tc-8psk-sect.c

The same two-stage decoder as above. However, when transforming the symbols prior to Viterbi decodin

	  error += (estimate_data2 ^ data_symbol2[indxx % TRUNC_LENGTH]); 

	  if (error)
	    error_count+=error;
	  
#ifdef SHOW_PROGRESS
	  if ( (indxx % DELTA) == 0 )
	    {
        printf("index = %ld\n", indxx);
	      for (i=0; i<TRUNC_LENGTH; i++)
		printf("%x", survivor[0].data[i]);
	      printf("\n--- errors = %ld\n", error_count);
	    }
#endif
	  
	}
      
      printf("%10.5f  %10.4e  %10ld %10ld %4ld\n",
	     snr, ( (double) error_count / ((double) indxx * 2.0) ), 
	     indxx, error_count, NUM_SECT);
      
      fprintf(fp_ber, "%f %20.15f\n", snr,
	      ( (double) error_count / ((double) indxx * 2.0) ));

      fflush(stdout);
      fflush(fp_ber);

      snr += SNR_INC;

    }
  
  fclose(fp_ber);

  return 0;

}



int random_data()
{
  /* 
   * ---------------------------------------------------------------------
   * Random two-bit number generator 
   * ---------------------------------------------------------------------
   */

  return( (random() >> 5) & 3 );
}

void encoder2()
{
  /* 
   * ---------------------------------------------------------------------
   * Conventional convolutional encoder, rate 1/n2 (fixed k_2=1) 
   * ---------------------------------------------------------------------
   */
  register int i, j, result, temp;
  
  temp = memory2;
  output = 0;

 temp = (temp<<1) ^ data_symbol[indxx % TRUNC_LENGTH];

  for (i=0; i<n2; i++)
   {
     result = 0;
     for (j=m2; j>=0; j--)
       result ^= ( ( temp & g2[i][0] ) >> j ) & 1;
     output = ( output<<1 ) ^ result;
   }
  memory2 = temp ;
}


void encoder()
{
  /* 
   * ---------------------------------------------------------------------
   * Conventional convolutional encoder, rate 1/n2 (fixed k_2=1) 
   * ---------------------------------------------------------------------
   */
  register int i, j, result, temp;
  
  temp = memory;
  output2 = 0;

 temp = (temp<<1) ^ survivor[0].data[indxx % TRUNC_LENGTH];

  for (i=0; i<n2; i++)
   {
     result = 0;
     for (j=m2; j>=0; j--)
       result ^= ( ( temp & g2[i][0] ) >> j ) & 1;
     output2 = ( output2<<1 ) ^ result;
   }
  memory = temp ;
}



void transmit()
{
  /* 
   * ---------------------------------------------------------------------
   * Encode and modulate a 1-bit data sequence
   * ---------------------------------------------------------------------
   */
  int i;

  encoder2(); /* */

#ifdef DEB
  printf("memory2 = %x\n", memory2);
#endif

  transmitted = output + 4*data_symbol2[indxx % TRUNC_LENGTH];

}


void re_encode()
{
  /* Re-encode decoded information bit to obtain coset index */

  encoder();
  reconstructed = output2;
}


void awgn()
{
  /* 
   * ---------------------------------------------------------------------
   * Add AWGN to transmitted sequence
   * ---------------------------------------------------------------------
   */
  double u1,u2,s,noise,randmum;
  int i;

#ifdef PRINT
      printf("Received    = ");
#endif

  do
	{	
	  randmum = (double)(random())/MAX_RANDOM;
	  u1 = randmum*2.0 - 1.0;
	  randmum = (double)(random())/MAX_RANDOM;
	  u2 = randmum*2.0 - 1.0;
	  s = u1*u1 + u2*u2;
	} while( s >= 1);

  noise = u1 * sqrt( (-2.0*log(s))/s )/amp;
#ifdef NO_NOISE
  noise = 0.0;
#endif
  received_I = psk_I[transmitted] + noise;

  do
    {
      randmum = (double)(random())/MAX_RANDOM;
      u1 = randmum*2.0 - 1.0;
      randmum = (double)(random())/MAX_RANDOM;
      u2 = randmum*2.0 - 1.0;
      s = u1*u1 + u2*u2;
    } while( s >= 1);

  noise = u1 * sqrt( (-2.0*log(s))/s )/amp;
#ifdef NO_NOISE
  noise = 0.0;
#endif
  received_Q = psk_Q[transmitted] + noise;

#ifdef PRINT
  printf("%4.2lf %4.2lf ", received_I, received_Q);
#endif

#ifdef PRINT
  printf("\n");
#endif

}


void find_sect()
{
  /* ---------------------------------------------------------------------
   * Determine the sector in which the received point lies
   * ---------------------------------------------------------------------
   */

  register int i;
  double ii, phase1, phase2;

  received_angle = atan2(received_Q, received_I);

