臺灣博碩士論文加值系統

在本論文之中，我們在正交分頻多工系統架構下，提出一個將傳送信號做前置編碼的方法，此前置編碼的方法使用一組在頻域與時域皆等振幅的正交碼。針對此正交碼的特性，我們提出一個新的半盲式通道估測器。有別於傳統通道估測器必須使用大量領航信號的缺點，半盲式通道估測器將減少領航信號的使用量，因此可以大幅提高資訊傳送速率。在我們提出的方法之中，僅需在傳送端之任意子載波上使用一個領航信號即可估測出所有通道的頻率響應，並且可以避免在無領航信號的子載波上，使用內插法所造成的估測誤差。為了降低估測誤差與提高系統表現，我們也推導了此估測器的正規化均方誤差，並針對其中數個重要的參數做分析，找出參數對系統的影響。我們在電腦模擬中，除了驗證估測器之正規化均方誤差的正確性外，並找出適合此系統的設定參數。在比較過兩個文獻中已提出的方法後，確定我們所提出的系統架構與通道估測器，可以使系統擁有較低的位元錯誤率。

In this thesis, a precoding scheme is proposed for channel estimation in orthogonal frequency-division multiplexing (OFDM) systems. The precoding scheme utilizes a special code matrix before the inverse fast Fourier transform (IFFT) at the transmitter. The row vectors of the matrix have constant amplitudes in both time domain and frequency domain. With the prcoding scheme, a semi-blind channel estimation method is proposed by using the characteristics of the row code sequences. In the proposed scheme, the channel frequency responses of all sub-carriers can be obtained by using only one pilot sub-carrier, and the proposed architecture can not only increase the data rate, but also avoid interpolation error in channel estimation. In addition, the normalized mean square error (NMSE) function is derived and parameters are optimized to improve system performance. The proposed precoding architecture and channel estimation scheme are shown to have better performances in bit error rate by conducting computer simulation experiments.

目錄
目錄..........................................................................................................IV
圖錄...........................................................................................................V
第一章 導論............................................................................................1
1.1 研究動機..............................................................................................1
1.2 論文架構..............................................................................................2
第二章 正交分頻多工系統之簡介與傳統通道估測之方法................3
2.1 OFDM系統之架構與性質..................................................................3
2.2 常用的通道估測演算法.....................................................................12
第三章 事前正交邊碼之半盲式通道估測架構..................................19
3.1 雙域等振幅序列.................................................................................19
3.2 半盲式通道估測器.............................................................................21
第四章 NMSE效能分析與還原接收信號..........................................28
4.1 接收訊號與還原.................................................................................28
4.2 NMSE效能分析.................................................................................29
第五章 模擬結果與討論......................................................................32
第六章 結論與未來工作......................................................................43
附錄 A.....................................................................................................45
參考文獻..................................................................................................49


圖目錄
圖2.1：(a)非重疊多載波通道調變技術之頻譜圖(b)正交分頻多工系統通道調變技術之頻譜圖....................................................................................................................4
圖2.2：傳統正交分頻多工系統發射機架構...............................................................5
圖2.3：傳統正交分頻多工系統接收機架構...............................................................5
圖2.4：(a) 信號通過S/P前之區間長度 (b)信號通過S/P後之區間長度..............6
圖2.5：OFDM系統輸出端資料轉換方式..................................................................7
圖2.6：OFDM系統接收端資料轉換方式..................................................................8
圖2.7：子載波間的頻譜關係......................................................................................9
圖2.8：保護區間造成載波間正交性失去示意圖....................................................10
圖2.9：OFDM符元之循環字首(CP)示意圖............................................................11
圖2.10：加入循環字首後子載波間的正交性關係..................................................11
圖2.11：兩種常見的領航訊號排列 (a)塊型排列 (b)梳型排列.............................20
圖3.1：自相關函數數值解........................................................................................20
圖3.2：互相關函數數值解........................................................................................21
圖3.3：通道估測方塊圖............................................................................................24
圖3.4：半盲式事前編碼估測器方塊圖……………...….........................................27
圖4.1：碼際間權重對一完美正交碼產生的干擾....................................................30
圖5.1：在兩種最低通道增益-16.5與-20.0dB下三種不同領航信號能量4, 16, 20的NMSE值..................................................................................................................33
圖5.2：在兩種最低通道增益-16.5與-20.0dB下三種不同領航信號能量4, 16, 36的BER值.....................................................................................................................34
圖5.3：在不同領航信號能量下BER與NMSE之關係圖(領航信號能量間距較大，能量範圍1~20)…...............................................................................................….....35
圖5.4：在不同領航信號能量下BER與NMSE之關係圖(領航信號能量間距較小，能量範圍1~10.75)….............................................................................................…..36
圖5.5：在不同領航信號能量下NMSE表示圖…...................................................36
圖5.6：在不同領航信號能量下BER表示圖...........................................................37
圖5.7：訓練符元與半盲式通道估測之NMSE值比較…..…..................................38
圖5.8：OFDM符元累積數之數學分析與模擬結果應證……………………........38
圖5.9：OFDM通道數目變化之數學分析與模擬結果應證....................................39
圖5.10：三種通道估測在通道增益最低下之-16.5dB之NMSE值........................40
圖5.11：三種通道估測在通道增益最低下之-16.5dB之BER值...........................40
圖5.12：三種通道估測在通道增益最低下之-20.0dB之BER值...........................41
圖5.13：三種通道估測在通道增益最低下之-20.0dB之BER值...........................41

[1] Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY)
Specifications IEEE Standard 802.11a, Part 11, 1999.
[2] “Broadband Radio Access Networks (BRAN): HIPERLAN Type 2 technical
specifications Part 1—Physical layer ETSI DTS/BRAN030 003–1,” 1999.
[3] “Orthogonal Frequency Division Multiplexing,” U.S. Patent No.3, 488, 445, filed Nov. 14, 1966, issued Jan. 6, 1970.
[4] 潘積桂, “多調分碼多重接取系統結合碼域傳送多樣性之通道估測效能分析”國立中山大學通訊工程研究所碩士論文, 2004.
[5]R. van Nee and R. Prasad, OFDM for Wireless Multimedia Communications, Artech House Publishers, Boston, 2000.
[6] J. van de Beek, O. Edfors, M. Sandell, S. K.Wilson, and P. O. B