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/* file: ViterbiDecode.c
Description: Soft-in/hard-out decoding for a convolutional code using the Viterbi algorithm
The calling syntax is:
[output_u] = ViterbiDecode( input_c, g_encoder, [code_type], [depth] )
output_u = hard decisions on the data bits (0 or 1)
Required inputs:
input_c = LLR of the code bits (based on channel observations)
g_encoder = generator matrix for convolutional code
(If RSC, then feedback polynomial is first)
Optional inputs:
code_type = 0 for recursive systematic convolutional (RSC) code (default)
= 1 for non-systematic convolutional (NSC) code
= 2 for tail-biting NSC code
depth = wrap depth used for tail-biting decoding
default is 6 times the constraint length
Copyright (C) 2005-2008, Matthew C. Valenti
Last updated on May 21, 2008
Function ViterbiDecode 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>
/* library of functions */
#include "./include/convolutional.h"
/* Input Arguments */
#define INPUT_C prhs[0]
#define GENENCODER prhs[1]
#define CODETYPE prhs[2]
#define DEPTH prhs[3]
/* Output Arguments */
#define OUTPUT_U plhs[0]
/* main function that interfaces with MATLAB */
void mexFunction(
int nlhs,
mxArray *plhs[],
int nrhs,
const mxArray *prhs[] )
{
double *input_c, *g_array; /* input arrays */
double *output_u_p; /* output arrays */
int DataLength, CodeLength, i, j, index, depth;
mwIndex subs[] = {1,1};
int *g_encoder;
int nn, KK, mm, max_states, code_type;
double elm;
float *input_c_float;
int *output_u_int;
int *out0, *out1, *state0, *state1;
/* Check for proper number of arguments */
if (nrhs < 2 ) {
mexErrMsgTxt("Usage: [output_u] = ViterbiDecode( input_c, g_encoder, [code_type], [depth] )");
} else {
/* first input is the LLRs of the code bits */
input_c = mxGetPr(INPUT_C);
/* second input specifies the code */
g_array = mxGetPr(GENENCODER);
nn = mxGetM(GENENCODER);
KK = mxGetN(GENENCODER);
mm = KK - 1;
max_states = 1 << mm; /* 2^mm */
CodeLength = mxGetN(INPUT_C); /* number of code bits */
/* Make sure CodeLength is a multiple of nn */
if ( CodeLength % nn > 0)
mexErrMsgTxt("Length of input_c must be a multiple of n, the number of rows in g");
/* default values */
code_type = 0;
/* 3rd input (optional) is the type of code */
if (nrhs > 2 ) {
code_type = (int) *mxGetPr(CODETYPE);
}
/* determine the DataLength */
if ( code_type < 2 ) {
DataLength = (CodeLength/nn)-mm;
} else {
DataLength = CodeLength/nn;
/* 4th input (optional) is the wrap depth */
if (nrhs > 3) {
depth = (int) *mxGetPr(DEPTH);
depth = depth*KK;
} else {
depth = 6*KK;
}
}
/* convert the input into float */
input_c_float = (float*)calloc( CodeLength, sizeof(float) );
for (i=0;i<CodeLength;i++)
input_c_float[i] = input_c[i];
/* Convert code polynomial to binary */
g_encoder = (int*)calloc(nn, sizeof(int) );
for (i = 0;i<nn;i++) {
subs[0] = i;
for (j=0;j<KK;j++) {
subs[1] = j;
index = mxCalcSingleSubscript(GENENCODER, 2, subs);
elm = g_array[index];
if (elm != 0) {
g_encoder[i] = g_encoder[i] + (int) pow(2,(KK-j-1));
}
}
/* mexPrintf(" g_encoder[%d] = %o\n", i, g_encoder[i] ); */
}
}
if (nlhs > 1) {
mexErrMsgTxt("Usage: [output_u] = ViterbiDecode( input_c, g_encoder, [code_type], [depth] )" );
}
/* the outputs */
OUTPUT_U = mxCreateDoubleMatrix(1, DataLength, mxREAL );
output_u_p = mxGetPr(OUTPUT_U);
output_u_int = (int*)calloc( DataLength, sizeof(int) );
/* create appropriate transition matrices */
out0 = (int*)calloc( max_states, sizeof(int) );
out1 = (int*)calloc( max_states, sizeof(int) );
state0 = (int*)calloc( max_states, sizeof(int) );
state1 = (int*)calloc( max_states, sizeof(int) );
if ( code_type ) {
nsc_transit( out0, state0, 0, g_encoder, KK, nn );
nsc_transit( out1, state1, 1, g_encoder, KK, nn );
} else {
rsc_transit( out0, state0, 0, g_encoder, KK, nn );
rsc_transit( out1, state1, 1, g_encoder, KK, nn );
}
/* Run the Viterbi algorithm */
if ( code_type < 2 ) {
Viterbi( output_u_int, out0, state0, out1, state1,
input_c_float, KK, nn, DataLength );
} else {
ViterbiTb( output_u_int, out0, state0, out1, state1,
input_c_float, KK, nn, DataLength, depth );
}
/* cast to outputs */
for (j=0;j<DataLength;j++) {
output_u_p[j] = output_u_int[j];
}
/* Clean up memory */
free( out0 );
free( out1 );
free( state0 );
free( state1 );
free( g_encoder );
free( input_c_float );
free( output_u_int );
return;
}
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