[Discuss-gnuradio] Re: gnuradio trellis

[Anastasopoulos Achilleas]

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