臺灣博碩士論文加值系統

在區塊渦輪碼（Block Turbo Codes，稱BTC）解碼演算法中，對於解碼參數權重因子α及可靠因子β值均為隨著疊代的次數做靜態的設定，由於傳輸時通道具有時變性，這種以預先設定α，β值來參與解碼的方式，並非是一種最佳的估測，本文提出隨著解碼輸入與解碼輸出值的改變，動態的來估測α，β值。
區塊渦輪碼解碼演算法是一種利用反覆疊代解碼來改善解碼的效能，對於解碼運算時，大多設定八次為其所需解碼的半疊代次數。然而，在實際的訊息解碼中解碼疊代的次數是與訊息傳輸所經過的通道環境有關，當雜訊源較大的環境中即需較多的解碼疊代才能解出正確的訊息，而雜訊源較輕微的環境則僅需較少次的解碼疊代即可更正為正確的訊息。因此本文在傳統的區塊渦輪解碼器中，度量解碼器的輸入訊息量和輸出訊息量，分別比較其符號位元的改變情況來訂定停止疊代解碼的機制。經實驗證實，本文所提出的方法能有效地改善解碼疊代次數，在Eb/No =5dB的通道環境下可解省疊代次數達64%，而其解碼增益卻只有些微的損失。

In a general decoding algorithm of block turbo codes(BTCs), the weighting factor α and reliability factors β are fixed in each decoding iteration. However, for time-variant channels predefined α and β are not appropriate in BTC decoding. The thesis proposes a method to set the
values of α and β dynamically based on input and output values of the decoder.
BTC decoding algorithms use an iterative decoding procedure to achieve high bit error rate performance typically with eight half decoding iterations. However, the requirement of the number of decoding iterations
is related to the channel;i.e., the larger the noise is, the more number of iterations is required. Three novel stopping criterions are proposed in the thesis. Simulation results demonstrate that these proposed stopping criterions substantially reduce the number of decoding iterations. For example, about 64% iterations can be saved (on average) at
Eb/No=5dB without the noticeable loss of BER performance.

目錄
指導教授同意書…………………………………………………………I

口試委員會審定書……………………………………………………II

授權書…………………………………………………………………III

致謝……………………………………………………………………IV

中文摘要………………………………………………………………V

Abstract………………………………………………………………VI

第一章 序論……………………………………………………………1
1.1研究背景………………………………………………………1
1.2研究目的………………………………………………………2
1.3結果概敘………………………………………………………3
1.4論文架構………………………………………………………3

第二章 硬式與軟式解碼演算法簡介…………………………………5
2.1 高斯雜訊………………………………………………………8
2.2 硬式判斷………………………………………………………9
2.2.1 最大事後機率法則……………………………………9
2.2.2 最大概似機率法則……………………………………10
2.3 軟式判斷……………………………………………………11
2.4 硬式與軟式解碼演算法……………………………………12
2.4.1 硬式解碼演算法………………………………………13
2.4.2 軟式解碼演算法………………………………………13
2.5 硬式與軟式解碼效能之比較………………………………14
2.6 Chase演算法……………………………………………15
2.6.1 Chase-II解碼演算法……………………16
2.6.2 Chase-II演算法的解碼效能………………20

第三章 區塊渦輪碼……………………………………………………21
3.1 乘積碼………………………………………………………22
3.2 區塊渦輪碼…………………………………………………22
3.3 區塊渦輪碼之解碼效能……………………………………29

第四章 區塊渦輪碼效能改善之研究……………………………31
4.1 基於解碼前後的資訊量，動態估測α，β…………………31
4.2 利用解碼前後符號的改變量，制定停止疊代門檻…………33
第五章 結論與未來展望………………………………………………41
5.1結論……………………………………………………………41 5.2 未來展望………………………………………………………41

參考文獻………………………………………………………………43

圖目錄
圖2-1 數位通訊系統架構………………………………………………7
圖2-2 高斯雜訊之機率密度函數………………………………………8
圖2-3 接收訊號之機率密度函數………………………………………8
圖2-4 （7,4）漢明碼之硬式與軟式解碼演算法之效能比較………15
圖2-5 Chase演算法之幾何表示圖……………………………………16
圖2-6 Chase演算法之流程圖…………………………………………19
圖2-7 Chase演算法之解碼效能………………………………………20
圖3-1 乘積碼之架構圖………………………………………………22
圖3-2 渦輪區塊碼之區塊圖…………………………………………27
圖3-3 渦輪區塊碼之流程圖…………………………………………28
圖3-4 BTC(32,26,4)2在高斯通道環境下之解碼效能………………29
圖3-5 BTC(64,57,4)2在高斯通道環境下之解碼效能………………30
圖4-1 BTC為原始方法之效能， MI為本文所提出之方法…………32
圖4-2 加入HDA之區塊渦輪碼之流程區塊圖………………………36
圖4-3 BTC(32,26,4)2和加入停止機制之效能比較…………………37
圖4-4 BTC(64,57,4)2和加入停止機制之效能比較…………………37
圖4-5 BTC和加入停止機制所需疊代次數比較……………………38
圖4-6 BTC和加入停止機制所需疊代次數比較……………………38
表目錄
表4-1 比較在BTC和MI下，Eb/No相同時，其位元錯誤率
(BER)……………………………………………………………32
表4-2在BTC(32,26,4)2加入的停止機制所節省的疊代次數比較…39
表4-3在BTC(64,57,4)2加入的停止機制所節省的疊代次數比較…39

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