convdec.c

wcdma模型

		survivor_metrics[next][new_state] = path_metric;
                set_previous_state(level, new_state, state);
	    }
	  } /* else */

        } /* for over the candidate input symbols */

      } /* for over the encoder states */

#if 1
#ifdef WCDMA_DEBUG_OUTPUT
      for(state=0; state<this->Numb_Encdr_States; state++) {
        if(!state_active[next][state]) continue;
        printf("    at state %d, metric = %f\n",
                      state,survivor_metrics[next][state]);
      }
#endif /* WCDMA_DEBUG_OUTPUT */
#endif

      if (rx_index > this->Decoding_depth-1) {

        /*
         * Produce output from the oldest node in the best path.
         */
        state_on_path = best_path_state;
        for(temp_level=this->Decoding_depth; temp_level>0; temp_level--) {
	    prev_state_on_path = get_prev_state(temp_level, state_on_path);
#ifdef WCDMA_DEBUG_OUTPUT
	    printf("at level %d, path goes thru state %d\n",
					temp_level, prev_state_on_path);
#endif /* WCDMA_DEBUG_OUTPUT */
            last_state = state_on_path;
            state_on_path = prev_state_on_path;
        } /* for */
        decoded_bits[output_index++] = MealyEncoder_GetTransitionTrigger(
						this->Tx_Encoder,
						prev_state_on_path,
						last_state);
#ifdef WCDMA_DEBUG_OUTPUT
        printf("Output: bit %d is %d\n",
                            output_index-1, decoded_bits[output_index-1]);
#endif /* WCDMA_DEBUG_OUTPUT */

      } /* if */

      if (rx_index > this->Decoding_depth-2) {
        /*
         * Remove oldest node from the trellis.
         */
        shift_prev_state_vecs(this->Decoding_depth);
      } /* if */

      /*
       * Switch current and next state information vectors.
       */
      current ^= 0x1;
      next ^= 0x1;

    } /* for over the received symbols */

   return;
} /* wcdma_dec_R1o3_k9_conv */


/* ----------------------------------------------------------- */
/*
 * Function:    wcdma_dec_R1o2_k9_conv
 * Desc.:       Decodes convolutional code (R=1/2, K=9) using
 *              Viterbi algorithm.
 */
void wcdma_dec_R1o2_k9_conv(
	ViterbiDecoder* this,	/* IN: decoder state information */
	int rx_symbols[],	/* IN: vector of received symbols */
	double soft_bits[],	/* IN: vector of soft symbols */
	int rx_size,		/* IN: length of received symbols */
	int tail[],		/* IN: tail bits */
	int tail_size,		/* IN: length of tail */
	int decoded_bits[])	/* OUT: vector of decoded bits */
{
    int state, level, temp_level;
    int inp_symb, tx_symb, rx_symb;
    int new_state;
    unsigned int state_unvisited[256];
    double old_path_metric, branch_metric;
    double path_metric;
    double survivor_metrics[2][256];
    int rx_index, tail_index;
    int info_symb_size;
    double soft_bit;
    double best_path_metric;
    int best_path_state;
    int output_index;
    int current, next;
    unsigned int state_active[2][256];
    int last_state;
    int prev_state_on_path,state_on_path;

    /*
     * Init path metrics and active state tables.
     * If state is active, then we can combine two paths.
     * If state is inactive, then we have't gone through the state.
     */
    for(state=0; state < this->Numb_Encdr_States; state++) {
	survivor_metrics[0][state] = 0;
	survivor_metrics[1][state] = 0;
	state_active[0][state] = FALSE;
	state_active[1][state] = FALSE;
    } 
    state_active[0][0] = TRUE;
    output_index = 0;

    /*
     * Initialize states.
     */
    current = 0;
    next = 1;
    init_prev_state_vecs(this->Decoding_depth);
    
    /*
     * Loop over the received symbols.
     */
    info_symb_size = rx_size + tail_size;
    tail_index = 0;
    for (rx_index=0; rx_index < info_symb_size; rx_index++) {

      /*
       * Init variables.
       */
      for(state=0; state < this->Numb_Encdr_States; state++) {
		state_unvisited[state] = TRUE;
		state_active[next][state] = FALSE;
      }
      best_path_metric = -10000000.0; /* Init to a very big path metric */
      if (rx_index < this->Decoding_depth-1) {
        level = rx_index + 1;
      } else {
        level = this->Decoding_depth-1 + 1;
      }

