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/* File: Demod2D.c
Description: Transforms received symbols into ML symbol log-likelihoods
The calling syntax is:
[output] = Demod2D( input, S_matrix, EsNo, [fade_coef] )
Where:
output = M by N matrix of symbol log-likelihoods
input = 1 by N matrix of (complex) matched filter outputs
S_matrix = Length M complex vector representing the constellation
EsNo = the symbol SNR (in linear, not dB, units)
fade_coef = 1 by N matrix of (complex) fading coefficients (defaults to all-ones)
Copyright (C) 2005-2006, Matthew C. Valenti
Last updated on May 6, 2006
Function Demod2D is part of the Iterative Solutions
Coded Modulation Library. The Iterative Solutions Coded Modulation
Library is free software; you can redistribute it and/or modify it
under the terms of the GNU Lesser General Public License as published
by the Free Software Foundation; either version 2.1 of the License,
or (at your option) any later version.
This library is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public
License along with this library; if not, write to the Free Software
Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
*/
#include <math.h>
#include <mex.h>
#include <Matrix.h>
#include <stdlib.h>
/* Input Arguments
prhs[0] is input
prhs[1] is S_matrix
prhs[2] is EsNo
prhs[3] is fade_coef */
/* Output Arguments
plhs[0] is output */
/* main function that interfaces with MATLAB */
void mexFunction(
int nlhs,
mxArray *plhs[],
int nrhs,
const mxArray *prhs[] )
{
int M;
int number_symbols;
float EsNo;
double *Sr, *Si , *ar, *ai, *yr, *yi, *output;
int i,j;
double tempsr, tempsi, Er, Ei;
/* make sure there are enough inputs */
if (nrhs<3)
mexErrMsgTxt("Usage: [output] = Demod2D( input, S_matrix, EsNo, [fade_coef] )");
/* read in the inputs */
number_symbols = mxGetN(prhs[0]);
yr = mxGetPr(prhs[0]);
if(!mxIsComplex(prhs[0]) )
yi = (double*)calloc( number_symbols, sizeof(double) );
else
yi = mxGetPi(prhs[0]);
if (mxGetN(prhs[1])==1) /* column vector */
M = mxGetM( prhs[1] );
else if (mxGetM(prhs[1])==1) /* row vector */
M = mxGetN( prhs[1] );
else
mexErrMsgTxt("S_matrix should only have one column or row");
Sr = mxGetPr(prhs[1]);
if (!mxIsComplex(prhs[1]) )
Si = (double*)calloc( M, sizeof(double) );
else
Si = mxGetPi(prhs[1]);
EsNo = (float) *mxGetPr(prhs[2]);
if(nrhs>3) {
if (mxGetN(prhs[3])!=number_symbols)
mexErrMsgTxt("Fading process must be same length as received signal");
ar = mxGetPr(prhs[3]);
if (!mxIsComplex(prhs[3]) )
ai = (double*)calloc( number_symbols, sizeof(double) );
else
ai = mxGetPi(prhs[3]);
} else {
ar = (double*)calloc( number_symbols, sizeof(double) );
for (i=0;i<number_symbols;i++)
ar[i] = 1; /* assume AWGN if no fading process specified */
ai = (double*)calloc( number_symbols, sizeof(double) );
}
plhs[0]=mxCreateDoubleMatrix(M, number_symbols, mxREAL);
output = mxGetPr( plhs[0] );
/* determine output */
for (i=0;i<number_symbols;i++) { /* go through each received symbol */
for (j=0;j<M;j++) { /* each postulated symbol */
tempsr = ar[i]*Sr[j]-ai[i]*Si[j];
tempsi = ai[i]*Sr[j]+ar[i]*Si[j];
Er = yr[i]-tempsr;
Ei = yi[i]-tempsi;
output[i*M+j] = -EsNo*(Er*Er+Ei*Ei);
}
}
/* free memory */
if(!mxIsComplex(prhs[0]) )
free(yi);
if(!mxIsComplex(prhs[1]) )
free(Si);
if (nrhs>3) {
if(!mxIsComplex(prhs[3]) )
free(ai);
} else {
free(ar);
free(ai);
}
}
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