FGFS-4.1/gr-air-modes
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Preamble detector cleanup. Better for >2 samps/symbol.

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This commit is contained in:
Nick Foster 2010-11-19 16:38:32 -08:00
parent 72248eaecf
commit d173f9e256
2 changed files with 27 additions and 42 deletions
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65
src/lib/air_modes_preamble.cc
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@ -85,15 +85,15 @@ int air_modes_preamble::work(int noutput_items,
//the packets are so short we choose not to do any sort of closed-loop synchronization after this simple gating. if we get a good center sample, the drift should be negligible. //the packets are so short we choose not to do any sort of closed-loop synchronization after this simple gating. if we get a good center sample, the drift should be negligible.
pulse_offsets[0] = i; pulse_offsets[0] = 0;
pulse_offsets[1] = i+int(1.0 * d_samples_per_symbol); pulse_offsets[1] = int(1.0 * d_samples_per_symbol);
pulse_offsets[2] = i+int(3.5 * d_samples_per_symbol); pulse_offsets[2] = int(3.5 * d_samples_per_symbol);
pulse_offsets[3] = i+int(4.5 * d_samples_per_symbol); pulse_offsets[3] = int(4.5 * d_samples_per_symbol);
bit_energies[0] = bit_energy(&inraw[pulse_offsets[0]], d_samples_per_chip); bit_energies[0] = bit_energy(&inraw[i+pulse_offsets[0]], d_samples_per_chip);
bit_energies[1] = bit_energy(&inraw[pulse_offsets[1]], d_samples_per_chip); bit_energies[1] = bit_energy(&inraw[i+pulse_offsets[1]], d_samples_per_chip);
bit_energies[2] = bit_energy(&inraw[pulse_offsets[2]], d_samples_per_chip); bit_energies[2] = bit_energy(&inraw[i+pulse_offsets[2]], d_samples_per_chip);
bit_energies[3] = bit_energy(&inraw[pulse_offsets[3]], d_samples_per_chip); bit_energies[3] = bit_energy(&inraw[i+pulse_offsets[3]], d_samples_per_chip);
//search for the rest of the pulses at their expected positions //search for the rest of the pulses at their expected positions
if( bit_energies[1] < pulse_threshold) continue; if( bit_energies[1] < pulse_threshold) continue;
@ -128,40 +128,25 @@ int air_modes_preamble::work(int noutput_items,
//just for kicks, after validating a preamble, you might want to use all four peaks to form a more accurate "average" center sample time, so that if noise corrupts the first leading edge //just for kicks, after validating a preamble, you might want to use all four peaks to form a more accurate "average" center sample time, so that if noise corrupts the first leading edge
//sample, you don't mis-sample the entire packet. //sample, you don't mis-sample the entire packet.
//this could also be done in a separate packet, although it probably saves CPU to do it here //this could also be done in a separate block, although it probably saves CPU to do it here
//for the 2 samples per chip case, you can just add up the peaks at the expected peak times, then do the same for +1, and -1. //for the 2 samples per chip case, you can just add up the peaks at the expected peak times, then do the same for +1.
if(valid_preamble) { if(valid_preamble) {
i--;
do {
i++;
gate_sum_now = bit_energy(&inraw[i+pulse_offsets[0]], d_samples_per_chip)
+ bit_energy(&inraw[i+pulse_offsets[1]], d_samples_per_chip)
+ bit_energy(&inraw[i+pulse_offsets[2]], d_samples_per_chip)
+ bit_energy(&inraw[i+pulse_offsets[3]], d_samples_per_chip);
gate_sum_now = bit_energies[0] + bit_energies[1] + bit_energies[2] + bit_energies[3];
// gate_sum_early = bit_energy(&inraw[pulse_offsets[0]-1], d_samples_per_chip) gate_sum_late = bit_energy(&inraw[i+pulse_offsets[0]+1], d_samples_per_chip)
// + bit_energy(&inraw[pulse_offsets[1]-1], d_samples_per_chip) + bit_energy(&inraw[i+pulse_offsets[1]+1], d_samples_per_chip)
// + bit_energy(&inraw[pulse_offsets[2]-1], d_samples_per_chip) + bit_energy(&inraw[i+pulse_offsets[2]+1], d_samples_per_chip)
// + bit_energy(&inraw[pulse_offsets[3]-1], d_samples_per_chip); + bit_energy(&inraw[i+pulse_offsets[3]+1], d_samples_per_chip);
gate_sum_late = bit_energy(&inraw[pulse_offsets[0]+1], d_samples_per_chip) } while(gate_sum_late > gate_sum_now);
+ bit_energy(&inraw[pulse_offsets[1]+1], d_samples_per_chip)
+ bit_energy(&inraw[pulse_offsets[2]+1], d_samples_per_chip) outattrib[i] = 1;
+ bit_energy(&inraw[pulse_offsets[3]+1], d_samples_per_chip);
/*
if(d_samples_per_chip <= 2) {
gate_sum_now = inraw[pulse_offsets[0]+0] + inraw[pulse_offsets[1]+0] + inraw[pulse_offsets[2]+0] + inraw[pulse_offsets[3]+0];
gate_sum_early = inraw[pulse_offsets[0]-1] + inraw[pulse_offsets[1]-1] + inraw[pulse_offsets[2]-1] + inraw[pulse_offsets[3]-1];
gate_sum_late = inraw[pulse_offsets[0]+1] + inraw[pulse_offsets[1]+1] + inraw[pulse_offsets[2]+1] + inraw[pulse_offsets[3]+1];
} else {
for(int j = 1-d_samples_per_chip/2; j < d_samples_per_chip/2; j++) {
gate_sum_now += inraw[j+pulse_offsets[0]+0] + inraw[j+pulse_offsets[1]+0] + inraw[j+pulse_offsets[2]+0] + inraw[j+pulse_offsets[3]+0];
gate_sum_early += inraw[j+pulse_offsets[0]-1] + inraw[j+pulse_offsets[1]-1] + inraw[j+pulse_offsets[2]-1] + inraw[j+pulse_offsets[3]-1];
gate_sum_late += inraw[j+pulse_offsets[0]+1] + inraw[j+pulse_offsets[1]+1] + inraw[j+pulse_offsets[2]+1] + inraw[j+pulse_offsets[3]+1];
}
}
*/
// if(gate_sum_early > gate_sum_now) { //i think this is redundant
// outattrib[i-1] = 1;
// }
/*else*/ if(gate_sum_late > gate_sum_now) {
outattrib[i+1] = 1;
i+=1; //so we skip the next one and don't overwrite it
}
else outattrib[i] = 1;
} else outattrib[i] = 0; } else outattrib[i] = 0;
} }

2
src/lib/air_modes_slicer.cc
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@ -167,7 +167,7 @@ int air_modes_slicer::work(int noutput_items,
uint64_t timestamp_secs, timestamp_sample, timestamp_delta; uint64_t timestamp_secs, timestamp_sample, timestamp_delta;
double timestamp_frac; double timestamp_frac;
pmt::pmt_t timestamp = pmt::mp(pmt::mp(0), pmt::mp(0)); //so we don't barf if there isn't one pmt::pmt_t timestamp;
get_tags_in_range(tags, 0, abs_sample_cnt, abs_sample_cnt + i, pmt::pmt_string_to_symbol("packet_time_stamp")); get_tags_in_range(tags, 0, abs_sample_cnt, abs_sample_cnt + i, pmt::pmt_string_to_symbol("packet_time_stamp"));
//tags.back() is the most recent timestamp, then. //tags.back() is the most recent timestamp, then.