Forum: GNU Radio LMS_DD_Equalizer Block

Hello,
I have recently started using GNU Radio to implement a channel equalizer
using LMS algorithm. I can not figure out what should I pass in the
Constellation Object filed of the LMS_DD_Equalizer block. Attached is 
and
example GRC flow graph, in which the propagation channel is assumed to 
be a
constant multiplier. I am trying to recover a QPSK signal at the 
receiver
end.

The documentation of the LMS_DD_Equalizer block does not clearly explain
what to do for the Constellation Objectm, based on my limited 
experience.
Would you please provide some guidance as to what to pass in the
Contellation Object field?

Thanks,
Hamad

On Fri, Mar 1, 2013 at 12:41 AM, Hamad Alsawaha <hamadsw@vt.edu> wrote:
>
> The documentation of the LMS_DD_Equalizer block does not clearly explain
> what to do for the Constellation Objectm, based on my limited experience.
> Would you please provide some guidance as to what to pass in the
> Contellation Object field?
>
>
>
> Thanks,
>
> Hamad

In the source code, look at gr-digital/python/qa_lms_equalizer. That
shows you how to create a constellation object that you can pass to
the LMS equalizer block. Basically, it's just:

const = digital.constellation_qpsk()
EQU = digital.lms_dd_equalizer_cc(4, gain, 1, const.base())

Note that we have to get the base class from the constellation object
to pass it through Python and the SWIG interface.

that constellation class is quite complex in that there's lots you can
do with it. Havin the QPSK constellation is a convenience, but you can
use this interface to create your own constellations as well. This
should get you started, though.

Tom