Nonlinear blind equalization schemes using complex-valued multilayer feedforward neural networks

作     者：You, C Hong, D 

作者机构：Yonsei Univ Dept Elect Engn Seoul 120749 South Korea 

出 版 物：《IEEE TRANSACTIONS ON NEURAL NETWORKS》 (IEEE Trans Neural Networks)

年 卷 期：1998年第9卷第6期

页      面：1442-1455页

核心收录：

基　　金：National Research Foundation of Korea  NRF  (01-E-0840) 

主　　题：blind equalization complex backpropagation algorithm complex-valued activation function complex-valued multilayer perceptron feedforward neural network M-ary QAM signal neural equalizer nonlinear effect 

摘      要：Among the useful blind equalization algorithms, stochastic-gradient iterative equalization schemes are based on minimizing a nonconvex and nonlinear cost function, However, as they use a linear FIR filter with a convex decision region, their residual estimation error is high. In this paper, four nonlinear blind equalization schemes that employ a complex-valued multilayer perceptron instead of the linear filter are proposed and their learning algorithms are derived. After the important properties that a suitable complex-valued activation function must possess are discussed, a new complex-valued activation function is developed for the proposed schemes to deal with QAM signals of any constellation sizes. It has been further proven that by the nonlinear transformation of the proposed function, the correlation coefficient between the real and imaginary parts of input data decreases when they are jointly Gaussian random variables. Last, the effectiveness of the proposed schemes is verified in terms of initial convergence speed and MSE in the steady state. In particular, even without carrier phase tracking procedure, the proposed schemes correct an arbitrary phase rotation caused by channel distortion.