Re: [Discuss-gnuradio] Convolutional Code output does not match polynomial

[bob wole]

I have opened an issue on the gnuradio.org. See the link below

http://gnuradio.org/redmine/issues/841


--

Bob

On Sat, Sep 12, 2015 at 1:36 PM, bob wole <address@hidden> wrote:

Okay. I registered my self at gnuradio.org. Do I have to open a new Issue on the website?

--

Bob

 

Jan, Bob,

might be worth opening a ticket for this.

M
On 10.09.2015 00:22, bob wole wrote:
> Hey Jan,
>
> Thanks for your reply, you are correct about the bit shift being LSB.
> So, I reversed the bit order of polynomials 1101101 to 1011011 and
> 1001111 to 1111001 in MATLAB, Now the output of gnuradio and MATLAB and
> my dry run matches. I am wondering why they did implementation like
> this? Any advantages?
>
> Yeah, I too was hoping for a reply from Tom and Nick on this.
>
>
> --
> Bob
>
>
> On Tue, Sep 8, 2015 at 12:37 PM, Jan Kr?mer <address@hidden
> <mailto:address@hidden>> wrote:
>
>     Also I think Tom and Nick Foster for sure know more about it than I do.
>
>     Cheers,
>     Jan
>
>     2015-09-08 8:44 GMT+02:00 Jan Kr?mer <address@hidden
>     <mailto:address@hidden>>:
>
>         Hey Bob,
>
>         I have the same issues with my SSE Viterbi, works with
>         gr-trellis but not with cc_encoder in gr-fec. The output of the
>         cc_encoder is legit though.
>         I talked to a couple of guys about this at last year's GRCON. It
>         seems that in most implementations, the bit order of the
>         polynomials is reversed when compared to the textbook approach.
>         Therefor also the bit shifting in the encoding process (and the
>         viterbi chainback) is also reversed. I think textbook is MSB
>         while cc_encoder is LSB but I always mix them up xD.
>         But you can check
>         https://github.com/gnuradio/gnuradio/blob/master/gr-fec/lib/cc_encoder_impl.cc
>         beginning from line 166.
>
>         Hope that helps,
>         Jan
>
>         2015-09-08 8:12 GMT+02:00 bob wole <address@hidden
>         <mailto:address@hidden>>:
>
>
>
>             On Tue, Sep 1, 2015 at 2:55 PM, bob wole <address@hidden

>             <mailto:address@hidden>> wrote:
>
>                 I am trying channel coding in gnuradio. I am using
>                 convolutional encoder with K=7 and R=1/2 with
>                 polynomials [109, 79] (default). However I am not
>                 getting the expected result. I input a known bit
>                 sequence, single frame using head block, and observe the
>                 output of the encoder using file sink. The output I
>                 think is not correct according to the given polynomials.
>                 Input bit stream is
>
>                 http://pastebin.com/thsYtLFG
>
>                 I am getting this output
>
>                 http://pastebin.com/P42QNjiE
>
>                 However, I am expecting (in hex)
>
>                 00    00    E3    32    63    D7    4B    FA    D3 ......
>
>
>                  I have attached the flowgraph I am using for this
>                 purpose. I did a dry run by drawing a diagram of the
>                 encoder and inputing  initial two bytes. Diagram of the
>                 encoder is also attached. I also used MATLAB script to
>                 test and found that my dry run output matches with
>                 MATLAB but not with Gnuradio output. I also played with
>                 the endianness but could not get the desired result.
>                 Maybe I am doing something wrong in configuring the encoder?
>
>
>                 Also another thing I noticed is that in QA codes of
>                 gr-fec I found
>
>                 import fec_swig as fec
>                 import blocks_swig as blocks
>
>                 I think this should be
>
>                 from gnuradio import fec, blocks
>
>                 Am I right? I am using gnuradio 3.7.8.
>
>                 --
>                 Bob
>
>
>
>             I am still waiting to get a reply on this. Anyone else
>             verified the output of the convolutional encoder?
>
>
>             --
>             Bob