/* 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");}