單載波系統中採用單一字元之適應性決策回授等化技術

Adaptive Decision-Feedback Equalization for Unique-Word Based Single Carrier Systems

陳俊杰(Chun-Chieh Chen)

指導教授 ： 王晉良

國立清華大學/電機資訊學院/通訊工程研究所/碩士(2006年)

https://doi.org/10.6843/NTHU.2006.00533

摘要

在採用單一字元之單載波(unique-word based single carrier (UW-SC)) 系統中，我們可以像正交分頻多工 (OFDM) 系統一樣使用低複雜度且有效的頻域等化技術來消除非時變環境中多重路徑干擾 (multipath interference)所造成的符距間干擾 (ISI)，使得此系統對於頻率選擇衰減 (frequency selective fading)非常強健。但是都卜勒效應同時也造成了時間選擇衰減 (time selective fading)，這破壞了原本通道在頻域上的正交特性，使得原先的單閥門等化器不再能夠有效的使用。因此必須再提出其他的方法來抵制時變環境中的符距間干擾。
線性最小均方誤差 (linear minimum mean square error) 法則提供了一個有效的解決方案卻需耗費相當高的複雜度。在這篇論文中，我們利用通道在時域上的稀疏特性提出了一個低複雜度的區塊最小均方誤差 (block MMSE) 等化器降低線性最小均方誤差方法的複雜度。利用先前提出的等化器在時變通道的影響下所獲得的時間分集 (time diversity)，我們可以使用平均法改善最小均方誤差等化器的效能。在前面兩個方法的基礎下，同時考慮此系統所提供的單一字元資訊，最後可以提出一個適應性決策回授等化器 (adaptive decision feedback equalizer) 的架構，再進一步消除前一級等化器所殘留下來的符距間干擾並有效地降低位元誤差率 ( bit error rate)。
最後，從電腦模擬結果以及表格分析，我們可以看出此論文提出的方法不僅有效地消除符距間干擾，擁有相當於線性最小均方誤差的位元錯誤率而且相較於線性最小均方誤差以及其他現存的消除法，此等化器還大幅度降低了複雜度。可以說是一個非常實用的設計。

關鍵字

決策回授等化器 ； 雙重選擇通道 ； 單一字元 ； 單載波

並列摘要

Unique word based single carrier (UW-SC) systems have been proposed as an alternative to orthogonal frequency division multiplexing (OFDM) systems. UW-SC not only avoids the peak-to-average power ratio problem that plagues OFDM but also supplies the known information of unique words for additional purposes. Although UW-SC is very robust to frequency selective fading in a multipath environment, it is sensitive to the time selective in wireless channel that corrupts the orthogonality of the channel matrix in the frequency domain.
In this thesis, we first derive a low-complexity time-domain block minimum mean-squared error (MMSE) solution as a feedforward filter for UW-SC systems in the presence of inter-symbol interference (ISI) caused by doubly selective channel. For residual ISI reduction, we also present a decision feedback filter after the feedforward filter to form a new decision feedback equalizer adapted by unique word. Simulation results and complexity comparisons are given to show that the proposed method has considerably satisfactory performance and lower complexity than linear MMSE and iterative MMSE.

並列關鍵字

Decision Feedback Equalizer (DFE) ； Doubly Selective Channel ； Unique Word ； Single Carrier

參考文獻

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