多載波分碼多工存取系統 (MC-CDMA) 是結合正交分頻多工 (OFDM) 與分碼多工存取 (CDMA)的技術，這樣的技術被視為第四代無線通訊系統重要的選擇之ㄧ，而此系統也存在著 CDMA 與 OFDM 的優缺點，缺點像是對載波頻率偏移非常地敏感還有多重存取干擾的問題等等，為了克服這些問題，對於接收機的設計必須同時地考慮進去。在本篇論文中，我們針對同步錯誤所產生的殘餘頻率偏移 (residual frequency offset，RFO) 提出了一個補償機制，而這裡同時使用王以及其他人所提出之改進過的部分平行干擾消除 (partial parallel interference cancelation) 偵測器來消除多重存取干擾 (multiple access interference，MAI)。除此之外，為了消除殘餘頻率偏移所產生之載波間的干擾 (intercarrier interference)，我們也使用一個Walsh-Hadamard 碼的子集合當作展頻碼而用它的特性來消除干擾。觀察 Hadamard 矩陣的公式，我們可以找出一半的展頻碼是反對稱的。基於這類展頻碼的選擇下，使得它擁有載波間干擾自身消除的特性，因此改進過的部份平行干擾消除偵測器可以降低載波間干擾的影響而且不會增加硬體實現的複雜度。在最後一階段的干擾消除中，RFO 的估計值將會在傳送端對原始的頻率偏移做補償，使相位旋轉的影響可以獨立於傳送資料的時間變數。由電腦模擬的結果可以看出本篇論文所提出的補償機制並使用 Walsh-Hadamard 展頻碼的子集合可以使用在改進過的部份平行干擾消除偵測器下有效地提高系統的效能。

In this thesis, we present a compensation scheme for residual frequency offset (RFO) caused by the synchronization errors, where the improved partial parallel interference cancellation (PPIC) detector proposed by Wang et al. is used to eliminate the multiple access interference (MAI) simultaneously. Besides, we also use a subset of the Walsh-Hadamard code as spreading codes to eliminate intercarrier interference (ICI) introduced by RFO. Based on the selection of the Walsh-Hadamard code, the improved PPIC can reduce ICI without increasing implementation complexity. Computer simulation results show that the proposed compensation scheme with a subset of the Walsh-Hadamard code for the improved PPIC detector can effectively enhance the system performance.

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