Re: equalizer output issue - eqout.jpg (0/1)

Hi everyone,
I'm working on an LMS adaptive filter which is behaving in somewhat of
an unexpected way. The attached image shows the histogram of the
equalizer output after convergence; my slicer thresholds are at 0.5
and -0.5 (ie anything above 0.5 is sliced to 1, anything below -0.5 is
sliced to -1 and anything in between is sliced to 0; this is a 3 level
code.) Then I use an error generated from this sliced value and the
actual output to adapt the filter.
As one can see the mean of the outputs close to 1 and -1 are not
really 1 and -1 which is what I expected. Also the distributions of
the outputs around 1,-1 are not really symmetric; again something I'd
expect to see. Obviously what I am trying to do is to make the
histogram more coalesced around 1,0,-1 to get a more distance between
decision points.
I know the question is a little vague without a lot more detail but
does anyone have any comments on why this might be happening?

Thanks.

Muzaffer Kal

Muzaffer,

Two things: (i) Your image is not visible, nor is there a way to post an
image to a post here. Maybe you can post a link to it. (ii) The
distribution of your quantized values depends on the pdf of the input. If
you had an input that is uniformly distributed between [-1.5, 1,5], then
you would get equally likely quantized values of {-1,0,1} using -0.5 and
0.5 as slicing points.

Your question relates to the problem of quantization. If you know the
input pdf and you can define a criterion for the output, such as obtaining
a uniform distribution or minimizing MSE, then you can get adjust the
quantized values and/or slicing points to meet this objective.

Hope this helps,

Emre

.

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