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

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,
>>      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