/*
*******************************************************
ANSI C source code
filename:
	AWGNchannel.c
abstract:
	to support the AWGNchannel
author:
	Shen Ke
version:
	V 1.0
refernce:
	 隨機過程--陳明
********************************************************
*/

#include "QAMSoftDem.h"
#include <math.h>
#include "stdio.h"
#define PI 3.14159



 double random_u(struct AWGN *gauss)
 { 
    double temp;
    gauss->ix = (gauss->ix*249) % 61967; 
    gauss->iy = (gauss->iy*251) % 63443;
    gauss->iz = (gauss->iz*252) % 63599;
    temp= ( (double)gauss->ix/(double)61967 + (double)gauss->iy/(double)63443+ (double)gauss->iz/(double)63599 )
	   -(int)( (double)gauss->ix/(double)61967+ (double)gauss->iy/(double)63443+(double)gauss->iz/(double)63599 );
    return(temp);     
}

 double gauss_g(struct AWGN *gauss)
 {
    double u1,u2;
    double x;
    double var;
    var = gauss->sigma;
    u1=random_u(gauss);
    u2=random_u(gauss);
    x=(double)sqrt((double)(-2)*log((double)1-u1))*(double)cos((double)2*(double)PI*u2);
    x=(double)var*x; /*** 常數系數指標準差 ***/
    return(x);
}


 void awgn_channel (double *in_real ,double *in_img, double *out_real,double*out_img, struct AWGN *gauss , int len)
 {
	int i;
	double add;
	int COLUMN;
	FILE *fpc;

	fpc=fopen("gass.txt","w");
	COLUMN = len;
	for (i=0;i<COLUMN;i++)
	{
	    add = gauss_g(gauss);
	    out_real[i] = in_real[i] + add;
		fprintf(fpc,"%f\n",add);
		add = gauss_g(gauss);
		out_img[i] = in_img[i] + add;
		fprintf(fpc,"%f\n",add);

	}
}