WSJT-X/lib/sfrsd/sfrsd.c

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/*
sfrsd.c
A soft-decision decoder for the JT65 (63,12) Reed-Solomon code.
This decoding scheme is built around Phil Karn's Berlekamp-Massey
errors and erasures decoder. The approach is inspired by a number of
publications, including the stochastic Chase decoder described
in "Stochastic Chase Decoding of Reed-Solomon Codes", by Leroux et al.,
IEEE Communications Letters, Vol. 14, No. 9, September 2010 and
"Soft-Decision Decoding of Reed-Solomon Codes Using Successive Error-
and-Erasure Decoding," by Soo-Woong Lee and B. V. K. Vijaya Kumar.
Steve Franke K9AN, Urbana IL, September 2015
*/
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <time.h>
#include <string.h>
#include "rs.h"
#include "init_random_seed.h"
static void *rs;
//***************************************************************************
void usage(void)
{
printf("Usage: sfrsd [options...] <path to kvasd.dat>\n");
printf(" input file should be in kvasd format\n");
printf("\n");
printf("Options:\n");
printf(" -n number of random erasure vectors to try\n");
printf(" -v verbose\n");
}
int main(int argc, char *argv[]){
extern char *optarg;
extern int optind;
int rxdat[63], rxprob[63], rxdat2[63], rxprob2[63];
int workdat[63], correct[63];
int era_pos[51];
int c, i, numera, nerr, nn=63, kk=12;
char *infile;
FILE *datfile, *logfile;
int nsec, maxe, nads;
float xlambda;
int mrsym[63],mrprob[63],mr2sym[63],mr2prob[63];
int nsec2,ncount,dat4[12],bestdat[12];
int ntrials=10000;
int verbose=0;
int nhard=0,nhard_min=32768,nsoft=0,nsoft_min=32768, ncandidates;
while ( (c = getopt(argc, argv, "n:qv")) !=-1 ) {
switch (c) {
case 'n':
ntrials=(int)strtof(optarg,NULL);
printf("ntrials set to %d\n",ntrials);
break;
case 'v':
verbose=1;
break;
case 'q': //accept (and ignore) -q option for WSJT10 compatibility
break;
case '?':
usage();
exit(1);
}
}
if( optind+1 > argc) {
// usage();
// exit(1);
infile="kvasd.dat";
} else {
infile=argv[optind];
}
logfile=fopen("/tmp/sfrsd.log","a");
if( !logfile ) {
printf("Unable to open sfrsd.log\n");
exit(1);
}
datfile=fopen(infile,"rb");
if( !datfile ) {
printf("Unable to open kvasd.dat\n");
exit(1);
} else {
fread(&nsec,sizeof(int),1,datfile);
fread(&xlambda,sizeof(float),1,datfile);
fread(&maxe,sizeof(int),1,datfile);
fread(&nads,sizeof(int),1,datfile);
fread(&mrsym,sizeof(int),63,datfile);
fread(&mrprob,sizeof(int),63,datfile);
fread(&mr2sym,sizeof(int),63,datfile);
fread(&mr2prob,sizeof(int),63,datfile);
fread(&nsec2,sizeof(int),1,datfile);
fread(&ncount,sizeof(int),1,datfile);
// printf("ncount %d\n",ncount);
fread(&dat4,sizeof(int),12,datfile);
fclose(datfile);
}
// initialize the ka9q reed solomon encoder/decoder
unsigned int symsize=6, gfpoly=0x43, fcr=3, prim=1, nroots=51;
rs=init_rs_int(symsize, gfpoly, fcr, prim, nroots, 0);
/* // debug
int revdat[12], parity[51], correct[63];
for (i=0; i<12; i++) {
revdat[i]=dat4[11-i];
printf("%d ",revdat[i]);
}
printf("\n");
encode_rs_int(rs,revdat,parity);
for (i=0; i<63; i++) {
if( i<12 ) {
correct[i]=revdat[i];
printf("%d ",parity[i]);
} else {
correct[i]=parity[i-12];
}
}
printf("\n");
*/
// reverse the received symbol vector for bm decoder
for (i=0; i<63; i++) {
rxdat[i]=mrsym[62-i];
rxprob[i]=mrprob[62-i];
rxdat2[i]=mr2sym[62-i];
rxprob2[i]=mr2prob[62-i];
}
// sort the mrsym probabilities to find the least reliable symbols
int k, pass, tmp, nsym=63;
int probs[63], indexes[63];
for (i=0; i<63; i++) {
indexes[i]=i;
probs[i]=rxprob[i]; // must un-comment sfrsd metrics in demod64a
}
for (pass = 1; pass <= nsym-1; pass++) {
for (k = 0; k < nsym - pass; k++) {
if( probs[k] < probs[k+1] ) {
tmp = probs[k];
probs[k] = probs[k+1];
probs[k+1] = tmp;
tmp = indexes[k];
indexes[k] = indexes[k+1];
indexes[k+1] = tmp;
}
}
}
// see if we can decode using BM HDD (and calculate the syndrome vector)
memset(era_pos,0,51*sizeof(int));
numera=0;
memcpy(workdat,rxdat,sizeof(rxdat));
nerr=decode_rs_int(rs,workdat,era_pos,numera,1);
if( nerr >= 0 ) {
fprintf(logfile," BM decode nerrors= %3d : ",nerr);
for(i=0; i<12; i++) printf("%2d ",workdat[11-i]);
fprintf(logfile,"\n");
fclose(logfile);
exit(0);
}
// generate random erasure-locator vectors and see if any of them
// decode. This will generate a list of potential codewords. The
// "soft" distance between each codeword and the received word is
// used to decide which codeword is "best".
