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minimodem: refine frame position if confidence falls 

Allows for more accurate tracking, esp. for no-frame-bits protocols.
Fixes tests/test-80-SAME-datastream.
This commit is contained in:
Kamal Mostafa 2012-11-03 14:16:23 -07:00
parent 4709b5d146
commit 032d0bb79c
1 changed files with 37 additions and 20 deletions
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57
src/minimodem.c
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@ -840,6 +840,7 @@ main( int argc, char*argv[] )
unsigned int frame_nsamples = nsamples_per_bit * frame_n_bits + 0.5;
float track_amplitude = 0.0;
float peak_confidence = 0.0;
signal(SIGINT, rx_stop_sighandler);
@ -986,11 +987,11 @@ main( int argc, char*argv[] )
try_max_nsamples = nsamples_per_bit;
try_max_nsamples += nsamples_overscan;
// FSK_ANALYZE_NSTEPS Try 4 frame positions across the try_max_nsamples
// FSK_ANALYZE_NSTEPS Try 3 frame positions across the try_max_nsamples
// range. Using a larger nsteps allows for more accurate tracking of
// fast/slow signals (at decreased performance). Note also
// FSK_ANALYZE_NSTEPS_CARRIER_LOCK below, which refines the frame
// position upon first acquiring carrier.
// FSK_ANALYZE_NSTEPS_FINE below, which refines the frame
// position upon first acquiring carrier, or if confidence falls.
#define FSK_ANALYZE_NSTEPS 3
unsigned int try_step_nsamples = try_max_nsamples / FSK_ANALYZE_NSTEPS;
if ( try_step_nsamples == 0 )
@ -1019,14 +1020,18 @@ main( int argc, char*argv[] )
&frame_start_sample
);
int do_refine_frame = 0;
if ( confidence < peak_confidence * 0.75 ) {
do_refine_frame = 1;
debug_log(" ... do_refine_frame rescan (confidence %.3f << %.3f peak)\n", confidence, peak_confidence);
peak_confidence = 0;
}
// no-confidence if amplitude drops abruptly to < 25% of the
// track_amplitude, which follows amplitude with hysteresis
if ( amplitude < track_amplitude * 0.25 ) {
confidence = 0;
} else {
track_amplitude = ( track_amplitude + amplitude ) / 2;
debug_log("@ confidence=%.3f amplitude=%.3f track_amplitude=%.3f\n",
confidence, amplitude, track_amplitude );
}
#define FSK_MAX_NOCONFIDENCE_BITS 20
@ -1086,14 +1091,26 @@ main( int argc, char*argv[] )
fskp->b_mark * fskp->band_width);
}
if ( !quiet_mode )
fprintf(stderr, "###\n");
carrier = 1;
bfsk_databits_decode(0, 0, 0, 0); // reset the frame processor
do_refine_frame = 1;
debug_log(" ... do_refine_frame rescan (acquired carrier)\n");
}
if ( do_refine_frame )
{
if ( confidence < INFINITY && try_step_nsamples > 1 ) {
// FSK_ANALYZE_NSTEPS_CARRIER_LOCK:
// Scan again, but try harder to find the best frame upon
// acquiring carrier. Since we found a valid confidence frame
// in the "sloppy" fsk_find_frame() call already, we're sure
// to find one at least as good this time.
#define FSK_ANALYZE_NSTEPS_CARRIER_LOCK 8
try_step_nsamples = try_max_nsamples / FSK_ANALYZE_NSTEPS_CARRIER_LOCK;
// FSK_ANALYZE_NSTEPS_FINE:
// Scan again, but try harder to find the best frame.
// Since we found a valid confidence frame in the "sloppy"
// fsk_find_frame() call already, we're sure to find one at
// least as good this time.
#define FSK_ANALYZE_NSTEPS_FINE 8
try_step_nsamples = try_max_nsamples / FSK_ANALYZE_NSTEPS_FINE;
if ( try_step_nsamples == 0 )
try_step_nsamples = 1;
try_confidence_search_limit = INFINITY;
@ -1116,14 +1133,14 @@ main( int argc, char*argv[] )
frame_start_sample = frame_start_sample2;
}
}
if ( !quiet_mode )
fprintf(stderr, "###\n");
carrier = 1;
bfsk_databits_decode(0, 0, 0, 0); // reset the frame processor
}
track_amplitude = ( track_amplitude + amplitude ) / 2;
if ( peak_confidence < confidence )
peak_confidence = confidence;
debug_log("@ confidence=%.3f peak_conf=%.3f amplitude=%.3f track_amplitude=%.3f\n",
confidence, peak_confidence, amplitude, track_amplitude );
confidence_total += confidence;
amplitude_total += amplitude;
nframes_decoded++;