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fsk: CONFIDENCE_ALGO 3 (worst divergence) 

CONFIDENCE_ALGO 3 (worst divergence):
 - single worst diverging bit in the frame
 - amplitude normalized
 - drop AVOID_TRANSIENT
This commit is contained in:
Kamal Mostafa 2011-07-08 08:03:31 -07:00
parent cb3e81e576
commit 845c3e1be6
2 changed files with 23 additions and 29 deletions
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50
src/fsk.c
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@ -186,16 +186,17 @@ fsk_frame_analyze( fsk_plan *fskp, float *samples, float samples_per_bit,
v += bit_strengths[bitnum];
}
// float i_str = bit_strengths[0];
float s_str = bit_strengths[1];
float p_str = bit_strengths[fskp->n_data_bits + 2];
#define AVOID_TRANSIENTS 0.7
// Note: CONFIDENCE_ALGO 3 does not need AVOID_TRANSIENTS
// #define AVOID_TRANSIENTS 0.7
//
#ifdef AVOID_TRANSIENTS
/* Compare strength of stop bit and start bit, to avoid detecting
* a transient as a start bit, as often results in a single false
* character when the mark "leader" tone begins. Require that the
* diff between start bit and stop bit strength not be "large". */
//float i_str = bit_strengths[0];
float s_str = bit_strengths[1];
float p_str = bit_strengths[fskp->n_data_bits + 2];
if ( fabs(s_str-p_str) > (s_str * AVOID_TRANSIENTS) ) {
debug_log(" avoid transient\n");
return 0.0;
@ -220,33 +221,23 @@ fsk_frame_analyze( fsk_plan *fskp, float *samples, float samples_per_bit,
if ( v < FSK_MIN_STRENGTH )
return 0.0;
#define CONFIDENCE_ALGO 3
float worst_divergence = 0;
int i;
for ( i=0; i<n_bits; i++ ) {
float normalized_bit_str = bit_strengths[i] / v;
float divergence = fabs(1.0 - normalized_bit_str);
if ( worst_divergence < divergence )
worst_divergence = divergence;
}
float confidence = 1.0 - worst_divergence;
if ( confidence <= 0.0 )
return 0.0;
#define CONFIDENCE_ALGO 2
#if ( CONFIDENCE_ALGO == 1 )
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(databit_strengths[i] - v);
confidence /= (fskp->n_data_bits + 3);
#elif ( CONFIDENCE_ALGO == 2 )
float confidence = 0;
for ( i=0; i<n_bits; i++ )
confidence += bit_strengths[i];
confidence /= n_bits;
#endif
*bits_outp = 0;
// FIXME: databits at hardcoded offset of +2
// for ( i=0; i<fskp->n_data_bits; i++ )
// *bits_outp |= bit_values[i+2] << i;
for ( i=0; i<n_bits; i++ )
*bits_outp |= bit_values[i] << i;
@ -288,6 +279,9 @@ fsk_find_frame( fsk_plan *fskp, float *samples, unsigned int frame_nsamples,
float confidence = best_c;
if ( confidence == 0 )
return 0;
// FIXME? hardcoded chop off framing bits for debug
#ifdef FSK_DEBUG
unsigned char bitchar = ( best_bits >> 2 ) & 0xFF;

2
src/minimodem.c
View File

@ -601,7 +601,7 @@ main( int argc, char*argv[] )
else
bits = ( bits >> 2 ) & 0xFF;
#define FSK_MIN_CONFIDENCE 0.05
#define FSK_MIN_CONFIDENCE 0.50
#define FSK_MAX_NOCONFIDENCE_BITS 20
if ( confidence <= FSK_MIN_CONFIDENCE ) {