# Re: Problem in using trellis Error, correction en- and decoder

**URL:** <https://www.ruby-forum.com/t/re-problem-in-using-trellis-error-correction-en-and-decoder/198715>\
**Category:** GNU Radio\
**Created:** [November 6, 2010, 12:40am UTC](https://www.ruby-forum.com/t/re-problem-in-using-trellis-error-correction-en-and-decoder/198715 "2010-11-06T00:40:46Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![okkezSS](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/o/85f322/32.png) [@okkezSS](https://www.ruby-forum.com/u/okkezSS)\
**Post date:** [November 6, 2010, 12:40am UTC](https://www.ruby-forum.com/t/re-problem-in-using-trellis-error-correction-en-and-decoder/198715/1 "2010-11-06T00:40:46Z")

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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  
has  
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

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

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

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

well, I first want to thank you, because it success. (The problem is  
solved).  
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  
the  
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?  
[http://img808.imageshack.us/img808/1725/pantallazointerferencec.png](http://img808.imageshack.us/img808/1725/pantallazointerferencec.png)

bye.

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**Author:** ![Francisco\_Llaryora](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/f/ac8455/32.png) [@Francisco\_Llaryora](https://www.ruby-forum.com/u/Francisco_Llaryora)\
**Post date:** [April 28, 2014, 8:16am UTC](https://www.ruby-forum.com/t/re-problem-in-using-trellis-error-correction-en-and-decoder/198715/2 "2014-04-28T08:16:42Z")

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Dear,  
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.

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**Author:** ![Francisco\_Llaryora](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/f/ac8455/32.png) [@Francisco\_Llaryora](https://www.ruby-forum.com/u/Francisco_Llaryora)\
**Post date:** [April 28, 2014, 9:12am UTC](https://www.ruby-forum.com/t/re-problem-in-using-trellis-error-correction-en-and-decoder/198715/3 "2014-04-28T09:12:17Z")

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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:

> **[GitHub - drmpeg/gr-dvbs: A DVB-S transmitter for GNU Radio](https://github.com/drmpeg/gr-dvbs)**
>
> A DVB-S transmitter for GNU Radio. Contribute to drmpeg/gr-dvbs development by creating an account on GitHub.

Ron

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**Author:** ![Francisco\_Llaryora](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/f/ac8455/32.png) [@Francisco\_Llaryora](https://www.ruby-forum.com/u/Francisco_Llaryora)\
**Post date:** [April 28, 2014, 2:55pm UTC](https://www.ruby-forum.com/t/re-problem-in-using-trellis-error-correction-en-and-decoder/198715/4 "2014-04-28T14:55:16Z")

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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  
Johannes

[1]

> <https://github.com/kit-cel/gr-lte/blob/master/python/bch_viterbi_vfvb.py>