時變通道環境下LTE下行鏈路系統通道估測與等化之改善

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姓名

吳信穎(Hsin-Ying Wu) 查詢紙本館藏

畢業系所

通訊工程學系

論文名稱

時變通道環境下LTE下行鏈路系統通道估測與等化之改善
(Improvement of Channel Estimation and Equalization for LTE Downlink System in Time-Varying Channel Environment)

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摘要(中)

LTE(Long Term Evolution)系統是由3GPP(3rd Generation Partnership Project)所提出的第四代行動通訊系統。LTE下行鏈路採用了OFDMA(Orthogonal Frequency Division Multiple Access)系統，它是根據OFDM(Orthogonal Frequency Division Multiplexing)系統演進而來，因此與OFDM面臨了相同的挑戰。其中最具挑戰性的問題之一是在隨著時間變化的通道環境中，而引起子載波間正交性被破壞及載波間干擾(Inter-Carrier- Interference，ICI)。此外，因通道會隨著時間變化的特性，而需要更多的參考訊號密集的分佈在時域的子載波上，以利於通道估測，卻使得頻譜效率大幅降低。
在本篇論文中，我們將提出LTE下行鏈路系統在時間變化的環境中，改善其通道估測的準確度，傳統的通道估測方式使用多項式擴展模型(P-BEM)可以直接實現在LTE下行鏈路系統中的參考訊號擺放方式，然而這些方法在時變通道的環境下，因頻域與時域上通道的變化使其性能大幅下降。在此篇論文中，我們提出了一種改進通道估測的方式，結合了資料直接決策(Data-Decision Directed)與多項式擴展模型(P-BEM)的機制，透過模擬來證明通道估測性能之改善。

摘要(英)

LTE (Long Term Evolution) system is the fourth generation mobile communication system proposed by the 3GPP (3rd Generation Partnership Project). In the down link, LTE system adopts Orthogonal Frequency Division Multiple Access (OFDMA) technique which is based on Orthogonal Frequency Division Multiplexing (OFDM) and therefore faces the same challenging problems. One of the most challenging problem is the channel estimation in the time-varying environments where the orthogonality between the subcarriers is destroyed and inter-carrier interference (ICI) is caused. Moreover the time-varying channel characteristic implies a denser pilot subcarriers distribution in time-domain when the simple pilot-aided channel estimation is applied, which incurs a decrease in spectral efficiency.
In this thesis, we tackle the channel estimation problem in time-varying environments specifically for LTE downlink system. Traditionally the channel estimation can be directly achieved with the polynomial basis expansion modeling methods (P-BEM) based on the pilot pattern specified in LTE downlink system. However, the performance of these methods degrades in time-varying environments due to the channel variation in both frequency domain and time domain. In this thesis, we propose an improvement method which incorporates data-decision directed mechanism with the P-BEM. The performance improvement is demonstrated through simulation with a cost in computation complexity.

關鍵字(中)

★ 通道估測
★ 下行鏈路
★ 渦輪碼

關鍵字(英)

★ Channel Estimation
★ Downlink
★ LTE
★ OFDMA
★ Turbo Code

論文目次

摘要.....................................................iv
ABSTRACT..................................................v
目錄......................................................vi
表目錄.................................................. viii
圖目錄.....................................................ix
第一章緒論..................................................1
1.1 簡介 ..................................................1
1.2 研究動機 ...............................................2
1.3 章節提要 ...............................................3
第二章LTE下行鏈路系統簡介 .....................................4
2.1 OFDM系統簡介............................................4
2.1.1 OFDM調變介紹..........................................4
2.1.2 OFDMA系統介紹........................................10
2.2 LTE結構介紹............................................12
2.2.1 LTE傳輸資源結構.......................................12
2.2.2 LTE系統分工模式.......................................14
2.3 實體層下行鏈路系統簡介 ...................................16
2.3.1 LTE下行通道與下行信號簡介...............................16
2.3.2 LTE下行鏈路通道編碼介紹................................18
2.3.3 LTE下行鏈路系統簡介....................................23
2.3.4 LTE下行鏈路傳輸參數....................................27
2.3.5 LTE常用通道模型.......................................27
第三章時變環境下通道估測與等化.................................28
3.1 時變通道簡介 ...........................................28
3.1.1 時變通道模型 .........................................29
3.1.2 線性近似通道 .........................................30
3.2 等效訊號模型 ...........................................31
3.3 載波訊雜比 ............................................34
3.4 通道估測與等化(CHANNEL ESTIMATION)......................36
3.4.1 最小平方通道估測(Least Square Channel Estimation).....36
3.4.2 通道頻率響應線性內插 ..................................37
3.4.3 頻域零値逼近法通道等化 .................................38
3.5 搜索式(SEARCH)頻域通道估測...............................38
3.6 多項式模型化(POLYNOMIAL MODEL-BASED)通道估測.............41
3.7 分段多項式(PIECEWISE POLYNOMIAL)時域通道估測..............44
第四章模擬結果與分析.........................................46
4.1 LTE下行鏈路模擬規格介紹..................................46
4.2 時變通道下LTE下行鏈路通道估測之效能.........................49
4.3 模型化通道估測參數模擬 ...................................57
第五章未來與展望.............................................60
附錄A.....................................................61
名詞解釋...................................................75
參考文獻...................................................76

參考文獻

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指導教授

陳逸民(Yih-Min Chen)

審核日期

2012-10-22

推文