yafox
/
minimodem-mirror
1
0
Fork 0
Code Issues Pull Requests Releases Wiki Activity

fsk new confidence equation

This commit is contained in:
Kamal Mostafa 2011-06-04 16:31:26 -07:00
parent 1e96d42d16
commit 3522182394
1 changed files with 34 additions and 13 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

47
src/fsk.c
View File

@ -180,7 +180,7 @@ fsk_frame_decode( fsk_plan *fskp, float *samples, unsigned int frame_nsamples,
* collect the n_data_bits
*/
float s_str, p_str, i_str, d_str;
float s_str, p_str, i_str;
unsigned int bit;
debug_log("\t\tstart ");
@ -213,18 +213,40 @@ fsk_frame_decode( fsk_plan *fskp, float *samples, unsigned int frame_nsamples,
unsigned int bits_out = 0;
int i;
float d_str[32];
for ( i=0; i<fskp->n_data_bits; i++ ) {
debug_log("\t\tdata ");
unsigned int begin_databit = (float)(samples_per_bit * (i+2) + 0.5);
fsk_bit_analyze(fskp, samples+begin_databit, bit_nsamples,
&bit, &d_str);
v += d_str;
&bit, &d_str[i]);
v += d_str[i];
bits_out |= bit << i;
}
*bits_outp = bits_out;
debug_log( "v=%f\n", v );
return v;
/* Compute frame decode confidence as the inverse of the average
* bit-strength delta from the average bit-strength. (whew).*/
v /= fskp->n_frame_bits; /* v = average bit-strength */
/*
* Filter out noise below FSK_MIN_STRENGTH threshold
*/
#define FSK_MIN_STRENGTH 0.05
if ( v < FSK_MIN_STRENGTH )
return 0.0;
float confidence = 0;
confidence += 1.0 - fabs(i_str - v);
confidence += 1.0 - fabs(s_str - v);
confidence += 1.0 - fabs(p_str - v);
for ( i=0; i<fskp->n_data_bits; i++ ) {
confidence += 1.0 - fabs(d_str[i] - v);
}
confidence /= fskp->n_frame_bits;
debug_log( "frame decode confidence=%f\n", confidence );
return confidence;
}
@ -239,17 +261,17 @@ fsk_find_frame( fsk_plan *fskp, float *samples, unsigned int frame_nsamples,
{
unsigned int t;
unsigned int best_t = 0;
float best_v = 0.0;
float best_c = 0.0;
unsigned int best_bits = 0;
for ( t=0; t<try_max_nsamples; t+=try_step_nsamples )
{
float v;
float c;
unsigned int bits_out = 0;
debug_log("try fsk_frame_decode(skip=%+d)\n", t);
v = fsk_frame_decode(fskp, samples+t, frame_nsamples, &bits_out);
if ( best_v < v ) {
c = fsk_frame_decode(fskp, samples+t, frame_nsamples, &bits_out);
if ( best_c < c ) {
best_t = t;
best_v = v;
best_c = c;
best_bits = bits_out;
}
}
@ -257,8 +279,7 @@ fsk_find_frame( fsk_plan *fskp, float *samples, unsigned int frame_nsamples,
*bits_outp = best_bits;
*frame_start_outp = best_t;
/* The confidence equation */
float confidence = best_v / fskp->n_frame_bits;
float confidence = best_c;
debug_log("FSK_FRAME datum='%c' (0x%02x) c=%f t=%d\n",
isprint(best_bits)||isspace(best_bits) ? best_bits : '.',
@ -418,7 +439,7 @@ debug_log( "--------------------------\n");
&frame_start_sample
);
#define FSK_MIN_CONFIDENCE 0.05
#define FSK_MIN_CONFIDENCE 0.5 /* not critical */
unsigned int advance;