[Discuss-gnuradio] Re: gnuradio trellis

[Anastasopoulos Achilleas]

Toby,

for me the term "equalization" is equivalent to
"sequence detection in ISI channels".
If by "equalization" you mean "linear" or "decision feedback"
equalization this is another story.

I am not sure how the gr-trellis stuff will be useful to you if
you do not want to do sequence detection, but some sort of
suboptimal linear or decision-feedback equalization, unless you
want to use it only for the GMSK detection part...

If you tell me more specifically what system you are
working on (modulation type, channel, receiver processing)
I can give more specific comments.

On Thu, 28 Sep 2006, Toby Oliver wrote:

> Achilleas,
>
> Okay. I am primarily interested in the equalization for the time being,
> but I can see it would seem to make a lot of sense to create the
> sequence detection as well.
>
> In terms of making the isi lookup table for multidimensional
> modulations, whats the best way to go about it? Is there any published
> literature on this that I could base it on?
>
> Kind Regards,
> Toby
>
> Anastasopoulos Achilleas wrote:
> > Oliver,
> >
> > You are right:
> > Trellis implementation supports multi-dimensional constellations etc
> > (through the metric calculation block abstraction, etc), however,
> > in the examples and the supporting fsm_utils.py files
> > I have not included support for GMSK, and the automatic
> > generation of lookup tables for ISI channels is for-one dimensional
> > modulations.
> > I think the extension should be straightforward and I'll be glad
> > to help you in this.
> >
> > May I suggest you separate the task into two subproblems for reasons
> > of usability by others:
> >
> > 1) GMSK sequence detection in AWGN channels
> > (which is a modulation with memory and in theory requires Viterbi
> > even in the absense of ISI),
> > and
> > 2) GMSK equalization (ie, GMSK + ISI channel + noise -> Viterbi)
> >
> > For 1) a modification of test_tcm.py is required and hopefully
> > an "automated" way to project any given GMSK modulation to its
> > N-dimensional components; maybe a python implementation of
> > the Gram-Schmidt (QR decomposition) algorithm...
> >
> > For 2) a modification of the test_viterbi_equalization.py or
> > test_viterbi_equalization1.py is required together with
> > generalizing the code in fsm_utils.py to generate the lookup table
> > for multi-dimensional modulations.
> >
> > best,
> > Achilleas
> >
> > On Wed, 27 Sep 2006, Toby Oliver wrote:
> >
> > > Achilleas,
> > >
> > > I hope you don't mind me emailing you, but I have just been having a
> > > look at your gnuradio trellis code which is very cool. In fact I was
> > > looking to try it out as an equalizer on some GMSK signals but it seems
> > > the make_isi_lookup in fsm_utils currently only supports one-dimensional
> > > modulations. Am I right in assuming the I will need to extend this for a
> > > GMSK signal? Or am I missing something?
> > >
> > > Thanks for adding this to Gnuradio, its a really useful (and incredibly
> > > flexible) addition.
> > >
> > > Kind Regards,
> > > Toby