softdemodulator.c

根据LDPC码中码子的构造方法中的PEG算法

#define _1_DIV_SQRT_2PI 0.398942280
//#define EPS 1e-10

#include <math.h>
#include <iostream.h>
#include "SoftDemodulator.h"
#include "Constant.h"

SoftDemodulator::SoftDemodulator(double sigma, int isiSize) {
  (*this).sigma = sigma;
  factor1 = 1.0/sigma;
  factor2 = factor1*factor1/2.0;
  (*this).isiSize=isiSize;
  isiAlphabet=new int [2];
  isiAlphabet[0]=-1;
  isiAlphabet[1]=1;
}

SoftDemodulator::~SoftDemodulator() {
  delete [] isiAlphabet;
}

void SoftDemodulator::getProbabilities(const double *y, int length, double *(*prob)) {
#ifdef SOFTDEMODULATOR_DEBUG
  cout << "CHANNEL TRANSITION PROBABILITIES:\n";
#endif
  for (int i = 0; i < length; i++) {
    for (int j = 0; j < isiSize; j++) {
      double diff = y[i] - isiAlphabet[j];
      prob[i][j] = _1_DIV_SQRT_2PI*factor1*exp(-(diff*diff)*factor2);
      if (prob[i][j] < EPS) {
	prob[i][j] = EPS;
      }

#ifdef SOFTDEMODULATOR_DEBUG
      cout << prob[i][j] << "          ";
#endif

    }

#ifdef SOFTDEMODULATOR_DEBUG
    cout << "\n";
#endif

  }
#ifdef SOFTDEMODULATOR_DEBUG
  cout << "\n";
#endif

}

void SoftDemodulator::setSigma(double sigma) {
  (*this).sigma = sigma;
  factor1 = 1.0/sigma;
  factor2 = factor1*factor1/2.0;
}