|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: t=trellis.fsm(1,2,[91,121]) 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... Regards, Jonas 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 = trellis.viterbi_combined_fb(fo,nsymbols,0,-1,1,[-1,1],trellis.TRELLIS_EUCLIDEAN) 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. Regards, JonasIf 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.
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