載波頻率偏移估測法於正交分頻多工系統之效能改進

Performance Improvement of Carrier Frequency Offset Estimation Methods in OFDM System

楊東海(Dong Hai Yung)

指導教授 ： 呂振森

國立臺北科技大學/電資學院/電機工程系研究所/碩士(2009年)

https://doi.org/10.6841/NTUT.2009.00512

摘要

隨著使用者需求日益漸增，對頻寬的要求越來越重要，OFDM是一種具有高頻譜效率的調變技術，可以在有限頻寬下進行高資料量傳送。然而OFDM對頻率同步之錯誤非常敏感，只要有些許載波頻率偏差，就會造成載波間干擾，使系統效能大幅降低。故本論文針對接收端本地振盪器非理想狀況所造成的頻率偏移進行研究，以載波頻率偏移估測演算法為研究基礎進行改良，提出結合偏移量補償法的載波頻率偏移估測新方法。此一方法主要是套用在近年來提出的使用領導符碼搭配MLE結合ICI自我消除演算法上，可在相同頻寬效益及不增加過多計算複雜度的情況下來改善系統效能。經由電腦模擬證明，此一方法不僅能增加獲取載波頻率偏移量的範圍，亦對系統效能有明顯的改善。

關鍵字

正交分頻多工 ； 載波頻率偏移 ； 最大概似估測法 ； 載波間干擾 ； 領導符碼

並列摘要

With increasing demands from users, the issue of bandwidth efficiency becomes more and more important. The OFDM is a modulated technology with high bandwidth efficiency. It can provide high data rates with limited bandwidth. However, one of the drawbacks is their extreme sensitivity to frequency synchronization errors. With slight carrier frequency offset (CFO), it will result in the inter-carrier interference (ICI) which causes severe degradation on the system performances. Therefore, this thesis is mainly to research into the carrier frequency offset estimation methods for the CFO induced by imperfections of local oscillator’s frequency at receiver. A new carrier frequency offset estimation method combined with offset compensation was proposed. This method is based on the recent pilot-based carrier frequency offset estimation method which integrates with maximum likelihood estimation and ICI Self-cancellation algorithm. The proposed method can improve the system’s performance without increasing a lot of complexity under the same bandwidth efficiency. According to the computer simulation, our results show that it can not only extend the estimation rage of carrier frequency offset, but also increase the system performance.

並列關鍵字

OFDM ； Carrier frequency offset ； Maximum Likelihood Estimation ； Inter-Carrier interference ； Pilot Symbol

參考文獻

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