[Discuss-gnuradio] Viterbi decoder, wrong decoding

[Michael Höin]

Hi all

I have a problem with the trellis.viterbi block in my receiver. I know
that the transmitter has a convolutional encoder with the generator
polynomials 133,171,145,133. Additionally at the output of the encoder
every 0 bit is converted to a 1 and every 1 is converted to a -1.

With this informations I created the following code:

self.fsm = trellis.fsm(1, 4, [133, 171, 145, 133])
table = [ 1, 1, 1, 1,
          1, 1, 1,-1,
          1, 1,-1, 1,
          1, 1,-1,-1,
          1,-1, 1, 1,
          1,-1, 1,-1,
          1,-1,-1, 1,
          1,-1,-1,-1,
         -1, 1, 1, 1,
         -1, 1, 1,-1,
         -1, 1,-1, 1,
         -1, 1,-1,-1,
         -1,-1, 1, 1,
         -1,-1, 1,-1,
         -1,-1,-1, 1,
         -1,-1,-1,-1]
viterbi_fic = trellis.viterbi_combined_fb(self.fsm, 40, 0, -1, 4, table,
trellis.TRELLIS_EUCLIDEAN)

The problem is that I don't get the right datas out of my viterbi
decoder.
Any idea? Any help will be appreciated.

Thanks,
Michael