mirror of
https://github.com/saitohirga/WSJT-X.git
synced 2024-11-22 20:28:42 -05:00
12d5ec8902
git-svn-id: svn+ssh://svn.code.sf.net/p/wsjt/wsjt/branches/wsjtx@6241 ab8295b8-cf94-4d9e-aec4-7959e3be5d79
244 lines
6.7 KiB
C
244 lines
6.7 KiB
C
/*
|
|
sfrsd2.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 and Joe Taylor K1JT
|
|
*/
|
|
|
|
#include <stdio.h>
|
|
#include <stdlib.h>
|
|
#include <unistd.h>
|
|
#include <time.h>
|
|
#include <string.h>
|
|
#include "rs2.h"
|
|
|
|
static void *rs;
|
|
|
|
void sfrsd2_(int mrsym[], int mrprob[], int mr2sym[], int mr2prob[],
|
|
int* ntrials0, int* verbose0, int correct[], int param[],
|
|
int indexes[], double tt[], int ntry[])
|
|
{
|
|
int rxdat[63], rxprob[63], rxdat2[63], rxprob2[63];
|
|
int workdat[63],workdat2[63];
|
|
int era_pos[51];
|
|
int c, i, j, numera, nmr2, nerr, nn=63, kk=12;
|
|
FILE *datfile, *logfile;
|
|
int ntrials = *ntrials0;
|
|
int verbose = *verbose0;
|
|
int nhard=0,nhard_min=32768,nsoft=0,nsoft_min=32768, ncandidates;
|
|
int ngmd,nera_best;
|
|
clock_t t0=0,t1=0;
|
|
int perr[8][8] = {
|
|
12, 31, 44, 52, 60, 57, 50, 50,
|
|
28, 38, 49, 58, 65, 69, 64, 80,
|
|
40, 41, 53, 62, 66, 73, 76, 81,
|
|
50, 53, 53, 64, 70, 76, 77, 81,
|
|
50, 50, 52, 60, 71, 72, 77, 84,
|
|
50, 50, 56, 62, 67, 73, 81, 85,
|
|
50, 50, 71, 62, 70, 77, 80, 85,
|
|
50, 50, 62, 64, 71, 75, 82, 87};
|
|
|
|
int pmr2[8][8] = {
|
|
4, 8, 9, 7, 6, 0, 0, 0,
|
|
13, 18, 15, 11, 9, 7, 5, 0,
|
|
0, 23, 21, 15, 12, 10, 7, 4,
|
|
0, 34, 28, 20, 16, 14, 11, 7,
|
|
0, 20, 26, 25, 19, 14, 12, 9,
|
|
0, 0, 28, 27, 22, 19, 14, 11,
|
|
0, 0, 40, 29, 29, 23, 18, 12,
|
|
0, 0, 40, 35, 31, 21, 20, 13};
|
|
|
|
if(verbose) {
|
|
logfile=fopen("sfrsd.log","a");
|
|
if( !logfile ) {
|
|
printf("Unable to open sfrsd.log\n");
|
|
exit(1);
|
|
}
|
|
}
|
|
|
|
// 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);
|
|
|
|
// 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];
|
|
for (i=0; i<63; i++) {
|
|
indexes[i]=i;
|
|
probs[i]=rxprob[i];
|
|
}
|
|
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 ) {
|
|
if(verbose) fprintf(logfile," BM decode nerrors= %3d : ",nerr);
|
|
memcpy(correct,workdat,63*sizeof(int));
|
|
ngmd=-1;
|
|
param[0]=0;
|
|
param[1]=0;
|
|
param[2]=0;
|
|
param[3]=0;
|
|
param[4]=0;
|
|
return;
|
|
}
|
|
|
|
/*
|
|
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".
