但是當傳輸位元率提高時,例如超過2400 bits時,ISI的問題會變嚴重,這時就需要使用自適應性頻道等化器(Adaptive Channel Equalizer)來克服通道失真(Channel Distortion)的問題。
Adaptive Equalizer當見的實現方式是使用自適應性有限脈衝響應濾波器(Adaptive FIR Filter),其係數採用LMS演算法(Least-Mean-Square Algorithm, 最小均方演算法)進行調整,以克服通道失真。LMS演算法是一種隨機梯度演算法(Stochastic Gradient Algorithm)。
參考資料:
Adaptive equalizer (Wikipedia)
Stochastic gradient descent (Wikipedia) (隨機梯度下降)
Least mean squares filter (Wikipedia) (屬於一種Stochastic Gradient Algorithm)
Recursive least squares filter (Wikipedia)
Haykin, S. S. (2014). Adaptive filter theory. 5th edition, Pearson Education. pp 40-43, 468-471.
Ingle, V. K., & Proakis, G. J. (2014). Essentials of Digital Signal Processing using MATLAB®. CENGAGE Learning, pp 603-606.