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fsk: MIN_MAGNITUDE noise limiter

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This commit is contained in:
Kamal Mostafa 2012-08-18 19:15:07 -07:00
parent 725355aa43
commit 076343a9c3
1 changed files with 18 additions and 1 deletions
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19
src/fsk.c
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@ -224,6 +224,17 @@ fsk_frame_analyze( fsk_plan *fskp, float *samples, float samples_per_bit,
if ( (expect_bits[bitnum] - '0') != bit_values[bitnum] ) if ( (expect_bits[bitnum] - '0') != bit_values[bitnum] )
return 0.0; /* does not match expected; abort frame analysis. */ return 0.0; /* does not match expected; abort frame analysis. */
// FSK_MIN_MAGNITUDE serves as a noise limiter
# define FSK_MIN_MAGNITUDE 0.10
# ifdef FSK_MIN_MAGNITUDE
// Performance hack: reject frame early if sig mag isn't even half
// of FSK_MIN_MAGNITUDE
if ( bit_sig_mags[bitnum] < FSK_MIN_MAGNITUDE/2.0 )
return 0.0; // too weak; abort frame analysis
# endif
} }
// Note: CONFIDENCE_ALGO 3 does not need AVOID_TRANSIENTS // Note: CONFIDENCE_ALGO 3 does not need AVOID_TRANSIENTS
@ -278,13 +289,19 @@ fsk_frame_analyze( fsk_plan *fskp, float *samples, float samples_per_bit,
// Compute the "frame SNR" // Compute the "frame SNR"
float snr = total_bit_sig / total_bit_noise; float snr = total_bit_sig / total_bit_noise;
#ifdef FSK_DEBUG
float avg_bit_sig = total_bit_sig / (n_bits-1); float avg_bit_sig = total_bit_sig / (n_bits-1);
#ifdef FSK_DEBUG
float avg_bit_noise = total_bit_noise / (n_bits-1); float avg_bit_noise = total_bit_noise / (n_bits-1);
debug_log(" snr=%.6f avg{ bit_sig=%.6f bit_noise=%.6f }\n", debug_log(" snr=%.6f avg{ bit_sig=%.6f bit_noise=%.6f }\n",
snr, avg_bit_sig, avg_bit_noise); snr, avg_bit_sig, avg_bit_noise);
#endif #endif
# ifdef FSK_MIN_MAGNITUDE
// noise limiter
if ( avg_bit_sig < FSK_MIN_MAGNITUDE )
return 0.0; // too weak; reject frame
# endif
// Frame confidence is the frame SNR // Frame confidence is the frame SNR
confidence = snr; confidence = snr;