on Global Communications Conf.,
Dec. 1-5, 2003, vol. 4, pp. 2146-2150, San Francisco, CA USA.
Minimum Intersymbol Interference Methods for
Time Domain Equalizer Design
Ming Ding (1),
Brian L. Evans (1),
Martin (2), and
C. Richard Johnson, Jr. (2)
(1) Department of Electrical and Computer Engineering,
Engineering Science Building,
The University of Texas at Austin,
Austin, TX 78712-1084 USA
(2) Department of Electrical and Computer Engineering,
Ithaca, NY 14850 USA
at UT Austin -
ADSL Research at Cornell
During initialization, discrete multitone receivers train a time
domain equalizer (TEQ) to shorten the channel impulse response to
a preset length, v+1. Arslan, Kiaei, and Evans report a
Minimum Intersymbol Interference (Min-ISI) method for TEQ design.
Min-ISI TEQs give the highest bit rates among single-FIR TEQs
amenable to real-time implementation on programmable fixed-point
digital signal processors (DSPs). The Min-ISI method, however,
has several disadvantages: (1) sensitivity to transmission delay,
(2) inability to design TEQs longer than v+1 taps, and (3) sensitivity
to the fixed-point computation in the Cholesky decomposition.
In this paper, we develop an alternate Min-ISI cost function, from
which we derive (1) a fast search method for the optimal transmission
delay, (2) extensions to design arbitrary-length Min-ISI TEQs, and
(3) an iterative Min-ISI method. The iterative Min-ISI method avoids
Cholesky decomposition, designs arbitrary length TEQs, and
achieves the bit rate performance of the original Min-ISI method.
Questions and Answers
"I was trying to implement the adaptive min-ISI method from
your paper, titled 'Min-ISI methods for TEQ design' for the
upstream ADSL channel. Hoever [However], I find using the
adapive [adaptive] min-ISI method, I am obtaining complex
values for the equalizer taps."
"You should be able to get real-value results.
I think you should carefully check your gradient.
The cost function matrix is complex-valued, hence, the
gradient is a little bit different formed. Look at equation (12),
X is hermitian, [and] X+X' should give you real values."
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