cyclint.c

error correction code

// ------------------------------------------------------------------------
// File: cyclint.c
// Date: April 5, 2002
// Description: Generate a CYCLIC interleaver. The output is an interleaver
// array in a file with name specified at command input line.
//
// NOTE: This is equivalent to a Ramsey/convolutional interleaver with
//       delay D. (See text, p. 116)
//
// Example: N1=3 N2=5 D=2
//
//                   0   3   6   9  12 
//                   1   4   7  10  13 
//                   2   5   8  11  14 
//
// Delay:
//                   0   3   6   9  12 
//                  10  13   1   4   7 
//                   5   8  11  14   2 
//
//                i   0  1  2  3  4  5  6  7  8  9 10 11 12 13 14
//    interleaver[i]  0 10  5  3 13  8  6  1 11  9  4 14 12  7  2
// ------------------------------------------------------------------------
// This program is complementary material for the book:
//
// R.H. Morelos-Zaragoza, The Art of Error Correcting Coding, Wiley, 2002.
//
// ISBN 0471 49581 6
//
// This and other programs are available at http://the-art-of-ecc.com
//
// You may use this program for academic and personal purposes only. 
// If this program is used to perform simulations whose results are 
// published in a journal or book, please refer to the book above.
//
// The use of this program in a commercial product requires explicit
// written permission from the author. The author is not responsible or 
// liable for damage or loss that may be caused by the use of this program. 
//
// Copyright (c) 2002. Robert H. Morelos-Zaragoza. All rights reserved.
// ------------------------------------------------------------------------

#include <stdio.h>
#include <math.h>
#include <float.h>
#include <limits.h>
#define NMAX 16384
#define NM2    512

main(int argc, char *argv[])
{

int interleaver[NMAX];
int array[NM2][NM2];
int temp[NMAX];
int i, j, position;
int N1, N2;
int N;                                 // Interleaver length
int D;                                 // Delay, see text p. 116
char name1[40];
FILE *fp1;

  // Command line processing
  if (argc != 5)
    {
      printf("Usage %s N1  N2  D  INT_file\n", argv[0]);
      exit(0);
    }

  sscanf(argv[1],"%d", &N1);
  sscanf(argv[2],"%d", &N2);
  sscanf(argv[3],"%d", &D);
  sscanf(argv[4],"%s", name1);

  N = N1*N2;

  fp1 = fopen(name1,"w");

  // Write columnwise
  for (i=0; i<N; i++)
    array[i%N1][i/N1] = i;

  for (i=0; i<N1; i++) {
    for (j=0; j<N2; j++)
      printf("%3d ", array[i][j]);
    printf("\n");
    }
  printf("\n");

  for (i=0; i<N1; i++) 
    {
      for (j=0; j<N2; j++)
        temp[j] = array[i][j];
      for (j=0; j<N2; j++)
        array[i][(i*D+j)%N2] = temp[j];
    }

  for (i=0; i<N1; i++) {
    for (j=0; j<N2; j++)
      printf("%3d ", array[i][j]);
    printf("\n");
    }
  printf("\n");

  // Read off columnwise
  for (i=0; i<N; i++)
    {
      position = array[i%N1][i/N1];
      interleaver[i] = position;
    }    

  for (i=0; i<N; i++)
    {
      fprintf(fp1, "%d\n", interleaver[i]);
      printf("%5d -> %5d\n",i,interleaver[i]);
    }

  fclose(fp1);

}