Re: [Discuss-gnuradio] channel coding questions

[Ben Reynwar]

On Fri, Feb 11, 2011 at 12:59 PM, Achilleas Anastasopoulos
<address@hidden> wrote:
> Ben,
>
>
> I have a simple example of turbo coding/decoding (i think it is a sccc) in
> the examples section of gr-trellis. It is SLOW!
> I don't think there is any particular reason other than you are essentially
> have to run 2 siso blocks per iteration, ie, roughly
> 4 VA's per iteration (recall forward/backward pass)...
> The comment i made about buffering is from my experience:
> You can always get a better performance if you combine the functionality of
> multiple gnuradio blocks into one gnuradio block...
>
>
> Regarding suboptimal receivers, I don't have any intention of writing code
> for them, but if anyone is willing to work seriously on that i can help
> (maybe an undergrad student project for the summer...)
> Similarly, for a turbo decoding hierarchical block: it is trivial to put
> together siso blocks and do it (the  code is essentially there: see the
> python code in the examples). I can think of an sccc and a pccc block
> whereby you define the 2 constituent FSMs (or even more), an interleaver
> structure, and the number of iterations; that's all there is to it.
>
> Regarding integration with the "constellations" class i think it is a
> wonderful idea. When I was writing gr-trellis I thought of constellations as
> arbitrary one-dimensional look-up tables with n-dim entries. Repackaging the
> "metrics" code to use constellations would be great.
> YES, I believe that the "constellations" class has to be general enough to
> include n-dimensional constellations. What if you want to implement 4-FSK,
> or even arbitrary CPM (I am currently working on that).
> Also, there are trellis-codes that output 2 QPSK (or 2 8PSK) symbols at
> every step and having these constellations as 1 2D complex constellation
> makes integration with gr-trellis very easy...
>
> Achilleas
>

I'm up for having a look at the suboptimal receivers, at least to see
how hard it would be.  If you
could suggest one that would be useful and point me in the direction
of an appropriate introductory article or
book that would be really helpful.

Cheers,
Ben