#ifdef SECTOR
printf("atan2(%lf,%lf)=%lf \t",received_I, received_Q, 
                                               (180.0/3.0)*received_angle);
#endif

  for (i=0; i<NUM_SECT; i++)
    {
      ii = (double) i;
      phase1 = ii*angle_inc;
      if ( phase1 > M_PI )
        phase1 = phase1 - 2.0*M_PI;
      phase2 = (ii+1.0)*angle_inc;
      if ( phase2 > M_PI )
        phase2 = phase2 - 2.0*M_PI;
      if ( (received_angle > phase1) && (received_angle < phase2) )
        sector = i;
    }

#ifdef SECTOR
 printf("--> \tsector = %d\n", sector);
#endif

}



void viterbi()
{
  /* 
   * ---------------------------------------------------------------------
   * Viterbi decoder
   * ---------------------------------------------------------------------
   */

  double aux_metric, surv_metric[NUM_STATES];
  register int i,j,k;

  for (i=0; i<NUM_STATES; i++) /* Initialize survivor branch metric */
    surv_metric[i] = DBL_MAX;

  for (i=0; i<NUM_STATES; i++) /* Loop over inital states */
    {
    for (j=0; j<NUM_TRANS; j++) /* Loop over data */
      {

	  /* Compute metric between received and coded symbols */

      aux_metric = branch_metric[sector][trellis[i][j].output];

	  aux_metric += survivor[i].metric;

#ifdef PRINT
	  printf("rec_I   rec_Q  index_coded\n");
	  printf("%6.2lf %6.2lf %d\n", received_I,received_Q,trellis[i][j].output);
	  printf("init, data, final, metric = %2d %2d %2d %lf\n", i, j,
		 trellis[i][j].final, aux_metric);
#endif

	  /* compare with survivor metric at final state */
      if ( aux_metric < surv_metric[trellis[i][j].final] )

	    { /* Good candidate found */

	      surv_metric[trellis[i][j].final] = aux_metric;

	      /* Update data and state paths */
	      for (k=0; k<TRUNC_LENGTH; k++)
		    {
		      surv_temp[trellis[i][j].final].data[k] =
		        survivor[i].data[k];
		      surv_temp[trellis[i][j].final].state[k] =
		        survivor[i].state[k];
		    }

          surv_temp[trellis[i][j].final].data[indxx%TRUNC_LENGTH] = j;
          surv_temp[trellis[i][j].final].state[indxx%TRUNC_LENGTH] = 
		          trellis[i][j].final;
	    }
      }
    }
  
  for (i=0; i<NUM_STATES; i++)
    {
      /* Update survivor metrics */
      survivor[i].metric = surv_metric[i];

      for (k=0; k<TRUNC_LENGTH; k++)
        {
          survivor[i].data[k] = surv_temp[i].data[k];
          survivor[i].state[k] = surv_temp[i].state[k];
        }
    }
  
#ifdef PRINT
  for (i=0; i<NUM_STATES; i++)
    {
      printf("survivor %2d, initial state = %2d metric = %10.5lf, ", i,
	     survivor[i].state[(indxx-1) % TRUNC_LENGTH], survivor[i].metric);
      printf("\t estimate = %d\n", survivor[i].data[indxx % TRUNC_LENGTH]);
    }
  printf("\n");
#endif

#ifdef DEBUG
  printf("Surviving paths (data):\n");
   for (i=0; i<NUM_STATES; i++)
     {
       printf("%2d --> ",i);
       for (k=0; k<TRUNC_LENGTH; k++)
	 printf("%1x", survivor[i].data[k]);
       printf("\n");
     }
  printf("\n");
#endif

}



void sector_table()
{
  /*
   * ---------------------------------------------------------------------
   * Compute sector metric table:
   * branch_metric[sector][index_ref_signal]
   * ---------------------------------------------------------------------
   */
  register int i,j;
  double ii, ref_I[512], ref_Q[512];
  double phase, metric1, metric2;

  for (i=0; i<NUM_SECT; i++)    /* The sector number is i */
    {
      ii = (double) i;
      phase = (ii+1.0)*angle_inc;
      phase = (ii)*angle_inc;
      ref_I[i] = cos(phase);
      ref_Q[i] = sin(phase);

      for (j=0; j<4; j++)       /* The reference signals are 8-PSK */
        {
          metric1 = ((ref_I[i]-psk_I[j])*(ref_I[i]-psk_I[j]))
                    + ((ref_Q[i]-psk_Q[j])*(ref_Q[i]-psk_Q[j]));
          metric2 = ((ref_I[i]-psk_I[j+4])*(ref_I[i]-psk_I[j+4]))
                    + ((ref_Q[i]-psk_Q[j+4])*(ref_Q[i]-psk_Q[j+4]));
          if (metric1 < metric2)
            branch_metric[i][j] = metric1;
          else
            branch_metric[i][j] = metric2;
        }
    }

#ifdef PRINT_TABLE
printf("--- metric_table --- \n");
  for (i=0; i<NUM_SECT; i++)
  { 
      ii = (double) i;
      phase = (ii+1.0)*angle_inc;

  printf("%7.2lf  |  ", (180.0/M_PI)*phase);
  for (j=0; j<4;j++) printf("%lf  ", branch_metric[i][j]);
  printf("\n");
  }
printf("\n");
#endif

}