convencoder.c

卷积码的编码及解码代码

/* MATLAB's C-MEX convolutional code encoder
 *
 * Copyright Bagawan S. Nugroho, 2006 
 *********************************************/

#include "mex.h"
#include <stdlib.h>

void shiftReg( short *out, double *g, double *x, int inLen, int ioR, short R, short K)
/* Convolve the input and tail vector according to generator matrix g */

{   
   short NN;
   int i, j;
   div_t N;
   
   /* Number of state's bits = constraint lengths K */
   short state[9] = {0,0,0,0,0,0,0,0,0};
   
   /* Convolve the input bits */
   for( i = 0; i < inLen; i++) {
      NN = 0;
      /* Data in */
      *state = *(x + i);
      for( j = 0; j < K; j++) {
         N = div( (NN + *(state + j)**(g + j*R + ioR)), 2);
         NN = N.rem;
      } /* for j */
      
      /* Update the output vector */
      *(out + i*R + ioR) = NN;
      
      /* Update state */
      for( j = K - 1; j > 0; j--) {
         *(state + j) = *(state + j - 1);         
      } /* for j */
   } /* for i */
      
   /* Convolve the zero bits tail */
   for( i = inLen; i < inLen + K - 1; i++) {
      NN = 0;
      /* Zeros tail */
      *state = 0;
      for( j = 0; j < K; j++) {
         N = div( (NN + *(state + j)**(g + j*R + ioR)), 2);
         NN = N.rem;
      } /* for j */
      
      /* Update the output vector */
      *(out + i*R + ioR) = NN;
      
      /* Update state */
      for( j = K - 1; j > 0; j--) {
         *(state + j) = *(state + j - 1);         
      } /* for j */
   } /* for i */   
}

/* ----------- The main function ----------- */
void convEncoder( double *x, double *y, double *G, int inLen, short R, short K)
/* x, input vector
 * G, generator matrix
 * inLen, data length
 * R, code rate (1/R)
 * K, constraint length
 *
 * y, output vector. */

{
   short out[10240];
   int i;   
   
   for( i = 0; i < R; i++) {     
      shiftReg( out, G, x, inLen, i, R, K); 
   } /* for i */
   
   /* Return the vector's result to the gateway output */
   for( i = 0; i < R*(inLen + K - 1); i++) {
      *(y + i) = (double) *(out + i);
   } /* for i */   
}

/* ---------- The gateway function ---------- */
void mexFunction( int nlhs, mxArray *plhs[],
                    int nrhs, const mxArray *prhs[] )

/* input: G = prhs[0], generator matrix
 *        x = prhs[1], input vector (1/0)
 *     
 *
 * output: y = plhs[0], output vector (0/1). */
{    
   double *x, *y, *G;
   short row, col;
   int inLen;
        
   /* Create pointer to the input matrix G */
   G = mxGetPr( prhs[0]);
   
   /* Create pointer to the input vector x */
   x = mxGetPr( prhs[1]);
       
   /* Get the dimensions of the matrix generator G */
   row = mxGetM( prhs[0]);
   col = mxGetN( prhs[0]);   
   
   /* Get the length of the vector input x */
   inLen = mxGetN( prhs[1]);
         
   /* Set the output pointer to the output vector */   
   plhs[0] = mxCreateDoubleMatrix( 1, row*(inLen + col - 1), mxREAL);
    
   /* Create a pointer to a copy ot the output vector y */
   y = mxGetPr( plhs[0]);
    
   /* Call the main subroutine */
   convEncoder( x, y, G, inLen, row, col);            
}