ADAPTIVE EQUALIZATION OF A NONLINEAR CHANNEL BY MEANS OF GAUSSIAN RADIAL BASIS FUNCTIONS

This paper proposes a preset adaptive equalizer which effectively equa lizes the distortion caused by channel nonlinearities. This equalizer closely approximates an optimal equalizer by using the Gaussian radial basis function (RBF) expansion, The RBF expansion consists of a nonli near transformation using the distribution of a number of vectors, cal led centers, and a linear combination of the signals after transformat ion. The behavior of the RBF expansion largely depends on the choice o f the centers used. in the nonlinear transformation and on their varia nces. It is first shown that the received signal vectors and their var iances can be estimated from the one-to-one correspondence of the tran smitted signal vectors and received signal vectors. It is next shown t hat when the estimated received signal vector and its variance are use d as the center and variance for the nonlinear transformation of RBF e xpansion, the capabilities of the RBF expansion are sufficiently manif ested. Moreover, the one-to-one correspondence of the transmitted sign al vectors and received signal vectors allows effective setting of the optimum values of parameters for the linear combiner used in the RBF expansion. We show by computer simulation that the proposed equalizer can achieve the same capabilities as an optimum equalizer with a small er amount of test data and will have a smaller bit error rate than con ventional adaptive equalizers. (C) 1997 Scripta Technica, Inc.