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fsk: confidence considers start/stop bits

This commit is contained in:
Kamal Mostafa 2011-06-21 12:13:47 -07:00
parent 15bb83ee9b
commit 9002cf2694
1 changed files with 24 additions and 31 deletions
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55
src/fsk.c
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@ -128,47 +128,24 @@ fsk_bit_analyze( fsk_plan *fskp, float *samples, unsigned int bit_nsamples,
/* returns confidence value [0.0 to 1.0] */
static float
static void
fsk_bits_analyze( fsk_plan *fskp, float *samples, float samples_per_bit,
unsigned int *bits_outp )
unsigned int *bits_outp, float *bit_strengths_outp )
{
unsigned int bit_nsamples = (float)(samples_per_bit + 0.5);
unsigned int nbits = fskp->n_data_bits;
float v = 0;
unsigned int bits_out = 0;
int i;
float d_str[32];
for ( i=0; i<nbits; i++ ) {
unsigned int begin_databit = (float)(samples_per_bit * i + 0.5);
unsigned int bit;
debug_log("\t\tdata begin_data_bit=%u ", begin_databit);
fsk_bit_analyze(fskp, samples+begin_databit, bit_nsamples,
&bit, &d_str[i]);
v += d_str[i];
&bit, &bit_strengths_outp[i]);
bits_out |= bit << i;
}
*bits_outp = bits_out;
/* Compute frame decode confidence as the inverse of the average
* bit-strength delta from the average bit-strength. (whew).*/
v /= nbits; /* 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;
for ( i=0; i<nbits; i++ ) {
confidence += 1.0 - fabs(d_str[i] - v);
}
confidence /= nbits;
debug_log(__func__ " confidence=%f\n", confidence );
return confidence;
}
@ -233,12 +210,28 @@ fsk_frame_analyze( fsk_plan *fskp, float *samples, float samples_per_bit,
return 0.0;
v += i_str;
// FIXME -- we're not actually even using 'v' from above
// Analyze the actual data payload bits
float confidence;
confidence = fsk_bits_analyze(fskp, samples+begin_databits,
samples_per_bit, bits_outp);
float databit_strengths[32];
fsk_bits_analyze(fskp, samples+begin_databits, samples_per_bit,
bits_outp, databit_strengths);
// computer average bit strength 'v'
int i;
for ( i=0; i<fskp->n_data_bits; i++ )
v += databit_strengths[i];
v /= (fskp->n_data_bits + 3);
#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(databit_strengths[i] - v);
confidence /= (fskp->n_data_bits + 3);
return confidence;
}