Forum: GNU Radio Equalization class help

4eff8471dd77455a25564f9df9b2bd2e?d=identicon&s=25 bob wole (Guest)
on 2014-05-12 12:00
(Received via mailing list)
I want to work on equalization for ISI removal due to multipaths for
burst
frequency shift keying system. I found equalizer class in gnruadio, I
want
to know if somebody used cma_equalizer for the task with success or if I
can use it for equalization of burst frequency shift keying system
before
continuing with it?


Thanks
C539637020fd56193dd6daec746c4a84?d=identicon&s=25 Tom Rondeau (Guest)
on 2014-05-12 15:03
(Received via mailing list)
On Mon, May 12, 2014 at 5:59 AM, bob wole <bnwole@gmail.com> wrote:

> Bob
>

It'll conceivably work, but the challenge with the CMA equalizer (and
the
LMS-DD equalizer as well) is the long convergence time. Between every
burst, you're going to lose tracking of the taps, so you might want to
think of a way to shut down the tap update loop when you're not
receiving a
packet (which involves knowing when that's happening in time to send the
info to the equalizer). For starters, just use a few taps in the
equalizer
and a gain higher than you would expect to see if you can get it to
converge to "close enough" early in the burst.

Tom
4eff8471dd77455a25564f9df9b2bd2e?d=identicon&s=25 bob wole (Guest)
on 2014-05-12 16:44
(Received via mailing list)
Thanks for your reply Tom. Could I have some  more explanation on it?
if a
training sequence at start of each burst could help in fast convergence
for
burst modem?

--
Bob
C539637020fd56193dd6daec746c4a84?d=identicon&s=25 Tom Rondeau (Guest)
on 2014-05-13 15:18
(Received via mailing list)
On Mon, May 12, 2014 at 10:43 AM, bob wole <bnwole@gmail.com> wrote:

> Thanks for your reply Tom. Could I have some  more explanation on it?  if
> a training sequence at start of each burst could help in fast convergence
> for burst modem?
>
> --
> Bob
>

Time-domain equalizers just generally take a bit of time to converge,
and
when there's no signal, it will try to equalize the noise floor, so
every
burst starts it fresh. It's certainly possible that the training
sequence
may be enough, and tuning the length of the equalizer and gain may help.

Also, if you know the training sequence, you could potentially use that
to
get calculate the channel. Look at the correlate_and_sync block, which
uses
a known training sequence to estimate the timing and phase of a burst.
That
could be modified to also estimate the channel and initialize your taps.

Tom
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