vittest.c

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/* Test a soft decision viterbi decoder
 * Copyright 1999 Phil Karn, KA9Q
 * May be used under the terms of the GNU Public License
 */

#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#include <memory.h>

void modnoise(unsigned char *,unsigned int,double,double);
int viterbi(
long *metric,           /* Final path metric (returned value) */
unsigned char *data,	/* Decoded output data */
unsigned char *symbols,	/* Raw deinterleaved input symbols */
unsigned int nbits,	/* Number of output bits; 2*(nbits+6) input symbols will be read */
int mettab[2][256],	/* Metric table, [sent sym][rx symbol] */
unsigned int startstate,         /* Encoder starting state */
unsigned int endstate            /* Encoder ending state */
);

/* Convolutionally encode data into binary symbols */
int encode(
unsigned char *symbols,
unsigned char *data,
unsigned int nbytes,
unsigned int startstate,
unsigned int endstate
);



/* Lookup table giving count of 1 bits for integers 0-255 */
unsigned char Bitcnt[] = {
 0, 1, 1, 2, 1, 2, 2, 3,
 1, 2, 2, 3, 2, 3, 3, 4,
 1, 2, 2, 3, 2, 3, 3, 4,
 2, 3, 3, 4, 3, 4, 4, 5,
 1, 2, 2, 3, 2, 3, 3, 4,
 2, 3, 3, 4, 3, 4, 4, 5,
 2, 3, 3, 4, 3, 4, 4, 5,
 3, 4, 4, 5, 4, 5, 5, 6,
 1, 2, 2, 3, 2, 3, 3, 4,
 2, 3, 3, 4, 3, 4, 4, 5,
 2, 3, 3, 4, 3, 4, 4, 5,
 3, 4, 4, 5, 4, 5, 5, 6,
 2, 3, 3, 4, 3, 4, 4, 5,
 3, 4, 4, 5, 4, 5, 5, 6,
 3, 4, 4, 5, 4, 5, 5, 6,
 4, 5, 5, 6, 5, 6, 6, 7,
 1, 2, 2, 3, 2, 3, 3, 4,
 2, 3, 3, 4, 3, 4, 4, 5,
 2, 3, 3, 4, 3, 4, 4, 5,
 3, 4, 4, 5, 4, 5, 5, 6,
 2, 3, 3, 4, 3, 4, 4, 5,
 3, 4, 4, 5, 4, 5, 5, 6,
 3, 4, 4, 5, 4, 5, 5, 6,
 4, 5, 5, 6, 5, 6, 6, 7,
 2, 3, 3, 4, 3, 4, 4, 5,
 3, 4, 4, 5, 4, 5, 5, 6,
 3, 4, 4, 5, 4, 5, 5, 6,
 4, 5, 5, 6, 5, 6, 6, 7,
 3, 4, 4, 5, 4, 5, 5, 6,
 4, 5, 5, 6, 5, 6, 6, 7,
 4, 5, 5, 6, 5, 6, 6, 7,
 5, 6, 6, 7, 6, 7, 7, 8,
};

main(argc,argv)
int argc;
char *argv[];
{
  double ebn0,esn0,noise;
  int mettab[2][256];
  int amp,nbits,nbytes,i;
  unsigned char *symbols;
  unsigned char *data,*decdata;
  unsigned long metric;
  long t,ntrials;
  long seed;
  extern char *optarg;
  unsigned long biterrs = 0;
  unsigned long framerrs = 0;
  int timetrial;
  int verbose = 0;
  int rate; /* 1/rate is the actual code rate */
  extern int Rate;
  
