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Some work on the mlat stuff, and restoring sanity to the gr-uhd tags interface

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This commit is contained in:
Nick Foster
2011-09-07 15:49:14 -07:00
parent e1c6c467a4
commit f3957194f5
2 changed files with 42 additions and 18 deletions
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18
src/lib/air_modes_preamble.cc
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@@ -80,14 +80,15 @@ static double correlate_preamble(const float *in, int samples_per_chip) {
static double pmt_to_timestamp(pmt::pmt_t tstamp, uint64_t abs_sample_cnt, double secs_per_sample) {
uint64_t ts_sample, ticks;
uint64_t ts_sample;
double last_stamp;
if(pmt::pmt_symbol_to_string(gr_tags::get_key(tstamp)) != "timestamp") return 0;
ticks = pmt_to_uint64(gr_tags::get_value(tstamp));
last_stamp = pmt_to_double(gr_tags::get_value(tstamp));
ts_sample = gr_tags::get_nitems(tstamp);
//std::cout << "HEY WE GOT A STAMP AT " << ticks << " TICKS AT SAMPLE " << ts_sample << " ABS SAMPLE CNT IS " << abs_sample_cnt << std::endl;
return double(ticks+abs_sample_cnt) * secs_per_sample;
return double(abs_sample_cnt * secs_per_sample) + last_stamp;
}
int air_modes_preamble::general_work(int noutput_items,
@@ -114,7 +115,7 @@ int air_modes_preamble::general_work(int noutput_items,
if(tstamp_tags.size() > 0) {
d_timestamp = tstamp_tags.back();
}
for(int i=0; i < ninputs; i++) {
float pulse_threshold = inavg[i] * d_threshold;
if(in[i] > pulse_threshold) { //hey we got a candidate
@@ -125,15 +126,18 @@ int air_modes_preamble::general_work(int noutput_items,
if( in[i+pulse_offsets[3]] < pulse_threshold ) continue;
//get a more accurate bit center by finding the correlation peak across all four preamble bits
bool late = false;
bool late, early;
do {
double now_corr = correlate_preamble(in+i, d_samples_per_chip);
double late_corr = correlate_preamble(in+i+1, d_samples_per_chip);
double early_corr = correlate_preamble(in+i-1, d_samples_per_chip);
late = (late_corr > now_corr);
//early = (early_corr > now_corr);
if(late) i++;
} while(late);
//if(early && i>0) { std::cout << "EARLY " << i << std::endl; i--; }
} while(late);// xor early);
//now check to see that the rest of the chips in the preamble
//now check to see that the non-peak symbols in the preamble
//are below the peaks by threshold dB
float avgpeak = ( in[i+pulse_offsets[0]]
+ in[i+pulse_offsets[1]]

42
src/python/get_correlated_records.py
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@@ -79,16 +79,36 @@ for msg in position_reports:
offset_list.append({"aircraft": data["shortdata"], "times": rel_times})
#this is a list of unique aircraft, heard by all stations, which transmitted position packets
#we do drift calcs separately for each aircraft in the set because mixing them seems to screw things up
#i haven't really sat down and figured out why that is yet
unique_aircraft = list(set([x["aircraft"] for x in offset_list]))
#todo: the below can be done cleaner with nested list comprehensions
for ac in unique_aircraft:
for i in range(1,len(stations)):
#pull out a list of unique aircraft from the offset list
rel_times_for_one_ac = [report["times"][i]-report["times"][0] for report in offset_list if report["aircraft"] == ac]
abs_times_for_one_ac = [report["times"][0] for report in offset_list if report["aircraft"] == ac]
#find drift error
drift_error = [(y-x)/(b-a) for x,y,a,b in zip(rel_times_for_one_ac, rel_times_for_one_ac[1:], abs_times_for_one_ac, abs_times_for_one_ac[1:])]
drift_error_limited = [x for x in drift_error if abs(x) < 1e-5]
print "drift from %d relative to station 0 for ac %x: %.3fppm" % (i, ac & 0xFFFFFF, numpy.mean(drift_error_limited) * 1e6)
#get a list of reported times gathered by the unique aircraft that transmitted them
#abs_unique_times = [report["times"] for ac in unique_aircraft for report in offset_list if report["aircraft"] == ac]
#print abs_unique_times
#todo: the below can be done cleaner with nested list comprehensions
clock_rate_corrections = [0]
for i in range(1,len(stations)):
drift_error_limited = []
for ac in unique_aircraft:
times = [report["times"] for report in offset_list if report["aircraft"] == ac]
s0_times = [report[0] for report in times]
rel_times = [report[i]-report[0] for report in times]
#find drift error rate
drift_error = [(y-x)/(b-a) for x,y,a,b in zip(rel_times, rel_times[1:], s0_times[0:], s0_times[1:])]
drift_error_limited.append([x for x in drift_error if abs(x) < 1e-5])
#flatten the list of lists (tacky, there's a better way)
drift_error_limited = [x for sublist in drift_error_limited for x in sublist]
clock_rate_corrections.append(0-numpy.mean(drift_error_limited))
for i in range(len(clock_rate_corrections)):
print "drift from %d relative to station 0: %.3fppm" % (i, clock_rate_corrections[i] * 1e6)
#ok now we have clock rate corrections for each station, and we can multilaterate like hell
#we'll need a way to get a clock offset at a particular time, in case the dataset has a discontinuity
#actually we don't, unless we still have the old "timestamps-are-wrong-in-b100" issue
#remember to subtract out rel_time before correcting for clock rate error
#start with all_heard