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研究生:沈柏中
研究生(外文):Po-Chung Shen
論文名稱:正交分頻多工系統中使用頻率偏移校正方法之載波間干擾消除技術
論文名稱(外文):An Intercarrier Interference Cancellation Technique Using Frequency Offset Correction for OFDM Systems
指導教授:王晉良
指導教授(外文):Chin-Liang Wang
學位類別:碩士
校院名稱:國立清華大學
系所名稱:通訊工程研究所
學門:工程學門
學類:電資工程學類
論文種類:學術論文
論文出版年:2003
畢業學年度:91
語文別:英文
論文頁數:41
中文關鍵詞:正交分頻多工載波間干擾頻率偏移
外文關鍵詞:OFDMinter-carrier interferencefrequency offsetdoppler
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當正交分頻多工 (OFDM) 技術應用在移動系統時,載波間干擾 (ICI)成為一個額外影響系統效能的重要因素;這是由於載波頻率間隔 (subcarrier spacing) 縮短以及都卜勒效應 (Doppler effect) 浮現,使得載波間的正交特性 (orthogonality) 易受破壞的緣故。都卜勒效應造成的影響其實和單一系統頻率偏移 (frequency offset) 的情況相似,但是在多重路徑 (multipath) 的環境下,它更包含了伴隨著來自不同路徑的信號而產生的相異頻率偏移量。由於傳統上處理單一系統頻率偏移所用的頻率同步技術無法估測此多樣頻率偏移量,而頻域等化器 (FEQ) 因缺乏準確的快速通道估測技術配合,亦難以有效地消除此類之載波間干擾,因此我們亟需更具可行性的方案。
在此篇研究中,我們採取一種校正載波頻率偏移的方式來達到載波間干擾消除的效果。在通道模型為非全向性散射 (non-isotropic) 的假設下,我們首先提出一新型的頻率偏移估測器,用以估測都卜勒效應造成的多項頻率偏移量;其後,藉由理論分析,我們推導出載波間干擾能量的數學模型,並利用此模型找出由各路徑之頻率偏移量計算最佳頻率校正值的方法。從所求得之最佳頻率校正值的表示法中,我們瞭解此頻率偏移校正器的確具有載波間干擾消除的效果;其物理原因可解釋為,在相同的載波頻率偏移下,能量愈高的接收信號造成的載波間干擾愈大,而使用最佳頻率校正值之頻率偏移校正器,則等同將不同路徑之載波頻率偏移,做了使載波間干擾能量為最小的調整。
由於頻域等化器須估測快速時變通道之突波響應以建立所需之干擾矩陣,相較而言,我們所提出的方法擁有較低的運算複雜度,而電腦模擬結果亦顯示此方法可達到可觀的效能。

In mobile OFDM systems, the small subcarrier spacing and the large Doppler Effect force us to face the problem of inter-carrier interference (ICI) seriously. The Doppler spread destroys the regularity among subcarriers and increases the lower bound of the probability of detection error, even without the disturbance of thermal noise or narrowband interference. The Doppler spread is like a system frequency offset but more difficult to deal with, since it consists of multiple frequency offsets originated from different paths. Conventional frequency synchronization techniques could not estimate such multiple frequency offsets well. Therefore, different viewpoints of handling the corresponding problem should be taken.
In this thesis, we propose a new approach with low computational complexity to estimate multiple frequency offsets for mobile OFDM systems based on the channel model that is non-isotropic scattering, where the angles of incidence for most of replicas of the received signal are not far off. We present a theoretical analysis which indicates that such a channel situation can be numerically represented by the sum of Doppler shifts weighted by the variance of each path. By correcting this weighted sum, the effect of ICI can be mitigated to some extent. We treat the weighted sum as the system frequency offset and make some modifications of the frequency synchronization technique to estimate and then correct the weighted sum. Simulation results are given to demonstrate the effectiveness of the proposed approach.

摘要
誌謝
目錄
第一章 簡介
第二章 OFDM 基本原理
第三章 載波間干擾消除技術
第四章 效能評估
第五章 結論
附錄 論文英文本

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