|
|
*/
|
|
|
|
#ifdef WIN32
|
|
srand(0xdeadbeef);
|
|
#else
|
|
srandom(0xdeadbeef);
|
|
#endif
|
|
|
|
float ratio, ratio0[63];
|
|
int threshe, thresh2, nsum;
|
|
int thresh0[63],thresh1[63], mr2flag;
|
|
ncandidates=0;
|
|
nsum=0;
|
|
int ii,jj;
|
|
for (i=0; i<nn; i++) {
|
|
nsum=nsum+rxprob[i];
|
|
j = indexes[62-i];
|
|
ratio = (float)rxprob2[j]/(float)rxprob[j];
|
|
ratio0[i]=ratio;
|
|
ii = 7.999*ratio;
|
|
jj = (62-i)/8;
|
|
thresh0[i] = 1.3*perr[ii][jj];
|
|
thresh1[i] = 0.4*pmr2[ii][jj];
|
|
}
|
|
if(nsum==0) return;
|
|
|
|
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.
|
|
Run through the ranked symbols, starting with the worst, i=0.
|
|
NB: j is the symbol-vector index of the symbol with rank i.
|
|
*/
|
|
numera=0;
|
|
nmr2=0;
|
|
for (i=0; i<nn; i++) {
|
|
j = indexes[62-i];
|
|
threshe=thresh0[i];
|
|
thresh2=thresh1[i];
|
|
long int ir, ir2;
|
|
#ifdef WIN32
|
|
ir=rand();
|
|
ir2=rand();
|
|
#else
|
|
ir=random();
|
|
ir2=random();
|
|
#endif
|
|
if( ((ir % 100) < threshe ) && (numera+2*nmr2) < 51 ) {
|
|
era_pos[numera]=j;
|
|
numera=numera+1;
|
|
}
|
|
if( ((ir2 % 100) < thresh2) && (numera+2*nmr2)<51) {
|
|
workdat[j]=rxdat2[j];
|
|
nmr2=nmr2+1;
|
|
}
|
|
}
|
|
t0=clock();
|
|
// rs=init_rs_int(symsize, gfpoly, fcr, prim, nroots, 1);
|
|
nerr=decode_rs_int(rs,workdat,era_pos,numera,1);
|
|
t1=clock();
|
|
tt[0]+=(double)(t1-t0)/CLOCKS_PER_SEC;
|
|
|
|
if( nerr >= 0 ) {
|
|
ncandidates=ncandidates+1;
|
|
nhard=0;
|
|
nsoft=0;
|
|
for (i=0; i<63; i++) {
|
|
if(workdat[i] != rxdat[i]) {
|
|
nhard=nhard+1;
|
|
if(workdat[i] != rxdat2[i]) {
|
|
nsoft=nsoft+rxprob[i];
|
|
}
|
|
}
|
|
}
|
|
nsoft=63*nsoft/nsum;
|
|
if((nsoft < 33) && (nhard < 43) && (nhard+nsoft) < 74) { //???
|
|
if( (nsoft < nsoft_min) ) {
|
|
nsoft_min=nsoft;
|
|
nhard_min=nhard;
|
|
memcpy(correct,workdat,63*sizeof(int));
|
|
ngmd=0;
|
|
nera_best=numera;
|
|
ntry[0]=k;
|
|
}
|
|
}
|
|
if(nsoft_min < 27) break;
|
|
if((nsoft_min < 32) && (nhard_min < 43) &&
|
|
(nhard_min+nsoft_min) < 74) break;
|
|
}
|
|
if(k == ntrials-1) ntry[0]=k+1;
|
|
}
|
|
|
|
if(verbose) fprintf(logfile,
|
|
"%d trials and %d candidates after stochastic loop\n",k,ncandidates);
|
|
|
|
if( (ncandidates >= 0) && (nsoft_min < 36) && (nhard_min < 44) ) {
|
|
if(verbose) {
|
|
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,"**** ncandidates %d nhard %d nsoft %d nsum %d\n",
|
|
ncandidates,nhard_min,nsoft_min,nsum);
|
|
}
|
|
} else {
|
|
nhard_min=-1;
|
|
}
|
|
|
|
if(verbose) {
|
|
fprintf(logfile,"exiting sfrsd\n");
|
|
fclose(logfile);
|
|
}
|
|
param[0]=ncandidates;
|
|
param[1]=nhard_min;
|
|
param[2]=nsoft_min;
|
|
param[3]=nera_best;
|
|
param[4]=ngmd;
|
|
if(param[0]==0) param[2]=-1;
|
|
return;
|
|
}
|