/*
*************************************************************
ANSI C source code
filename:
	16QAMDemodule.c
abstract:
	to perform the 16QAM soft demoduling
author:
	Shen Ke
Version:
	V 1.0
reference:
	the algorithms given by Teacher Huang
*************************************************************
*/

#include "QAMSoftDem.h"
#include "math.h"


#define P1  1/sqrt(10)
#define P3  3/sqrt(10)
#define PM1 -1/sqrt(10)
#define PM3 -3/sqrt(10)

double mincmp (double x,double *sx,int len)
{	
	double minres;
	double tempres;
	int i;
	
	minres = 100.0;
	
	for(i=0;i<len;i++)
	{
		tempres=x-sx[i];
		tempres*=tempres;
		if (minres>tempres) {
			minres = tempres;
		}
		
		
	}
	
	
	
	return minres;
}

/*
***********************************************************
function name:
	LLRfunc
description:
	to perform the function of Log Likelihood Radio	
***********************************************************
*/

int LLRfunc (double x,double *s_1_pos,double *s_0_pos,int len)
{
	double temp1,temp2;
	double compres;
	
	temp1 = mincmp(x,s_0_pos,len);
	temp2 = mincmp(x,s_1_pos,len);
	compres=temp1 - temp2;
	
	if (compres>0) {
		return 1;
	}
	else{
		return 0;
	}
}

/*
***************************************************************
function name:
	QAMdem
description:
	to perform the demoduling
return:
	bitpos
***************************************************************
*/

int QAMDem (double *sig_rel,double *sig_img,int siglen,int *outbit)
{
	int bitpos=0;
	int i;
	int bit0,bit1,bit2,bit3;
	
	
	double sx_1_pos1[2]={PM3,PM1};
	double sx_0_pos1[2]={P3,P1};
	double sx_1_pos3[2]={PM3,P3};
	double sx_0_pos3[2]={PM1,P1};
	double sy_1_pos2[2]={PM3,PM1};
	double sy_0_pos2[2]={P3,P1};
	double sy_1_pos4[2]={PM3,P3};
	double sy_0_pos4[2]={PM1,P1};
	
	for (i=0;i<siglen;i++)
	{
		bit0 = LLRfunc(sig_rel[i],sx_1_pos1,sx_0_pos1,2);
		*(outbit+bitpos)=bit0;
		bitpos++;
		bit1 = LLRfunc(sig_img[i],sy_1_pos2,sy_0_pos2,2);
		*(outbit+bitpos)=bit1;
		bitpos++;
		bit2 = LLRfunc(sig_rel[i],sx_1_pos3,sx_0_pos3,2);
		*(outbit+bitpos)=bit2;
		bitpos++;
		bit3 = LLRfunc(sig_img[i],sy_1_pos4,sy_0_pos4,2);
		*(outbit+bitpos)=bit3;
		bitpos++;
	}
	
	return bitpos;
	
}