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Adaptive Equilization

Started by July 29, 2005
I'm looking at the block diagram on page 247 of "Adaptive Signal
Processing" from B.Widrow and S.D.Stearns.

Anyway, the block diagram shows an LMS filter in the center, and the
Quantizer on the bottom right.  The output of the Quantizer goes to a
subtraction element (which subtrats the LMS output from the Quantizer),
then the output goes to the  "Gate".

First, what is the output of the Quantizer? Is the output a 1 and -1
(or 0)?  This does not make sence to me since this variable will be
subtracted from the LMS output which cound be of any magnitude.

Second, what is the function of the "Gate"?  I know it's suppose to
provide an error signal to the LMS process, when it sees the center of
the pulse, but what does it do the rest of the time?

I've googled all over the place and I still haven't found anything
useful.  Thanks in advance for any help.

Jeff Stout

On 29 Jul 2005 09:33:31 -0700, jstout@ncon.com wrote:

>I'm looking at the block diagram on page 247 of "Adaptive Signal >Processing" from B.Widrow and S.D.Stearns. > >Anyway, the block diagram shows an LMS filter in the center, and the >Quantizer on the bottom right. The output of the Quantizer goes to a >subtraction element (which subtrats the LMS output from the Quantizer), >then the output goes to the "Gate". > >First, what is the output of the Quantizer? Is the output a 1 and -1 >(or 0)? This does not make sence to me since this variable will be >subtracted from the LMS output which cound be of any magnitude.
The output of the quantizer is your symbol space ie an instantenous decision which is the output closest to one of the symbols transmitted. So if your incoming symbols are -1, 1 then that's what the quantizer will give you most probably by saying that anything above 0 is +1 and anything below 0 is -1. Hopefully your adaptive equalizer will converge and the input to the quantizer will coalesce around these two points too (eye will open). If you have a multi-level signal, your quantizer will quantize to those level.