Equalization of digital subscriber lines under dynamic channel conditions

  • Authors:

  • Martin Glavin;Edward Jones

  • Affiliations:

  • Department of Electronic Engineering, National University of Ireland, Galway, Ireland;Department of Electronic Engineering, National University of Ireland, Galway, Ireland

  • Venue:
  • Signal Processing
  • Year:
  • 2004

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Abstract

In high-speed communications systems the task of channel equalization can be quite demanding. One of the most common and most powerful equalization algorithms is the decision feedback equalizer (DFE). In certain cases though, the DFE is not powerful enough to give the required performance margin on its own, and a forward error correction (FEC) scheme must be employed to give an extra boost in performance. The introduction of the FEC in itself creates problems for the DFE, which is usually compensated for by the use of a precoder. In steady state, this does not affect the overall performance of the system, but in a situation where the channel is subject to change, the precoding scheme runs into difficulty because a fixed precoder cannot compensate for the change.This paper describes a modification to the conventional fixed precoder that allows the precoder to adapt slowly in a dynamic channel environment. Also shown here is an enhancement of this adaptive precoder that increases the speed of precoder adaptation. The technique is applied to digital subscriber line (DSL) transmission at 1.544 Mbit/s, using coded 16-PAM modulation. Simulations show that the proposed techniques are very effective in enabling rapid recovery of optimum performance levels following a severe change in the channel.