[Discuss-gnuradio] gr-trellis : problem in using viterbi decoder

[Raman O]

Hello Achilleas,

I made changes to vector source and sink, encoding works fine with awgn1o2_128.fsm.

But the result of encoder is 2 bit packed and is not suitable for me.
Since i want to employ BPSK modulation (0-> -1 / 1 ->1), I need encoder output 1 bit at a time.

Since awgn1o2_128.fsm dictates  numInputbits: 2 and    numOutputbits: 4 , Modulator throws following error. If i am not wrong it says, constellation length is not enough.

lt-director: gr_chunks_to_symbols_sf.cc:66: virtual int gr_chunks_to_symbols_sf::work(int, gr_vector_const_void_star&, gr_vector_void_star&): Assertion `((unsigned int)in[i]*d_D+d_D) <= d_symbol_table.size()' failed.
Aborted

I am using following Constellation:
 std::vector<float> constellation;
           constellation.push_back(1);
           constellation.push_back(-1);

So how do i achieve BPSK modulation with encoder using generator poly in  awgn1o2_128.fsm.

Many many thanks,
Ram


--- On Mon, 19/7/10, Achilleas Anastasopoulos <address@hidden> wrote:

From: Achilleas Anastasopoulos <address@hidden>
Subject: Re: [Discuss-gnuradio] gr-trellis : problem in using viterbi decoder
To: "Raman O" <address@hidden>, address@hidden
Date: Monday, 19 July, 2010, 9:50 PM

As I mentioned in my earlier email, you have misunderstood the functionality of the

gr_make_vector_source_s(vec,false)

block. It takes a vector "vec" as an argument and produces A STREAM OF SHORTS at its output!!!
It is NOT producing a stream of vectors at its output...unless you specify this as the third parameter,
which has nothing to do with the size of the input vector "vec" you are using...

Please remove both stream2vector and vector2stream from your code and modify the statement

gr_vector_source_s_sptr bit_src = gr_make_vector_source_s(in_bits,false,K );

as

gr_vector_source_s_sptr bit_src = gr_make_vector_source_s(in_bits,false);

Please see the python program test_tcm1.py in the gr-trellis/src/examples directory to see
how the blocks are arranged...

best,
Achilleas

On Mon, Jul 19, 2010 at 4:19 PM, Raman O <address@hidden> wrote:

Hello Achilleas,

 Thanks for your response.
 I have connected encoder block , it disappeared during editing mail by mistake.

Input is in the form of an array of size K and vector2stream feeds encoder bit a time ,so i am using following syntax :

gr_vector_source_s_sptr bit_src = gr_make_vector_source_s(in_bits,false,K );
    
gr_vector_to_stream_sptr vector2stream = gr_make_vector_to_stream(sizeof(short),K)

------------------------------------------------------------------------------------------------------------

int K=100;  
  short inputbits[100]={ ....contains bits....  };
std::vector<short> in_bits;
       
        for (int i = 0; i <K ; i++)  { //  K - no
 of bits
        in_bits.push_back(inputbits[i]); // input bits
        }
        std::vector<float> constellation; // BPSK mapping
          
 constellation.push_back(1);
           constellation.push_back(-1);

    
          
         gr_vector_source_s_sptr bit_src = gr_make_vector_source_s(in_bits,false,K );
  
  
         gr_vector_to_stream_sptr vector2stream= gr_make_vector_to_stream(sizeof(short),K);
    

     // encoder    
           fsm f=
 fsm("../../../gr-trellis/src/examples/fsm_files/awgn1o2_128.fsm");
           trellis_encoder_ss_sptr encoder = trellis_make_encoder_ss (f, 0);
    
     // modulate
 gr_chunks_to_symbols_sf_sptr mod = gr_make_chunks_to_symbols_sf

 (constellation, 1);

     // ----------- ideal channel -------------
    
     // decoder
    
     trellis_metric_type_t type= TRELLIS_EUCLIDEAN;
     trellis_metrics_f_sptr metrics = trellis_make_metrics_f (f.O(), 1,
 constellation, type);

     trellis_viterbi_s_sptr viterbi =trellis_make_viterbi_s ( f,K, 0,-1);
    
     gr_stream_to_vector_sptr stream2vector= gr_make_stream_to_vector(sizeof(short), K);
     d_dst = gr_make_vector_sink_s (K);

          
          connect( bit_src ,   0, vector2stream,   0);

     connect( vector2stream ,   0,encoder, 0);
     connect( encoder ,   0,mod, 0);

     connect(mod,   0,metrics,  

 0);
     connect(metrics,   0, viterbi,   0);
     connect( viterbi,   0,stream2vector,   0);
     connect(stream2vector,   0, d_dst, 0);

 

--- On Mon, 19/7/10, Achilleas Anastasopoulos <address@hidden> wrote:

From: Achilleas Anastasopoulos <address@hidden>
Subject: Re: [Discuss-gnuradio] gr-trellis : problem in using viterbi decoder
To: "gnuradio mailing list" <address@hidden>, address@hidden
Date: Monday, 19 July, 2010, 6:47 PM

I also realized that the way you call
gr_make_vector_source_s(in_bits,false,K );
is incorrect.
I think you have misunderstood what this block does.

You should use:
gr_make_vector_source_s(in_bits,false,1 );
or simply
gr_make_vector_source_s(in_bits,false);
and you really don't need the vector2stream block.

Achilleas



---------------------
In your code the "encoder" block is not connected to any other block...

It should be:

info bits -> encoder -> modulator -> channel -> metrics -> viterbi

Achilleas