Forum: GNU Radio Re: Problem in using trellis Error, correction en- and decoder

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Francisco Llaryora (Guest)
on 2010-11-06 00:40
(Received via mailing list)
in the past Achilleas wrote:-------
There are a couple of potential problems with your flowgraph:

1) the trellis encoder outputs unpacked bytes. For example, if your FSM
output cardinality 4 then it outputs 2 useful bits per byte.

Are you sure you are handling this the right way at the packet encoder?
I do not know how that block works but you should check it.

however, the main problem is the following

2) You need to substitute the "trellis viterbi" by the "trellis viterbi
block and input as parameters the kind of "distance" metric you want and
corresponding constellation, etc. To do that you need to know what is
output of the packet decoder...

I have never worked with packet en/decoder so i cannot help with these.

-------------end of quote.

well, I first want to thank you, because it success. (The problem is
I did simplify the example: a source, a trellis and a viterbi combo.
Next, change the types for bytes.
Next use 'packed to unpacked' in the head.and 'unpacked to packed' in
tail of the flow.

i test with noise source the trellis, trellis-D8psk and trellis-DBPSK.
 trellis-DBPSK in noise is better than trellis in noise .
but  trellis in noise  is better than  trellis-D8psk in noise.

DBPSK Hamming distance=2.
trellis Hamming distance=sqrt(2).
D8pskHamming distance<sqrt(2).

the snapshot...where are the snapshot?

3297f492e9d0f62696428b52277d0b29?d=identicon&s=25 sivakumar r. (sivakumar_r)
on 2014-04-28 08:16
(Received via mailing list)
Could you please let me know, how to set FSM args value in Trellis
coder. I am
also using trellis coder for my work Please reply ASAP.
Ron Economos (Guest)
on 2014-04-28 09:12
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I'm not exactly an expert on this, but correct values
for the DVB-S trellis encoder (1/2 rate, G1(X) = 121,
G2(Y) = 91) are:

1, 2, (121, 91)

My DVB-S transmitter repository is here:

Johannes Demel (Guest)
on 2014-04-28 14:55
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Hey Siva,

in [1] I parameterized the trellis module for a rate 1/3 code as used in
LTE. Maybe that helps. I put a lot of comments in.
Besides if you tell us what you want to achieve exactly, someone might
give more specific hints.

happy hacking

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