Re: step size selection for LMS algorithm

On Thu, 08 May 2008 12:11:10 -0500, "cpshah99"
<cpshah99@xxxxxxxxxxxxxx> wrote:

Hi All

I have implemented Adaptive Decision Feedback Equaliser using LMS
Algorithm. Now I am using 4-QAM Modulation scheme.

In the training mode, step size for feedforward filter is 0.01 and for
feedback filter is 0.003. And in decision directed mode the step size
for
feedforward filter is 0.001 and for feedback filter is 0.003. I have
got
these values after playing thru different values.

Now if I change the feedforward filter step size from 0.01 to 0.001 in
training period and rest of the setup is same then I am getting big
difference in terms of BER performance.

So, is there any perticular method to select step size?

It's always a good idea to gear shift instead of fixed step size.
There are multitudes of variable step size algorithms but a simple
divide by 2 at constant intervals almost always work so there is no
need for anything more sophisticated (again almost always). Of course
you need to remember to stop at a minimum step size which is decided
by your coefficients' dynamic range and the time-variability of your
channel.

%%%%%

HI

Can you please explain what gear shifting and divide by 2 at constan
intervals?

chintan
.