Re: [Discuss-gnuradio] Gr-trellis ; convolutional code and, convolutionnal interleaver.

[Achilleas Anastasopoulos]

Axel,

regarding your interleaver question:
Block or convolutional, I suspect that any practical application will 
use a convolutional interleaver in a "block" fashion, ie
it will have M symbols in the input and produce M symbols at the output 
where the positions are permuted.
If you can describe this permutation, and put it in a file then
you can use the gr-trellis version of interleaver.
For instance a length 5 interleaver looks like that:
3 1 5 4 2
which means that the first symbol goes to position 3, the second to 
position 1 the third to position 5, etc. I have included at least one 
exampl in the examples directory og gr-trellis.

If this is not the case and you still want a semi-infinite sequence as 
the input you can easily write your own block for the convolutional 
interleaver; it seems pretty straightforward as it consists of a 
demultiplexer 1-to-N, multiple delay elements with different delays
D(1), D(2),...,D(N), and an N-to-1 multiplexer. Hey, this can even be 
done as a hierarchical block using existing gnuradio blocks...

Achilleas

Axel Belliard wrote:
> Hi
> Thanks for answering my questions.
>
> I changed my code, it works now.
> I will try the random interleaver, to see how it works. But in the end I
> will need a super control over it. I need something that look like that :
> http://www.mathworks.com/access/helpdesk/help/toolbox/commblks/ug/fp60504.html
> (see convolutional interleaver section).
>
> Thanks again
>
> Axel
>
> On Tue, April 13, 2010 7:58 pm, Achilleas Anastasopoulos wrote:
> > Axel,
> >
> >
> >
> > First, there is no such thing in gr-trellis as a "convolutional
> > interleaver". There is only a generic interleaver, ie a permutation which
> > is defined through the different constructors provided in interleaver.h
> > (through a file, random, etc).
> > If you do not want to have super control over it i suggest you start
> > with just a random interleaver and see how it works.
> >
> > Second, I see a minor problem in your code:
> > the viterbi block should specify the block size as its 2nd parameter so
> > instead of
> >
> > self.va = trellis.viterbi_s(f,2,0,-1)
> >
> > you should put something like
> >
> > self.va = trellis.viterbi_s(f,len(self.src_data),0,-1)
> >
> > I tried this modification and works fine with me.
> > Let me know if you have any problems,
> > Achilleas

--
_______________________________________________________
Achilleas Anastasopoulos                        
Associate Professor
EECS Department               Voice : (734)615-4024
UNIVERSITY OF MICHIGAN        Fax   : (734)763-8041
Ann Arbor, MI 48109-2122      E-mail: address@hidden
URL: http://www.eecs.umich.edu/~anastas/        
_______________________________________________________