直序分碼多工系統在頻率選擇性衰減通道
之渦輪等化器及干擾抑制

在多重進接存取行動通訊系統上，如果通道為時變-多路徑衰減通道時，那麼符碼間干擾(inter-symbol interference)及多用戶之間的干擾(multiple access interference)是需要同時被考慮的。因為多路徑衰減通道通常會改變展頻碼的統計特性，並嚴重影響系統效能, 因此在接收端的設計，我們須設法有效的克服多路徑衰減通道的影響，並將多用戶之間的干擾抑制到最低。在本篇論文中，我們結合了自適性相關器(adaptive correlator) 和渦輪解碼器(turbo decoder)來當成一個近似於渦輪等化器(turbo equalizationlike) 的接收機來達到接收器效能的提升。在一般的渦輪等化器設計中，通常使用軟式輸入-軟式輸出(soft input soft output,SISO)等化器來當成通道等化器，但是由於其複雜度太高，所以近年來提出了利用線性濾波器及最小平方誤差(MMSE)的演算法來改善軟式輸入-軟式輸出等化器的複雜度。但又因為最小平方誤差需要計算自相關函數(auto-correlation)，交互關連函數(corss-correlation)，及反矩陣等複雜的數學運算，因此在本篇論文中，使用了自適性演算法(adaptive algorithm)來降低計算上的困難，並且結合了渦輪解碼器當成接收機的架構來提升系統效能。

關鍵字

渦輪等化器；自適性相關器

並列摘要

In CDMA mobile communication system with time-varying multipath fading channel, both intersymbol interference (ISI) and multiple access interference (MAI) must be considered. The multipath fading channels usually change the characteristics of the spreading codes, and severely degraded the system performance. Therefore, in the receiver design, we should try to overcome the effect of multipath fading channel, and suppress the multiple access interference. In this thesis, we combine the adaptive correlator [2] [3] and turbo decoder as a turbo equalization-like receiver to improve the system performance.In the design of turbo equalizer [4] [5], the soft input soft output (SISO) equalizer is usually used as the channel equalizer. In recent years, because of the high complexity of SISO equalizer, there are many scholars used the linear filter and optimum minimized-mean-square-error (MMSE) criterion instead of soft-input soft-output (SISO) equalizer to save the complexity. For MMSE criterion, we should compute the auto-correlation function, corss-correlation, and inversed matrix, ect, . Therefore, in the thesis, we use the adaptive algorithm to reduce the complexity of tedious mathematical operations, and combine adaptive correlator with the turbo decoder to improve the performance of CDMA system.

並列關鍵字

adaptive correlator ； turbo equalization ； LMS

參考文獻

[1] Fang-Biau Ueng and Li-Der Jeng, ”Adaptive Receiver for DS/CDMA

in direct sequence spread spectrum communication ”,Military Communications

[4] Koetter, R.; Singer, A.C.; Tuchler, M.; Turbo equalization, Signal Processing

Magazine, IEEE Volume 21, Issue 1, Jan. 2004 Page(s):67 - 80

[5] Tuchler, M.; Koetter, R.; Singer, A.C.; ”Turbo equalization: principles

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直序分碼多工系統在頻率選擇性衰減通道之渦輪等化器及干擾抑制

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