臺灣博碩士論文加值系統

隨著第三代個人行動通訊時代的來臨，資料在高速無線傳輸上的正確性更顯重要，先進的渦輪碼扮演解資料回復的重要角色。渦輪碼的解碼效能可以趨近於沈農極限，但運算複雜度太高卻也是渦輪碼的致命傷，所以以傳統維特比解碼為基礎的軟輸出維特比解碼便因此應用在渦輪碼上，因為軟輸出維特比解碼是以傳統維特比解碼為基本架構，所以運算複雜度較最大機率演算法(Maximum A-Posteriori, MAP )要少上許多，當然硬體實現上的速度也較快，相對的；效能上就不及最大機率演算法。因此，在不大量增加運算複雜度及考慮可行性的情況下，我們改進雙向軟輸出維特比演算法(Bi-directional SOVA)來增加效能。在經過模擬後，改良後的雙向軟輸出維特比演算法可以相當接近最大機率演算法的效能，最後我們將這個演算法實現在FPGA上，並且實際測量其解碼效能。

For the coming age of the third generation mobile communication system, the reliability of high-speed data transmission is more important. The performance of turbo code which can theoretically approach to the one of Maximum a-posterior (MAP) algorithm plays an important role in recovering information. However, the Achilles'' heel of Turbo code is the high computational complexity. SOVA (Soft-out Viterbi Algorithm) is a very good algorithm for using in turbo code because of its low computational complexity and it is based on the traditional Viterbi algorithm so its computational complexity would be considered as low as possible. Obviously, the implementation of SOVA could be easier than the MAP. Somehow, the performance of SOVA is relatively worth than the one of MAP. We consider a new algorithm that will not cause high computational complexity to improve the performance of SOVA. Therefore, we proposed the improved Bi-directional SOVA. Surprisely, the performance of Bi-directional SOVA could approach to the one of Log-MAP after simulation so it is a very efficient way to implement in hardware. We utilized the improved Bi-directional SOVA in FPGA and measured the performance indeed.

中文摘要 i
英文摘要 iv
誌謝 iv
目錄 iv
圖目錄 vi
表目錄 vii
第一章 簡介 1
第二章 渦輪編解碼及相關區塊介紹 3
2.1 渦輪編碼…………………………………………………………………………3
2.2軟資訊(Soft Imformation)交換與疊代(Iteration)……………………………6
2.3 渦輪解碼…………………………………………………………………………6
第三章 用於渦輪碼的迴旋解碼介紹 9
3.1 最大機率演算法(Max a-posteriori algorithm, MAP)…………………………9
3.2 指數最大機率演算法(Log-MAP)………………………………………………14
3.3 最大指數最大機率演算法(Max-Log-MAP)……………………………………15
3.4 軟輸出維特比演算法(Soft Output Viterbi Algorithm,SOVA)……………………20
3.5 用於渦輪碼之迴旋編碼效能比較………………………………………………26
第四章 軟輸出維特比演算法之改進方法介紹 30
4.1 改良式之軟輸出維特比演算法(Modified SOVA, M-SOVA)…………………30
4.2 雙向軟輸出維特比演算法……………………………………………………34
4.3 事後機率正規化………………………………………………………………37
4.4 具有量度因子的雙向軟輸出維特比演算法…………………………………43
第五章 軟輸出維特比演算法硬體實現之個別單元 46
5.1 比較-加法-選擇單元(CAS unit)………………………………………………46
5.2 暫存器交換單元（Register Exchange unit）…………………………………49
5.3 更新字串(Update Sequence)的計算……………………………………………50
5.4 可靠度更新單元…………………………………………………………………51
5.5 軟輸出維特比解碼器架構………………………………………………………52
5.6 雙向軟輸出維特比演算法之資料流程…………………………………………53
5.7模擬結果………………………………………………………………………56
5.8 合成與最後結果(Post simulation) ………………………………………………..58
第六章 結論 60
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