      /*
       * Get received input symbol. After going through
       * received symbols, fill the shift register with
       * tail symbols.
       */
      if (rx_index < rx_size) {
        rx_symb = rx_symbols[rx_index];
        soft_bit = soft_bits[rx_index];
      } else {
        rx_symb = tail[tail_index++];
        soft_bit = 1.0;
      }
#ifdef WCDMA_DEBUG_OUTPUT
      printf("current rx byte = %d\n",rx_symb);
#endif /* WCDMA_DEBUG_OUTPUT */

      /*
       * Loop over all the encoder states and calculate a path metric
       * for each of them.
       */
      for (state=0; state < this->Numb_Encdr_States; state++) {

        /*
         * If state was not active on the previous level, jump it over.
         */
        if (state_active[current][state] == FALSE) continue;
        /* fprintf(fptr,"  looping state = %d\n",state); */

        /*
         * Loop over all candidate input symbols (0,1).
         */
        for (inp_symb=0; inp_symb < 2; inp_symb++) {

          /*
           * Get the encoder output for this encoder state and input symbol.
           */
	  tx_symb = MealyEncoder_GetOutput(this->Tx_Encoder, state, inp_symb);

          /*
           * Calculate an individual branch metric and a total path metric.
           */
	  branch_metric = MetricTable_R1o2_GetBranchMetric(
			this->Decoding_Metric, rx_symb, soft_bit, tx_symb);
        
	  old_path_metric = survivor_metrics[current][state];
	  path_metric = old_path_metric + branch_metric;
	  new_state = MealyEncoder_GetNextState( this->Tx_Encoder,
							state, inp_symb);

          /*
           * Store the current best candidate.
           */
          if (path_metric > best_path_metric) {
            best_path_metric = path_metric;
            best_path_state = state;
          }

	  /*
	   * If this is the first time we visit this state,
	   * store the branch metrics and previous state.
	   */ 
	  if(state_unvisited[new_state]) {
	    survivor_metrics[next][new_state] = path_metric;
	    state_active[next][new_state] = TRUE;
	    state_unvisited[new_state] = FALSE;
            set_previous_state(level, new_state, state);
	  } else {
	    /*
	     * if the path metric is smaller than the current
	     * store value, replace the current survivor path.
	     */ 
	    if(path_metric > survivor_metrics[next][new_state]) {
		survivor_metrics[next][new_state] = path_metric;
                set_previous_state(level, new_state, state);
	    }
	  } /* else */

        } /* for over the candidate input symbols */

      } /* for over the encoder states */

#if 1
#ifdef WCDMA_DEBUG_OUTPUT
      for(state=0; state<this->Numb_Encdr_States; state++) {
        if(!state_active[next][state]) continue;
        printf("    at state %d, metric = %f\n",
                      state,survivor_metrics[next][state]);
      }
#endif /* WCDMA_DEBUG_OUTPUT */
#endif

      if (rx_index > this->Decoding_depth-1) {

        /*
         * Produce output from the oldest node in the best path.
         */
        state_on_path = best_path_state;
        for(temp_level=this->Decoding_depth; temp_level>0; temp_level--) {
	    prev_state_on_path = get_prev_state(temp_level, state_on_path);
#ifdef WCDMA_DEBUG_OUTPUT
	    printf("at level %d, path goes thru state %d\n",
					temp_level, prev_state_on_path);
#endif /* WCDMA_DEBUG_OUTPUT */
            last_state = state_on_path;
            state_on_path = prev_state_on_path;
        } /* for */
        decoded_bits[output_index++] = MealyEncoder_GetTransitionTrigger(
						this->Tx_Encoder,
						prev_state_on_path,
						last_state);
#ifdef WCDMA_DEBUG_OUTPUT
        printf("Output: bit %d is %d\n",
                            output_index-1, decoded_bits[output_index-1]);
#endif /* WCDMA_DEBUG_OUTPUT */

      } /* if */

      if (rx_index > this->Decoding_depth-2) {
        /*
         * Remove oldest node from the trellis.
         */
        shift_prev_state_vecs(this->Decoding_depth);
      } /* if */

      /*
       * Switch current and next state information vectors.
       */
      current ^= 0x1;
      next ^= 0x1;

    } /* for over the received symbols */

   return;
} /* wcdma_dec_R1o2_k9_conv */


/* ----------------------------------------------------------- */