Pole-zero decision feedback equalization for the digital subscriberloop

摘要

A decision feedback equalizer (DFE) containing a feedback filterwith both poles and zeros is proposed for high-speed digitalcommunications over the subscriber loop. The feedback filter is composedof two sections; a relatively short finite-impulse-response (FIR) filterthat cancels the initial part of the channel impulse response, which maycontain rapid variations due to bridge taps, and a pole-zero filter thancancels the smoothly decaying tail of the impulse response. It is shownthat the feedback filter can be adapted using existinginfinite-impulse-response (IIR) adaptation techniques. Numerical resultsusing a simulated subscriber loop impulse response show that a feedbackfilter with two poles adapted via a simplified gradient algorithm canoffer significant improvement in mean squared error (MSE) (i.e., 3 to 4dB at a signal-to-noise ratio of 20 dB) relative to a conventional DFEof the same complexity