pilot sequences, which minimize the mean square error (MSE) of the channel estimate in traditional MIMO-OFDM systems, can not be applied to CDD-OFDM systems directly. Therefore, this paper first derives the criteria which yield the minimum MSE of both the east square (LS) and the minimum mean square error (MMSE)channel estimates in CDD-OFDM systems. Then the derived criteria are used to develop a general methodology for determining the optimal pilot sequences. Particularly, the proposed approach requires just one OFDM symbol to estimate the channel status. From the simulation results, we confirm that the proposed pilot design minimizes the MSE of both the LS and the MMSE channel estimates.