Abstract
We study the equalization procedure in discrete
multitone (DMT)-based systems, in particular, in DMT-based ADSL
systems. Traditionally, equalization is performed in the time
domain by means of a channel shortening filter. Shifting the
equalization operations to the frequency domain, as is done in
per-tone equalization, increases the achieved bitrate by 5–10%.
We show that the application of the turbo principle to per-tone
equalization can provide significant additional gains. In the
proposed receiver structure, referred to as a “turbo-per-tone
equalization” structure, equalization and decoding are performed
in an iterative fashion. Equalization is done by means of a
linear minimum mean squared error (MMSE) equalizer, using
a priori information. We give a description of an
efficient implementation of such an equalizer in the per-tone
structure. Simulations show that we obtain a bitrate increase of
12–16% compared to the original per-tone equalization-based
receiver structure.