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 colby.bo...@gmail.com:
> 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,
>> Jonas
>>
>
> 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
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