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fsk: calc separate divergences for mark and space bits 

Calculate and consider separate signal-strength divergence values for
mark and space bits, so that imbalanced (but consistent) mark/space
strengths do not drive down confidence.

Note: This change makes all existing test cases yield very slightly
higher confidence values.
This commit is contained in:
Kamal Mostafa 2014-11-16 10:26:28 -08:00
parent 746f0f6c7a
commit 40f1d50cbd
1 changed files with 18 additions and 2 deletions
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20
src/fsk.c
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@ -269,6 +269,8 @@ fsk_frame_analyze( fsk_plan *fskp, float *samples, float samples_per_bit,
#if CONFIDENCE_ALGO == 5 || CONFIDENCE_ALGO == 6
float total_bit_sig = 0.0, total_bit_noise = 0.0;
float avg_mark_sig = 0.0, avg_space_sig = 0.0;
unsigned int n_mark = 0, n_space = 0;
for ( bitnum=0; bitnum<n_bits; bitnum++ ) {
// Deal with floating point data type quantization noise...
// If total_bit_noise <= FLT_EPSILON, then assume it to be 0.0,
@ -276,6 +278,14 @@ fsk_frame_analyze( fsk_plan *fskp, float *samples, float samples_per_bit,
total_bit_sig += bit_sig_mags[bitnum];
if ( bit_noise_mags[bitnum] > FLT_EPSILON )
total_bit_noise += bit_noise_mags[bitnum];
if ( bit_values[bitnum] == 1 ) {
avg_mark_sig += bit_sig_mags[bitnum];
n_mark++;
} else {
avg_space_sig += bit_sig_mags[bitnum];
n_space++;
}
}
// Compute the "frame SNR"
@ -284,12 +294,18 @@ fsk_frame_analyze( fsk_plan *fskp, float *samples, float samples_per_bit,
// Compute avg bit sig and noise magnitudes
float avg_bit_sig = total_bit_sig / n_bits;
// Compute separate avg bit sig for mark and space
if ( n_mark )
avg_mark_sig /= n_mark;
if ( n_space )
avg_space_sig /= n_space;
#if CONFIDENCE_ALGO == 6
// Compute average "divergence": bit_mag_divergence / other_bits_mag
float divergence = 0.0;
for ( bitnum=0; bitnum<n_bits; bitnum++ ) {
float avg_bit_sig_other = (total_bit_sig - fabs(bit_sig_mags[bitnum]))
/ (n_bits - 1);
float avg_bit_sig_other;
avg_bit_sig_other = bit_values[bitnum] ? avg_mark_sig : avg_space_sig;
divergence += fabs(bit_sig_mags[bitnum] - avg_bit_sig_other)
/ avg_bit_sig_other;
}