Conf. on Acoustics, Speech, and Signal Processing,
April 6-10, 2003, vol. V, pp. 97-100, Hong Kong, China.
Exploiting Symmetry in Channel Shortening Equalizers
Rick Martin (1),
C. Richard Johnson, Jr.
Ming Ding (2), and
Brian L. Evans (2)
(1) Department of Electrical and Computer Engineering,
Ithaca, NY 14850 USA
(2) Department of Electrical and Computer Engineering,
Engineering Science Building,
The University of Texas at Austin,
Austin, TX 78712-1084 USA
ADSL Research at Cornell -
at UT Austin
Time-domain equalization is crucial in reducing inter-carrier and
inter-symbol interference in multicarrier systems. A channel shortening
time-domain equalizer (TEQ), which is a finite impulse response (FIR)
filter, placed in cascade with the channel produces an effective impulse
response that is shorter than the channel impulse response. We show that
finite length minimum mean squared error (MMSE) and maximum shortening SNR
(MSSNR) TEQs are approximately symmetric, and infinite length MSSNR TEQs
with a unit norm TEQ (UNT) constraint are exactly symmetric. A symmetric
TEQ halves FIR implementation complexity, enables the frequency-domain
equalizer and TEQ to be trained in parallel, and exhibits only a small
loss in bit rate over non-symmetric TEQs. In addition, a symmetric
MSSNR-UNT TEQ reduces training computational complexity by a factor of 4
and doubles the length of the TEQ that can be designed.
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