TIME-VARIANT EQUALIZATION USING A NOVEL NONLINEAR ADAPTIVE STRUCTURE

In much of the work which has been performed in the area of adaptive e qualization over the last 30 years there has been a concentration of e ffort on systems which are a priori unknown but time invariant (or, at least only slowly variant with time). In certain key applications, mo st notably in digital mobile communications, this assumption of time i nvariance is not realistic. It is therefore important to focus on the particular requirements placed on adaptive equalizers in this sort of challenging environment. This paper begins by examining the limitation s of classical linear equalizers in the time-variant environment. A no vel, non-linear, filter architecture which is designed to take advanta ge of the time-variant channel is then proposed. Two key points relati ng to this structure are that it has a complexity comparable to the st andard linear forms and it only requires to be adapted using a basic s tochastic gradient algorithm. Computer simulation studies are presente d which demonstrate the ability of this structure to produce enhanced performance (in terms of bit error rate) across a range of fast-fading channel conditions when compared to standard linear equalizers. (C) 1 998 John Wiley & Sons, Ltd.