無線寬頻存取很重要的一個步驟，是下行鏈路(Downlink)剛建立時接收端所必須做的訊號偵測、時間與載波頻率的同步以及搜尋目前所屬的細胞基地台，這個動作就是所謂的初始的細胞搜尋(initial cell search)。一般要完成以上動作，基地台會傳送額外的引導符元用來做基地台的辨認，而在3GPP LTE系統利用的即是兩個同步訊號，包含主要同步訊號(Primary Synchronization Signal, PSS)與次要同步訊號(Secondary Synchronization Signal, SSS)。在LTE下行傳輸鏈路使用的是OFDM的技術。然而，OFDM有對同步誤差敏感的缺點，例如載波頻率偏移(CFO)會破壞子載波間的正交性，產生子載波間干擾，使系统性能惡化。

本論文首先詳細說明同步及細胞搜尋的各項流程。針對PSS的處理提出了創新的演算法，包含了理論分析以及推導，並且將模擬結果與現有文獻相比，提出的方法除了能有效減少細胞搜尋的錯誤率。最重要的是，本論文提出的方法能更準確的估測整數倍載波頻率偏移(ICFO)並且修正之，進而改善整體效能。此外，我們的演算法運算複雜度亦較低。

In cellular communication systems the mobile station (MS) must perform initial synchronization and search for a base station to set up the downlink access. This process is the so-called initial cell search. To accomplish the operations mentioned above, two synchronization signals, the primary synchronization signal (PSS) and the secondary synchronization signal (SSS), are periodically transmitted from base station in the 3GPP LTE (Long Term Evolution) system. It is announced OFDM signal is applied to downlink transmission in the LTE cellular network. However, OFDM signal is sensitive to synchronization error, such as carrier frequency offset (CFO). CFO, which exists between the transmitter and the receiver, causes loss of orthogonality among subcarriers and inter-carrier interference (ICI) and degrade the system performance.

In this thesis all the procedures of synchronization and initial cell search are specified. Two Innovative processing algorithms for PSS, including the theoretical analysis and deduction, are provided. Most important, the proposed schemes are able to evaluate the ICFO more accurately and improve the error rate effectively. Comparisons between the proposed schemes and the existing ones are illustrated in the simulation results. Furthermore, the proposed schemes also reduce the computational complexity.

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