FGFS-4.1/gr-air-modes
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interim commit with some debug stuff thrown in.

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This commit is contained in:
Nick Foster 2011-06-12 00:56:22 -07:00
parent ba7a6085cb
commit 87444eb980
2 changed files with 19 additions and 42 deletions
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14
src/lib/air_modes_preamble.cc
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@ -137,12 +137,12 @@ int air_modes_preamble::general_work(int noutput_items,
//all right i'm prepared to call this a preamble
//let's integrate and dump the output
i -= d_samples_per_chip-1;
integrate_and_dump(out, &in[i], 240, d_samples_per_chip);
// out[0] = 1.0; //for debug
// out[1] = out[2] = out[3] = out[4] = avgpeak;
// out[5] = out[6] = out[7] = out[8] = space_threshold;
// out[9] = 0.0;
//FIXME: disable and use center sample
for(int j=0; j<240; j++) {
out[j] = in[i+j*d_samples_per_chip];
}
//i -= d_samples_per_chip-1;
//integrate_and_dump(out, &in[i], 240, d_samples_per_chip);
//now tag the preamble
add_item_tag(0, //stream ID
@ -154,8 +154,6 @@ int air_modes_preamble::general_work(int noutput_items,
//std::cout << "PREAMBLE" << std::endl;
//produce only one output per work call
//we consume a short packet length, while generating a long one
//that way we don't miss two short pkts in the span of one long one
consume_each(i+240*d_samples_per_chip);
return 240;
}

47
src/lib/air_modes_slicer.cc
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@ -93,7 +93,7 @@ static slice_result_t slicer(const float bit0, const float bit1, const float ref
result.decision = bit0 > bit1;
result.confidence = 0;
}
else if(!firstchip_inref && !secondchip_inref) { //in this case, we determine the bit by whichever is larger, and we determine high confidence if the low chip is 6dB below reference.
else {//if(!firstchip_inref && !secondchip_inref) {
result.decision = bit0 > bit1;
if(result.decision) {
if(bit1 < lowlimit * 0.5) result.confidence = 1;
@ -129,6 +129,7 @@ int air_modes_slicer::work(int noutput_items,
int size = noutput_items - d_check_width; //since it's a sync block, i assume that it runs with ninput_items = noutput_items
int i;
static int n_ok=0, n_badcrc=0, n_loconf=0, n_zeroes=0;
std::vector<pmt::pmt_t> tags;
uint64_t abs_sample_cnt = nitems_read(0);
@ -207,46 +208,22 @@ int air_modes_slicer::work(int noutput_items,
for(int m = 0; m < 14; m++) {
if(rx_packet.data[m]) zeroes = 0;
}
if(zeroes) continue; //toss it
if(zeroes) {n_zeroes++; continue;} //toss it
rx_packet.message_type = (rx_packet.data[0] >> 3) & 0x1F; //get the message type for the parser to conveniently use, and to make decisions on ECC methods
//we note that short packets other than type 11 CANNOT be reliably decoded, since the a/c address is encoded with the parity bits.
//mode S in production ATC use relies on the fact that these short packets are reply squitters to transponder requests,
//and so the radar should already know the expected a/c reply address. so, error-correction makes no sense on short packets (other than type 11)
//this means two things: first, we will DROP short packets (other than type 11) with ANY low-confidence bits, since we can't be confident that we're seeing real data
//second, we will only perform error correction on LONG type S packets.
//the limitation on short packets means in practice a short packet has to be at least 6dB above the noise floor in order to be output. long packets can theoretically
//be decoded at the 3dB SNR point. below that and the preamble detector won't fire.
//in practice, this limitation causes you to see a HUGE number of type 11 packets which pass CRC through random luck.
//these packets necessarily have large numbers of low-confidence bits, so we toss them with an arbitrary limit of 10.
//that's a pretty dang low threshold so i don't think we'll drop many legit packets
if(rx_packet.type == Short_Packet && rx_packet.message_type != 11 && rx_packet.numlowconf != 0) continue;
if(rx_packet.message_type == 11 && rx_packet.numlowconf >= 10) continue;
if(rx_packet.type == Short_Packet && rx_packet.message_type != 11 && rx_packet.numlowconf > 2) {n_loconf++; continue;}
if(rx_packet.message_type == 11 && rx_packet.numlowconf >= 10) {n_loconf++; continue;}
//if(rx_packet.numlowconf >= 24) continue; //don't even try, this is the maximum number of errors ECC could possibly correct
//the above line should be part of ECC, and only checked if the message has parity errors
rx_packet.parity = modes_check_parity(rx_packet.data, packet_length);
if(rx_packet.parity && rx_packet.type == Long_Packet) {
bruteResultTypeDef bruteResult = modes_ec_brute(rx_packet);
//parity for packets that aren't type 11 or type 17 is encoded with the transponder ID, which we don't know
//therefore we toss 'em if there's syndrome
//parity for the other short packets is usually nonzero, so they can't really be trusted that far
if(rx_packet.parity && (rx_packet.message_type == 11 || rx_packet.message_type == 17)) {n_badcrc++; continue;}
if(bruteResult == No_Solution) {
continue;
} else if(bruteResult == Multiple_Solutions) {
continue;
} else if(bruteResult == Too_Many_LCBs) {
continue;
} else if(bruteResult == No_Error) {
} else if(bruteResult == Solution_Found) {
// printf("Solution found for %i LCBs!\n", rx_packet.numlowconf);
}
}
//we no longer attempt to brute force error correct via syndrome. it really only gets you 1% additional returns,
//at the expense of a lot of CPU time and complexity
//we'll replicate some data by sending the message type as the first field, followed by the first 8+24=32 bits of the packet, followed by
//56 long packet data bits if applicable (zero-padded if not), followed by parity
@ -279,6 +256,8 @@ int air_modes_slicer::work(int noutput_items,
<< " " << std::setprecision(10) << std::setw(10) << rx_packet.timestamp;
gr_message_sptr msg = gr_make_message_from_string(std::string(d_payload.str()));
d_queue->handle(msg);
n_ok++;
std::cout << "n_ok: " << n_ok << " n_loconf: " << n_loconf << " n_badcrc: " << n_badcrc << " n_zeroes: " << n_zeroes << std::endl;
}