單載波區塊傳送系統在多重路徑快速衰退通道下，除了受到符元間干擾之外，更會面臨虛擬載波之間的干擾；若仍使用在非時變通道下之頻域等化器將會導致嚴重的錯誤，此乃因為未考量虛擬載波之間的干擾之故。文獻中針對時變通道常用的等化技術為時域下最小均方誤差之線性等化器和最小均方誤差之連續干擾消除；兩者在錯誤率效能比較之下，後者擁有較低的錯誤率，但複雜度遠高於前者。
本論文希望可以在錯誤率及複雜度之間取較佳之平衡，我們將非時變通道下具有低複雜度的迭代區塊決策回授等化器延伸至多重路徑快速衰退通道。我們假設理想回授決策信號以推導在多重路徑快速衰退通道下的等化係數，但在模擬時我們則採用實際決策信號回授。模擬結果顯示我們提出的方法和最小均方誤差之線性等化器比較，僅須要再付出少許的複雜度即可以改善系統的錯誤率效能；和最小均方誤差之連續干擾消除比較，雖然我們有較高的錯誤率，但有較低的複雜度。

In doubly-selective channels, single-carrier block transmission suffers from not only inter-symbol interference (ISI) but also virtual inter-carrier interference (virtual ICI) because channel variation within a transmitted block can no longer be neglected. In this case, the detection performance deteriorates considerably if the equalizer does not account for time selectivity. In the literature, equalization algorithms that cope with time-varying channels include time-domain minimum mean squared error linear equalizer (MMSE-LE) and minimum mean squared error successive interference cancellation (MMSE-SIC). The latter has a better error-rate performance, but the former has a much lower complexity. In hopes of achieving a better trade-off between performance and complexity, we extend the low-complexity iterative block decision feedback equalizer (IBDFE), originally designed for frequency-selective channels only, to doubly-selective channels. To deal with the virtual ICI, the matrix feedback filter is adopted. We assume correct decisions to derive the equalizer coefficients; however, we feed back the actual decisions in simulations. Simulation results show that the proposed algorithm achieves a better performance than MMSE-LE with only a slight increase in complexity. Compared with MMSE-SIC, the proposed algorithm has a poorer performance, but a much lower complexity.

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