fsk: confidence algo #6: "SNR * (1-divergence)"
Disabled all the hardcoded noise limiters.
This commit is contained in:
Kamal Mostafa
parent
23a44ce374
commit
1ed3b8465a
67
src/fsk.c
67
src/fsk.c
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@ -174,7 +174,7 @@ fsk_bit_analyze( fsk_plan *fskp, float *samples, unsigned int bit_nsamples,
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}
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/* returns confidence value [0.0 to 1.0] */
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/* returns confidence value [0.0 to INFINITY] */
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static float
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fsk_frame_analyze( fsk_plan *fskp, float *samples, float samples_per_bit,
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int n_bits, const char *expect_bits_string,
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@ -188,6 +188,11 @@ fsk_frame_analyze( fsk_plan *fskp, float *samples, float samples_per_bit,
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unsigned int bit_begin_sample;
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int bitnum;
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// various deprecated noise limiter schemes:
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//#define FSK_MIN_BIT_SNR 1.4
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//#define FSK_MIN_MAGNITUDE 0.10
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//#define FSK_AVOID_TRANSIENTS 0.7
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const char *expect_bits = expect_bits_string;
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/* pass #1 - process and check only the "required" (1/0) expect_bits */
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@ -206,8 +211,11 @@ fsk_frame_analyze( fsk_plan *fskp, float *samples, float samples_per_bit,
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if ( (expect_bits[bitnum] - '0') != bit_values[bitnum] )
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return 0.0; /* does not match expected; abort frame analysis. */
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// FSK_MIN_MAGNITUDE serves as a noise limiter
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# define FSK_MIN_MAGNITUDE 0.10
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#ifdef FSK_MIN_BIT_SNR
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float bit_snr = bit_sig_mags[bitnum] / bit_noise_mags[bitnum];
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if ( bit_snr < FSK_MIN_BIT_SNR )
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return 0.0;
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#endif
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# ifdef FSK_MIN_MAGNITUDE
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// Performance hack: reject frame early if sig mag isn't even half
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@ -215,13 +223,9 @@ fsk_frame_analyze( fsk_plan *fskp, float *samples, float samples_per_bit,
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if ( bit_sig_mags[bitnum] < FSK_MIN_MAGNITUDE/2.0 )
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return 0.0; // too weak; abort frame analysis
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# endif
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}
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// Note: CONFIDENCE_ALGO 3 does not need AVOID_TRANSIENTS
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#define AVOID_TRANSIENTS 0.7
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//
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#ifdef AVOID_TRANSIENTS
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#ifdef FSK_AVOID_TRANSIENTS
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// FIXME: fsk_frame_analyze shouldn't care about start/stop bits,
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// and this really is only correct for "10dd..dd1" format frames anyway:
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// FIXME: this is totally defective, if the checked bits weren't
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@ -232,7 +236,7 @@ fsk_frame_analyze( fsk_plan *fskp, float *samples, float samples_per_bit,
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* diff between start bit and stop bit strength not be "large". */
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float s_mag = bit_sig_mags[1]; // start bit
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float p_mag = bit_sig_mags[n_bits-1]; // stop bit
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if ( fabs(s_mag-p_mag) > (s_mag * AVOID_TRANSIENTS) ) {
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if ( fabs(s_mag-p_mag) > (s_mag * FSK_AVOID_TRANSIENTS) ) {
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debug_log(" avoid transient\n");
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return 0.0;
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}
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@ -248,17 +252,24 @@ fsk_frame_analyze( fsk_plan *fskp, float *samples, float samples_per_bit,
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&bit_values[bitnum],
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&bit_sig_mags[bitnum],
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&bit_noise_mags[bitnum]);
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#ifdef FSK_MIN_BIT_SNR
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float bit_snr = bit_sig_mags[bitnum] / bit_noise_mags[bitnum];
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if ( bit_snr < FSK_MIN_BIT_SNR )
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return 0.0;
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#endif
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}
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#define CONFIDENCE_ALGO 5
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//#define CONFIDENCE_ALGO 5
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#define CONFIDENCE_ALGO 6
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float confidence;
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#if CONFIDENCE_ALGO == 5
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#if CONFIDENCE_ALGO == 5 || CONFIDENCE_ALGO == 6
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float total_bit_sig = 0.0, total_bit_noise = 0.0;
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for ( bitnum=0; bitnum<(n_bits-1); bitnum++ ) {
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for ( bitnum=0; bitnum<n_bits; bitnum++ ) {
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// Deal with floating point data type quantization noise...
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// If total_bit_noise <= FLT_EPSILON, then assume it to be 0.0,
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// so that we end up with snr==inf.
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@ -270,23 +281,47 @@ fsk_frame_analyze( fsk_plan *fskp, float *samples, float samples_per_bit,
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// Compute the "frame SNR"
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float snr = total_bit_sig / total_bit_noise;
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float avg_bit_sig = total_bit_sig / (n_bits-1);
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// Compute avg bit sig and noise magnitudes
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float avg_bit_sig = total_bit_sig / n_bits;
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#if CONFIDENCE_ALGO == 6
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// Compute average "divergence": bit_mag_divergence / other_bits_mag
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float divergence = 0.0;
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for ( bitnum=0; bitnum<n_bits; bitnum++ ) {
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float avg_bit_sig_other = (total_bit_sig - fabs(bit_sig_mags[bitnum]))
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/ (n_bits - 1);
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divergence += fabs(bit_sig_mags[bitnum] - avg_bit_sig_other)
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/ avg_bit_sig_other;
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}
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divergence *= 2;
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divergence /= n_bits;
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#endif
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#ifdef FSK_DEBUG
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float avg_bit_noise = total_bit_noise / (n_bits-1);
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debug_log(" snr=%.6f avg{ bit_sig=%.6f bit_noise=%.6f (%s) }\n",
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float avg_bit_noise = total_bit_noise / n_bits;
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debug_log(" divg=%.3f snr=%.3f avg{bit_sig=%.3f bit_noise=%.3f(%s)}\n",
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# if CONFIDENCE_ALGO == 6
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divergence,
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# else
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0.0,
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# endif
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snr, avg_bit_sig, avg_bit_noise,
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avg_bit_noise == 0.0 ? "zero" : "non-zero"
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);
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#endif
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# ifdef FSK_MIN_MAGNITUDE
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// noise limiter
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if ( avg_bit_sig < FSK_MIN_MAGNITUDE )
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return 0.0; // too weak; reject frame
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# endif
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#if CONFIDENCE_ALGO == 6
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// Frame confidence is the frame ( SNR * consistency )
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confidence = snr * (1.0 - divergence);
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#else
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// Frame confidence is the frame SNR
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confidence = snr;
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#endif
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*ampl_outp = avg_bit_sig;
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