RE: [Discuss-gnuradio] How to decode the convolutional code, in the GRC

[intermilan]

Achilleas:
     Do you mean I should put the chunks_to_symbols block between the packet_decoder and Viterbi_combined block? and when I do it , I can get the original data from the viterbi block(I still not add the noise).In my opinion,the function of the chunks_to_symbols block is just to identity the hamming distance. But in the example about TCM (/gnuradio-3.3.0/gr-trellis/src/example),the function of the same block is not just to identity the hamming distance but also some kind of modulator.Am I right about it?

inter

> Date: Mon, 14 Mar 2011 10:11:44 -0400
> From: address@hidden
> To: address@hidden; address@hidden
> Subject: Re: [Discuss-gnuradio] How to decode the convolutional code, in the GRC
>
> inter,
>
> as i said in my previous email, you just have to consider the equivalent
> channel (the fact that it is noiseless is irrelevant in this discussion)
> from the output of the FSM encoder to the input of the VA.
> It seems you prefer to call it equivalent "modulator"; that's fine!
> Once you realize what this equivalent channel/modulator is
> (what is its input/output alphabet and what kind of symbols it
> inputs/outputs) then it will be strainghtforward to see what the viterbi
> decoder block should look like.
> If I were to guess from your description, i would say that your
> equivallent channel
> has input/output alphabet equal to the output alphabet of the FSM.
> Its input is a coded symbol from the FSM encoder and its output is also
> such a symbol from the packet decoder.
> So all you need is to do VA with symbol-wise hamming distance as your
> metric. You can achieve that using the viterbi_combined block with
> a trivial 1-D chunks to symbols block (identity) and the appropriate
> parameter for the metric_type.
>
>
> Achilleas
>
> On 3/14/2011 6:45 AM, intermilan wrote:
> > Achilleas:
> >
> > What I want to do is want to see the BER when the convolutional code is
> > used in different modulator in the GRC,but I had not put the noise
> > source in the flow graph so there is no noise between the modulator and
> > demodulator.
> > Besides,in my opinion, we can consider the packet_encoder and
> > packet_decoder block is part of the modulation.In other words,in the
> > flow graph I mentioned ,the data input the packet_encoder is the same as
> > the packet_decoder block(because I did not put the noise block between
> > the modulator and demodulator ).
> > But I still not understand how to set the parameters in the viterbi
> > block in this case, particularly the parameter constellation if I do not
> > use the chunks_to_symbols block.
> > Thanks for your help.
> >
> > inter
> >
> > > Date: Fri, 11 Mar 2011 17:33:25 -0500
> > > From: address@hidden
> > > To: address@hidden; di! address@hidden
> > > Subject: RE: [Discuss-gnuradio] How to decode the convolutional code,
> > in the GRC
> > >
> > >
> > > inter,
> > >
> > > think of whatever is AFTER the trellis encoder and BEFORE the viterbi
> > > decoder as an equivalent channel.
> > >
> > > What is the equivalent channel in your case?
> > > What is its input alphabet? what is its output alphabet?
> > >
> > > From your description, it seems that the input alphabet is the same as
> > > the output alphabet of your FSM.
> > >
> > > I am not familiar with the block "packet decoder" so i don't know what
> > > it outputs, but whatever it is it should be the output alphabet of your
> > > "equivalent" channel.
> > >
> > > Once you figure out these things it will be straightforward to see what
> > > the viterbi block should be...
> > > If you gather these pieces of information and still don't see how to
> > > implement the viterbi decoder let me know ! and i will provide
> > further help.
> > >
> > > Achilleas
>
> --
> _______________________________________________________
> Achilleas Anastasopoulos
> Associate Professor
> EECS Department Voice : (734)615-4024
> UNIVERSITY OF MICHIGAN Fax : (734)763-8041
> Ann Arbor, MI 48109-2122 E-mail: address@hidden
> URL: http://www.eecs.umich.edu/~anastas/
> _______________________________________________________