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soft output viterbi

Started by S.Diwakar April 19, 2007
Hi,

I very well understand the advantages of soft input being used for viterbi
decoding but, i fail to understand what is the use of soft output?
How is this soft output generated and how is it useful.If its iterative
decoding then we can use this output softbits for further decoding.
please let me know how to generate the soft-output and the use of it.


Rgds,
S.Diwakar.





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On Apr 19, 12:07 pm, "S.Diwakar" <subraveti.diwa...@gmail.com> wrote:
> Hi, > > I very well understand the advantages of soft input being used for viterbi > decoding but, i fail to understand what is the use of soft output? > How is this soft output generated and how is it useful.If its iterative > decoding then we can use this output softbits for further decoding. > please let me know how to generate the soft-output and the use of it. > > Rgds, > S.Diwakar. >
For exactly how to generate soft-output from a Viterbi decoder, search through the archives of this newsgroup or see a coding theory text. You are right in the sense that soft-output is useful only when the next "stage" understands it. Iterative decoding algorithms is one possible use, but there are also serially concatenated codes for which soft-output is useful. Julius
Another example is for instance is the GSM system. Received GMSK symbols
are first equalized using a Viterbi equalizer, which is usually implemented
as a SOVA, such that it can be followed by a soft input Viterbi algorithm
for the actual channel decoding.

Cheers,

Niko