本篇提出利用獨特字之多用戶載波頻率偏移估測基於離散傅立葉擴展正交分頻多工之上行鏈路架構的方法。
載波頻率偏移可能來自於接收端與傳送端的震盪器之不匹配的情形，也可能是由使用者與基地台存在的相對速度所導致的。載波頻率偏移的存在會造成時域信號之相位產生線性的遞加或遞減，然而此變異的相位會是整個系統表現下降的主要原因。
一般來說，離散傅立葉擴展正交分頻多工波形多用於上行鏈路系統。在接收端，基地台必須面對來自多用戶之多載波頻率偏移的問題，然而這是在下行鏈路比較不會面臨的問題。現今有很多文獻基於正交分頻多工的架構下對載波頻率偏移估測設計。在現有的方法當中，和以正交分頻多工為基礎設計的載波頻率偏移之估測方法相比，以離散傅立葉擴展正交分頻多工為基礎而設計的載波頻率偏移之估測方法之現有文獻是相對不足的，特別是如同此篇論文提出在時域進行估測的方法。
此篇提出的方法可以在多用戶同時在使用通道傳輸的情境下，進行載波頻率偏移的估測，是利用獨特字在傳送端以及接收端的關係而設計的方法。該系統可以適用於任何的載波排列情境。該系統在通道被占滿時，載波頻率的估測值也可以達到足夠的準確度。此篇提出的方法是在時域所設計，與現有利用犧牲頻寬的估測方法相比，可以大幅度的增加頻寬的使用效益。

A multi-user carrier frequency offsets (CFO) estimation method with the utilization of unique word sequences bases on the discrete Fourier transform spread orthogonal frequency division multiplexing (DFT-s-OFDM) waveform uplink system is proposed in this thesis.

The CFO comes from the mismatch of oscillators or the velocity between users and base stations. The shift of the signal in frequency domain will cause a linearly increasing or decreasing phase on the signal in time domain. The phase difference is one of the main reasons why the performance of the system degrades.

In general, the DFT-s-OFDM waveform is used in the uplink system. At the receiver, the base station needs to confront multiple CFOs from different users which is the problem that a downlink system doesn’t have. There is great many literature discuss the CFO estimation issue in orthogonal frequency division multiple access (OFDMA) system. Existing methods discuss about multiple CFOs problem in a DFT-s-OFDM uplink system is insufficient compare to designs for OFDMA system. Especially for an estimation method that is designed in the time domain as the proposed method in this thesis.

The method is capable to estimate multiple CFOs under the scenario that the channel is used for transmission by different users simultaneously. It utilized the relation between the unique word sequences at the transmitter and the receiver. The method can adapt to any carrier assignment schemes (CAS). The method can reach a sufficient CFO estimation accuracy in the full-loaded scenario. The estimation algorithm is designed in the time-domain. Compare to those existing methods which estimate the CFO by sacrificing the transmission bandwidth, our method achieves higher bandwidth efficiency.

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