High stability fast tracking adaptive equalizer for use with time varying communication channels

Abstract

An adaptive equalizer capable of tracking rapid channel variations while maintaining high stability and low jitter, and a receiver constructed therefrom. A novel feature of the invention is that is that the equalizer is sectioned, that is constructed from a plurality of feed-forward sections and decision-feedback sections, where these sections comprise a cascade of an adaptive linear filter and an adaptive multiplier. This structure is effective at combating rapid channel variations, which are a result of delay variations of the reflections of the signal, e.g., airplane flutter, without sacrificing the stability and the accuracy of the equalizer even in cases where the equalizer has a large number of taps. The different equalizer sections may have different step size parameters. A controller monitors the channel variations and adjusts the step size parameters of each section accordingly. The controller increases the step size of the equalizer sections that are able to compensate for the variation of the channel and does not increase the step sizes of the other sections. This allows the equalizer to combat rapid channel variations without sacrificing stability and accuracy. The present invention is particularly suitable to high speed wireless RF digital communications applications, e.g., to DTV broadcast applications, where the equalizer is characterized by a large number of taps and the signal is subject to rapid time varying reflections due to movement of objects such as cars and airplanes.