//
init_random_seed();
float p_erase;
int thresh, nsum;
ncandidates=0;
for( k=0; k<ntrials; k++) {
memset(era_pos,0,51*sizeof(int));
memcpy(workdat,rxdat,sizeof(rxdat));
// mark a subset of the symbols as erasures
numera=0;
for (i=0; i<nn; i++) {
p_erase=0.0;
if( probs[62-i] >= 255 ) {
p_erase = 0.5;
} else if ( probs[62-i] >= 196 ) {
p_erase = 0.6;
} else if ( probs[62-i] >= 128 ) {
p_erase = 0.6;
} else if ( probs[62-i] >= 32 ) {
p_erase = 0.6;
} else {
p_erase = 0.8;
}
thresh = p_erase*100;
long int ir;
ir=rand();
if( ((ir % 100) < thresh ) && numera < 51 ) {
era_pos[numera]=indexes[62-i];
numera=numera+1;
}
}
nerr=decode_rs_int(rs,workdat,era_pos,numera,0);
if( nerr >= 0 ) {
ncandidates=ncandidates+1;
for(i=0; i<12; i++) dat4[i]=workdat[11-i];
// fprintf(logfile,"loop1 decode nerr= %3d : ",nerr);
// for(i=0; i<12; i++) fprintf(logfile, "%2d ",dat4[i]);
// fprintf(logfile,"\n");
nhard=0;
nsoft=0;
nsum=0;
for (i=0; i<63; i++) {
nsum=nsum+rxprob[i];
if( workdat[i] != rxdat[i] ) {
nhard=nhard+1;
nsoft=nsoft+rxprob[i];
}
}
if( nsum != 0 ) {
nsoft=63*nsoft/nsum;
if( (nsoft < nsoft_min) ) {
nsoft_min=nsoft;
nhard_min=nhard;
memcpy(bestdat,dat4,12*sizeof(int));
memcpy(correct,workdat,63*sizeof(int));
}
} else {
fprintf(logfile,"error - nsum %d nsoft %d nhard %d\n",nsum,nsoft,nhard);
}
// if( ncandidates >= 5000 ) {
if( ncandidates >= ntrials/2 ) {
break;
}
}
}
fprintf(logfile,"%d candidates after stochastic loop\n",ncandidates);
// do Forney Generalized Minimum Distance pattern
for (k=0; k<25; k++) {
memset(era_pos,0,51*sizeof(int));
numera=2*k;
for (i=0; i<numera; i++) {
era_pos[i]=indexes[62-i];
}
memcpy(workdat,rxdat,sizeof(rxdat));
nerr=decode_rs_int(rs,workdat,era_pos,numera,0);
if( nerr >= 0 ) {
ncandidates=ncandidates+1;
for(i=0; i<12; i++) dat4[i]=workdat[11-i];
// fprintf(logfile,"GMD decode nerr= %3d : ",nerr);
// for(i=0; i<12; i++) fprintf(logfile, "%2d ",dat4[i]);
// fprintf(logfile,"\n");
nhard=0;
nsoft=0;
nsum=0;
for (i=0; i<63; i++) {
nsum=nsum+rxprob[i];
if( workdat[i] != rxdat[i] ) {
nhard=nhard+1;
nsoft=nsoft+rxprob[i];
}
}
if( nsum != 0 ) {
nsoft=63*nsoft/nsum;
if( (nsoft < nsoft_min) ) {
nsoft_min=nsoft;
nhard_min=nhard;
memcpy(bestdat,dat4,12*sizeof(int));
memcpy(correct,workdat,63*sizeof(int));
}
} else {
fprintf(logfile,"error - nsum %d nsoft %d nhard %d\n",nsum,nsoft,nhard);
}
// if( ncandidates >=5000 ) {
if( ncandidates >= ntrials/2 ) {
break;
}
}
}
fprintf(logfile,"%d candidates after GMD\n",ncandidates);
if( (ncandidates >= 0) && (nsoft_min < 36) && (nhard_min < 44) ) {
for (i=0; i<63; i++) {
fprintf(logfile,"%3d %3d %3d %3d %3d %3d\n",i,correct[i],rxdat[i],rxprob[i],rxdat2[i],rxprob2[i]);
// fprintf(logfile,"%3d %3d %3d %3d %3d\n",i,workdat[i],rxdat[i],rxprob[i],rxdat2[i],rxprob2[i]);
}
fprintf(logfile,"**** ncandidates %d nhard %d nsoft %d nsum %d\n",ncandidates,nhard_min,nsoft_min,nsum);
} else {
nhard_min=-1;
memset(bestdat,0,12*sizeof(int));
}
datfile=fopen(infile,"wb");
if( !datfile ) {
printf("Unable to open kvasd.dat\n");
return 1;
} else {
fwrite(&nsec,sizeof(int),1,datfile);
fwrite(&xlambda,sizeof(float),1,datfile);
fwrite(&maxe,sizeof(int),1,datfile);
fwrite(&nads,sizeof(int),1,datfile);
fwrite(&mrsym,sizeof(int),63,datfile);
fwrite(&mrprob,sizeof(int),63,datfile);
fwrite(&mr2sym,sizeof(int),63,datfile);
fwrite(&mr2prob,sizeof(int),63,datfile);
fwrite(&nsec2,sizeof(int),1,datfile);
fwrite(&nhard_min,sizeof(int),1,datfile);
fwrite(&bestdat,sizeof(int),12,datfile);
fclose(datfile);
}
fprintf(logfile,"exiting sfrsd\n");
fflush(logfile);
fclose(logfile);
exit(0);
}