Re: [Discuss-gnuradio] gr-fec Viterbi example

[Gisle Vanem]

Jean-Michel FRIEDT wrote:

> I am currently investigating LRPT (as used by METEOR-M2) and am
> stuck with the Viterbi decoder. While trying to use
> https://github.com/gnuradio/gnuradio/blob/master/gr-fec/lib/viterbi/decode.cc
> which implements

I tried building this program on Windows and failed. Since it's
missing in viterbi/CmakeLists.txt, I fail to see it's built by
default. How did you compile it? Are you sure it wasn't written
on a big-endian machine?

On Windows at least, the viterbi.h + decode.cc + encode.cc are
not up-to-date. Missing proper dllexport, setmode(fd,O_BINARY)
etc. etc.

Anyway, with some patching I was able to link and run them.
But I have no data to test the Viterbi encoder/decoder with.
Could you please ship some files to me?

> I am unable to encode the sync word 0x1ACFFC1D to the expected result
> 0xfc 0xa2 0xb6 0x3d 0xb0 0x0d 0x97 0x94 as explained at
> https://www.teske.net.br/lucas/2016/11/goes-satellite-hunt-part-3-frame-decoder/
> I know this encoded sync word is correct because cross-correlating the
> METEOR stream (after proper constellation rotation) with this word gives
> a correlation peak every 16384 samples (=1024 byte sentence * 8 bits/byte * 2
> bits/Viterbi encoder).
>
> I am doing (word.bin was generated with Octave's fwrite function)
> $ xxd word.bin
> 00000000: 1acf fc1d 0000 0000 0000                 ..........
> and then
> $ cat word.bin | ./viterbi/encode > t.bin
> but
> $ xxd t.bin
> 00000000: 0000 0000 0000 0101 0001 0001 0101 0001  ................
> 00000010: 0001 0000 0100 0001 0101 0000 0000 0100  ................
> 00000020: 0001 0000 0101 0101 0101 0101 0000 0100  ................
> 00000030: 0001 0100 0100 0000 0001 0100 0100 0101  ................
> 00000040: 0000 0001 0001 0101 0001 0101 0000 0000  ................
> does not match the expected bit sequence which should be
> word=[1 1 1 1 1 1 0 0 ... %  fc
>        1 0 1 0 0 0 1 0 ... %  a2
>        1 0 1 1 0 1 1 0 ... %  b6
>        0 0 1 1 1 1 0 1 ... %  3d
>        1 0 1 1 0 0 0 0 ... %  b0
>        0 0 0 0 1 1 0 1 ... %  0d
>        1 0 0 1 0 1 1 1 ... %  97
>        1 0 0 1 0 1 0 0 ... %  94

I had no lock with 'xxd -revert' to check your results here
I used the attached hex2bin.c instead.

And BTW, my patches also attached.

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--gv

hex2bin.c
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gr-fec.diff
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