FGFS-4.1/gr-air-modes
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fix crap, use confidence

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This commit is contained in:
Nick Foster 2011-06-11 21:40:51 -07:00
parent 8b1c1791c7
commit 28366627c5
3 changed files with 29 additions and 25 deletions
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47
src/lib/air_modes_slicer.cc
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@ -70,8 +70,8 @@ static bool pmtcompare(pmt::pmt_t x, pmt::pmt_t y)
//this slicer is courtesy of Lincoln Labs. supposedly it is more resistant to mode A/C FRUIT. //this slicer is courtesy of Lincoln Labs. supposedly it is more resistant to mode A/C FRUIT.
//see http://adsb.tc.faa.gov/WG3_Meetings/Meeting8/Squitter-Lon.pdf //see http://adsb.tc.faa.gov/WG3_Meetings/Meeting8/Squitter-Lon.pdf
static bool slicer(const float bit0, const float bit1, const float ref) { static slice_result_t slicer(const float bit0, const float bit1, const float ref) {
bool slice, confidence; slice_result_t result;
//3dB limits for bit slicing and confidence measurement //3dB limits for bit slicing and confidence measurement
float highlimit=ref*2; float highlimit=ref*2;
@ -81,28 +81,28 @@ static bool slicer(const float bit0, const float bit1, const float ref) {
bool secondchip_inref = ((bit1 > lowlimit) && (bit1 < highlimit)); bool secondchip_inref = ((bit1 > lowlimit) && (bit1 < highlimit));
if(firstchip_inref && !secondchip_inref) { if(firstchip_inref && !secondchip_inref) {
slice = 1; result.decision = 1;
confidence = 1; result.confidence = 1;
} }
else if(secondchip_inref && !firstchip_inref) { else if(secondchip_inref && !firstchip_inref) {
slice = 0; result.decision = 0;
confidence = 1; result.confidence = 1;
} }
else if(firstchip_inref && secondchip_inref) { else if(firstchip_inref && secondchip_inref) {
slice = bit0 > bit1; result.decision = bit0 > bit1;
confidence = 0; 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) { //in this case, we determine the bit by whichever is larger, and we determine high confidence if the low chip is 6dB below reference.
slice = bit0 > bit1; result.decision = bit0 > bit1;
if(slice) { if(result.decision) {
if(bit1 < lowlimit * 0.5) confidence = 1; if(bit1 < lowlimit * 0.5) result.confidence = 1;
else confidence = 0; else result.confidence = 0;
} else { } else {
if(bit0 < lowlimit * 0.5) confidence = 1; if(bit0 < lowlimit * 0.5) result.confidence = 1;
else confidence = 0; else result.confidence = 0;
} }
} }
return slice; return result;
} }
/* /*
@ -155,10 +155,9 @@ int air_modes_slicer::work(int noutput_items,
//now let's slice the header so we can determine if it's a short pkt or a long pkt //now let's slice the header so we can determine if it's a short pkt or a long pkt
unsigned char pkt_hdr = 0; unsigned char pkt_hdr = 0;
for(int j=0; j < 5; j++) { for(int j=0; j < 5; j++) {
bool slice = slicer(in[i+j*2], in[i+j*2+1], rx_packet.reference_level); slice_result_t slice_result = slicer(in[i+j*2], in[i+j*2+1], rx_packet.reference_level);
if(slice) pkt_hdr += 1 << (4-j); if(slice_result.decision) pkt_hdr += 1 << (4-j);
} }
//std::cout << "SLICER: TYPE " << int(pkt_hdr) << std::endl;
if(pkt_hdr == 17) rx_packet.type = Long_Packet; if(pkt_hdr == 17) rx_packet.type = Long_Packet;
else rx_packet.type = Short_Packet; else rx_packet.type = Short_Packet;
@ -169,18 +168,18 @@ int air_modes_slicer::work(int noutput_items,
//it's slice time! //it's slice time!
//TODO: don't repeat your work here, you already have the first 5 bits //TODO: don't repeat your work here, you already have the first 5 bits
for(int j = 0; j < packet_length; j++) { for(int j = 0; j < packet_length; j++) {
bool slice = slicer(in[i+j*2], in[i+j*2+1], rx_packet.reference_level); slice_result_t slice_result = slicer(in[i+j*2], in[i+j*2+1], rx_packet.reference_level);
//put the data into the packet //put the data into the packet
if(slice) { if(slice_result.decision) {
rx_packet.data[j/8] += 1 << (7-(j%8)); rx_packet.data[j/8] += 1 << (7-(j%8));
} }
//put the confidence decision into the packet //put the confidence decision into the packet
// if(confidence) { if(slice_result.confidence) {
//rx_packet.confidence[j/8] += 1 << (7-(j%8)); //rx_packet.confidence[j/8] += 1 << (7-(j%8));
// } else { } else {
// if(rx_packet.numlowconf < 24) rx_packet.lowconfbits[rx_packet.numlowconf++] = j; if(rx_packet.numlowconf < 24) rx_packet.lowconfbits[rx_packet.numlowconf++] = j;
// } }
} }
/******************** BEGIN TIMESTAMP BS ******************/ /******************** BEGIN TIMESTAMP BS ******************/

5
src/lib/air_modes_types.h
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@ -39,4 +39,9 @@ struct modes_packet {
double timestamp; double timestamp;
}; };
struct slice_result_t {
bool decision;
bool confidence;
};
#endif #endif

2
src/python/uhd_modes.py
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@ -95,7 +95,7 @@ class adsb_rx_block (gr.top_block):
#self.lpfiltcoeffs = gr.firdes.low_pass(1, rate, 1.8e6, 200e3) #self.lpfiltcoeffs = gr.firdes.low_pass(1, rate, 1.8e6, 200e3)
#self.lpfilter = gr.fir_filter_fff(1, self.lpfiltcoeffs) #self.lpfilter = gr.fir_filter_fff(1, self.lpfiltcoeffs)
self.filter = gr.fir_filter_fff(1, self.filtcoeffs) #self.filter = gr.fir_filter_fff(1, self.filtcoeffs)
#rate = int(2e6) #rate = int(2e6)
self.preamble = air.modes_preamble(rate, options.threshold) self.preamble = air.modes_preamble(rate, options.threshold)