[Top][All Lists]

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

[Discuss-gnuradio] Re: gr-trellis: convenc and viterbi with own mapper/d

From: colby . boyer
Subject: [Discuss-gnuradio] Re: gr-trellis: convenc and viterbi with own mapper/de-mapper
Date: Mon, 16 Aug 2010 23:30:48 -0700 (PDT)
User-agent: Alpine 2.00 (DEB 1167 2008-08-23)

On Tue, 17 Aug 2010, "Jonas M. Börner" wrote:

Hi Colby,

thanks for your reply. My trellis is created like this:


The constraint length is 7 so it doesn't look like it was connected to a 
trellis-specific thing. As I remember from the gr-trellis examples they didn't 
do any truncating there before comparing the source with the destination for 
error calculation...


Am 17.08.2010 um 08:10 schrieb address@hidden:

On Mon, 16 Aug 2010, Jonas M. Börner wrote:

Hi all,

I am trying to use the convolutional encoder and Viterbi provided by the 
gr-trellis class within another environment. I have my own mapper and de-mapper 
blocks which I want to use. So I tried to use the feed the viterbi_combined 
with this arguments:

va_combined = 

My de-mapper outputs soft bits between -1 and +1. Here is an example output of 
my test script:

data:           [0, 1, 1, 0, 0]
encoded:        (0, 3, 2, 2, 0)
unpacked:       (0, 0, 1, 1, 1, 0, 1, 0, 0, 0)
modulated:      ((1+0j), (1+0j), (-1+0j), (-1+0j), (-1+0j), (1+0j), (-1+0j), 
(1+0j), (1+0j), (1+0j))
demodulated:    (-1.0, -1.0, 1.0, 1.0, 1.0, -1.0, 1.0, -1.0, -1.0, -1.0)
decoded:        (0, 0, 1, 0, 0, 1, 0, 1, 0, 1)

Another thing I don't understand is why the decoder outputs 10 values instead 
of 5. I would be glad if someone told me what I am doing wrong.


If I remember correctly, when you start pushing symbols through the trellis, it 
has some zero values before the input and some zero values after your last 
symbol pushed into the trellis. I think this is typically the length of your 
trellis. So at some point you will have to truncate the trellis output.

Any one else care to comment?

--Colby Boyer

I have not used the GNU Radio trellis before. In the past, I have only used the the matlab trellis and I remember I had to deal with truncating.


reply via email to

[Prev in Thread] Current Thread [Next in Thread]