FGFS-4.1/gr-air-modes
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Preamble was sometimes consuming more samples than it was given, due to rounding issues and due to the early/late gate peak detector.

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This commit is contained in:
Nick Foster 2012-09-14 09:41:21 -07:00
parent d1b69405bf
commit 8939a72e62
1 changed files with 15 additions and 5 deletions
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20
lib/air_modes_preamble.cc
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@ -53,7 +53,7 @@ air_modes_preamble::air_modes_preamble(int channel_rate, float threshold_db) :
str << name() << unique_id();
d_me = pmt::pmt_string_to_symbol(str.str());
d_key = pmt::pmt_string_to_symbol("preamble_found");
set_history(d_check_width);
set_history(d_samples_per_symbol);
}
static void integrate_and_dump(float *out, const float *in, int chips, int samps_per_chip) {
@ -101,7 +101,13 @@ int air_modes_preamble::general_work(int noutput_items,
{
const float *in = (const float *) input_items[0];
const float *inavg = (const float *) input_items[1];
const int ninputs = std::min(ninput_items[0], ninput_items[1]); //just in case
int mininputs = std::min(ninput_items[0], ninput_items[1]); //they should be matched but let's be safe
//round number of input samples down to nearest d_samples_per_chip
//we also subtract off d_samples_per_chip to allow the bit center finder some leeway
const int ninputs = std::max(mininputs - (mininputs % d_samples_per_chip) - d_samples_per_chip, 0);
if (ninputs <= 0) { consume_each(0); return 0; }
float *out = (float *) output_items[0];
if(0) std::cout << "Preamble called with " << ninputs << " samples" << std::endl;
@ -132,15 +138,18 @@ int air_modes_preamble::general_work(int noutput_items,
//get a more accurate bit center by finding the correlation peak across all four preamble bits
bool late, early;
int how_late = 0;
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++;
if(late) { i++; how_late++; }
//if(early && i>0) { std::cout << "EARLY " << i << std::endl; i--; }
} while(late);// xor early);
} while(late and how_late < d_samples_per_chip);// xor early);
if(0) std::cout << "We were " << how_late << " samples late" << std::endl;
//now check to see that the non-peak symbols in the preamble
//are below the peaks by threshold dB
@ -160,6 +169,7 @@ int air_modes_preamble::general_work(int noutput_items,
//be sure we've got enough room in the input buffer to copy out a whole packet
if(ninputs-i < 240*d_samples_per_chip) {
consume_each(std::max(i-1,0));
if(0) std::cout << "Preamble consumed " << std::max(i-1,0) << ", returned 0 (no room)" << std::endl;
return 0;
}
@ -190,7 +200,7 @@ int air_modes_preamble::general_work(int noutput_items,
//std::cout << "PREAMBLE" << std::endl;
//produce only one output per work call -- TODO this should probably change
if(0) std::cout << "Preamble consumed " << i+240*d_samples_per_chip << ", returned 240" << std::endl;
if(0) std::cout << "Preamble consumed " << i+240*d_samples_per_chip << "with i=" << i << ", returned 240" << std::endl;
consume_each(i+240*d_samples_per_chip);
return 240;
}