  amp = 100;
  ebn0 = 5.0;
  nbits = 1152;
  ntrials = 10;
  timetrial = 0;
  time(&seed);
  while((i = getopt(argc,argv,"a:e:n:N:qs:t")) != EOF){
    switch(i){
    case 'a':
      amp = atoi(optarg);	/* Signal amplitude in units */
      break;
    case 'e':
      ebn0 = atof(optarg);	/* Eb/N0 in dB */
      break;
    case 'n':
      nbits = atoi(optarg);	/* Number of data bits */
      break;
    case 'N':
      ntrials = atoi(optarg);
      break;
    case 's':
      seed = atoi(optarg);
      break;
    case 't':	/* Generate noise once, for decoder timing */
      timetrial = 1;
      break;
    case 'v':
      verbose++;
      break;
    case '?':
      usage();
      exit(1);
    }
  }
  nbytes = nbits/8;
  srandom(seed);
  
  esn0 = ebn0 - 10*log10((double)Rate);	/* Es/N0 in dB */	
  
  /* Compute noise voltage. The 0.5 factor accounts for BPSK seeing
   * only half the noise power, and the sqrt() converts power to
   * voltage.
   */
  noise = sqrt(0.5/pow(10.,esn0/10.));
  
  data = malloc(nbytes);
  decdata = malloc(nbytes);
  symbols = malloc((nbits+20)*Rate); /* 20 > max K */
  
  /* Generate metrics analytically, with gaussian pdf */	
  gen_met(mettab,amp,noise,0.,4);
  printf("metric table range %d to %d\n",mettab[0][0],mettab[1][0]);
  
  /* Generate data */
  memset(data,0,nbytes);	/* Default to all 0's */
  data[0] = 0x01;
  data[1] = 0x23;
  data[2] = 0x45;
  data[3] = 0x67;
  data[4] = 0x55;
  data[nbytes-4] = 0x55;
  data[nbytes-3] = 0xaa;
  data[nbytes-2] = 0xff;
  data[nbytes-1] = 0xff;
  
  i = 0;
  if(timetrial){
    encode(symbols,data,nbytes,0,0);
    modnoise(symbols,(nbits+20)*2,amp,noise);
    for(t = 1;t <= ntrials;t++)
      viterbi(&metric,decdata,symbols,nbits,mettab,0,0);
    printf("bits decoded = %ld\n",nbits*ntrials);
    exit(0);
  }
  printf("original data:\n",t);
  for(i=0;i<nbytes;i++)
    printf("%02x",data[i]);
  printf("\n");			
  for(t = 1;t <= ntrials;t++){
    /* Modulate and add noise */
    encode(symbols,data,nbytes,0,0);
    modnoise(symbols,(nbits+20)*Rate,amp,noise);
    viterbi(&metric,decdata,symbols,nbits,mettab,0,0);
    if(memcmp(data,decdata,nbytes) != 0){
      printf("frame %d decoded data:\n",t);
      for(i=0;i<nbytes;i++)
	printf("%02x",decdata[i]);
      printf("\n");
      framerrs++;
      for(i=0;i<nbytes;i++){
	biterrs += Bitcnt[data[i]^decdata[i]];
      }
    }
  }
  printf("Seed %ld Amplitude %d units, Eb/N0 = %lg dB\n",seed,amp,ebn0);
  printf("Amplitude %d units, Eb/N0 = %lg dB\n",amp,ebn0);
  printf("Frame length = %d bits, #frames = %ld, bits decoded = %ld\n",
	 nbits,ntrials,nbits*ntrials);
  printf("frame errors: %ld (%g)\n",framerrs,(double)framerrs/ntrials);
  printf("bit errors: %ld (%g)\n",biterrs,(double)biterrs/(nbits*ntrials));
}

usage()
{
  printf("Usage: vittest [options]\n");
  printf("Option&default	meaning\n");
  printf("-a 100		amplitude\n");
  printf("-e 5.0		Eb/N0 in dB\n");
  printf("-n 1152		trial frame size, bits\n");
  printf("-N 10		number of trials\n");
  printf("-s [cur time]	seed for random number generator\n\n");
  printf("-t		select timetest mode (default off)\n");
}