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Work on the telemetry decoder to support the variable-length correlator in GPS L1 CA tracking

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This commit is contained in:
Javier Arribas
2016-03-17 18:54:41 +01:00
parent 2f61ad7c64
commit 840bb1b9a3
5 changed files with 122 additions and 132 deletions
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197
src/algorithms/telemetry_decoder/gnuradio_blocks/gps_l1_ca_telemetry_decoder_cc.cc
View File

@@ -59,16 +59,16 @@ gps_l1_ca_make_telemetry_decoder_cc(Gnss_Satellite satellite, boost::shared_ptr<
void gps_l1_ca_telemetry_decoder_cc::forecast (int noutput_items, gr_vector_int &ninput_items_required)
{
if (noutput_items != 0)
{
for (unsigned i = 0; i < 3; i++)
{
ninput_items_required[i] = d_samples_per_bit * 8; //set the required sample history
}
}
}
//void gps_l1_ca_telemetry_decoder_cc::forecast (int noutput_items, gr_vector_int &ninput_items_required)
//{
// if (noutput_items != 0)
// {
// for (unsigned i = 0; i < 3; i++)
// {
// ninput_items_required[i] = d_samples_per_bit * 8; //set the required sample history
// }
// }
//}
@@ -181,114 +181,101 @@ int gps_l1_ca_telemetry_decoder_cc::general_work (int noutput_items, gr_vector_i
// ########### Output the tracking data to navigation and PVT ##########
const Gnss_Synchro **in = (const Gnss_Synchro **) &input_items[0]; //Get the input samples pointer
// TODO Optimize me!
if (in[0][d_samples_per_bit*8 - 1].symbol_integration_enabled==false)
// keep the last valid symbols
if (in[0]->Flag_valid_symbol_output==true)
{
//******* preamble correlation ********
for (unsigned int i = 0; i < d_samples_per_bit*8; i++)
d_symbol_history.push_back(in[0]->Prompt_I);
if (static_cast<int>(d_symbol_history.size())>GPS_CA_PREAMBLE_LENGTH_SYMBOLS)
{
if (in[0][i].Prompt_I < 0) // symbols clipping
{
corr_value -= d_preambles_symbols[i];
}
else
{
corr_value += d_preambles_symbols[i];
}
d_symbol_history.pop_front();
}
}else{
//******* preamble correlation ********
for (unsigned int i = 0; i < d_samples_per_bit*8; i++)
{
if (in[0][i].Flag_valid_symbol_output==true)
{
if (in[0][i].Prompt_I < 0) // symbols clipping
if (d_symbol_history.size()==GPS_CA_PREAMBLE_LENGTH_SYMBOLS)
{
//******* preamble correlation ********
int current_symbol_index=0;
for (int i = 0; i < GPS_CA_PREAMBLE_LENGTH_SYMBOLS/in[0]->correlation_length_ms; i++)
{
current_symbol_index=i*in[0]->correlation_length_ms;//+static_cast<int>(floor(in[0]->correlation_length_ms/2));
if (d_symbol_history.at(i) < 0) // symbols clipping
{
corr_value -= d_preambles_symbols[i]*d_samples_per_bit;
//symbol weight expansion using the current tracking correlation length
corr_value -= d_preambles_symbols[current_symbol_index]*in[0]->correlation_length_ms;
}
else
{
corr_value += d_preambles_symbols[i]*d_samples_per_bit;
//symbol weight expansion using the current tracking correlation length
corr_value += d_preambles_symbols[current_symbol_index]*in[0]->correlation_length_ms;
}
}
}
}
}
if (abs(corr_value)>120)
{
std::cout<<abs(corr_value)<<std::endl;
}
}
d_flag_preamble = false;
//******* frame sync ******************
if (abs(corr_value) == 160)
{
//TODO: Rewrite with state machine
if (d_stat == 0)
{
d_GPS_FSM.Event_gps_word_preamble();
d_preamble_index = d_sample_counter;//record the preamble sample stamp
DLOG(INFO) << "Preamble detection for SAT " << this->d_satellite;
d_symbol_accumulator = 0; //sync the symbol to bits integrator
d_symbol_accumulator_counter = 0;
d_frame_bit_index = 7;
d_stat = 1; // enter into frame pre-detection status
}
else if (d_stat == 1) //check 6 seconds of preamble separation
{
preamble_diff = d_sample_counter - d_preamble_index;
if (abs(preamble_diff - 6000) < 1)
{
d_GPS_FSM.Event_gps_word_preamble();
d_flag_preamble = true;
d_preamble_index = d_sample_counter; //record the preamble sample stamp (t_P)
d_preamble_time_seconds = in[0][0].Tracking_timestamp_secs;// - d_preamble_duration_seconds; //record the PRN start sample index associated to the preamble
d_frame_bit_index = 7;
if (!d_flag_frame_sync)
{
//send asynchronous message to tracking to inform of frame sync and extend correlation time
pmt::pmt_t value = pmt::from_long(d_preamble_index-1);
this->message_port_pub(pmt::mp("preamble_index"),value);
if (abs(corr_value) == GPS_CA_PREAMBLE_LENGTH_SYMBOLS)
{
if (d_stat == 0)
{
d_GPS_FSM.Event_gps_word_preamble();
d_preamble_index = d_sample_counter;//record the preamble sample stamp
std::cout << "Preamble detection for SAT " << this->d_satellite;
d_symbol_accumulator = 0; //sync the symbol to bits integrator
d_symbol_accumulator_counter = 0;
d_frame_bit_index = 7;
d_stat = 1; // enter into frame pre-detection status
}
else if (d_stat == 1) //check 6 seconds of preamble separation
{
preamble_diff = d_sample_counter - d_preamble_index;
if (abs(preamble_diff - 6000) < 1)
{
std::cout <<"preamble! corr lenght="<<in[0]->correlation_length_ms<<std::endl;
d_GPS_FSM.Event_gps_word_preamble();
d_flag_preamble = true;
d_preamble_index = d_sample_counter; //record the preamble sample stamp (t_P)
d_preamble_time_seconds = in[0][0].Tracking_timestamp_secs;// - d_preamble_duration_seconds; //record the PRN start sample index associated to the preamble
d_frame_bit_index = 7;
if (!d_flag_frame_sync)
{
//send asynchronous message to tracking to inform of frame sync and extend correlation time
pmt::pmt_t value = pmt::from_long(d_preamble_index-2);
this->message_port_pub(pmt::mp("preamble_index"),value);
d_flag_frame_sync = true;
if (corr_value < 0)
{
flag_PLL_180_deg_phase_locked = true; //PLL is locked to opposite phase!
DLOG(INFO) << " PLL in opposite phase for Sat "<< this->d_satellite.get_PRN();
}
else
{
flag_PLL_180_deg_phase_locked = false;
}
DLOG(INFO) << " Frame sync SAT " << this->d_satellite << " with preamble start at " << d_preamble_time_seconds << " [s]";
}
}
}
}
else
{
if (d_stat == 1)
{
preamble_diff = d_sample_counter - d_preamble_index;
if (preamble_diff > 6001)
{
DLOG(INFO) << "Lost of frame sync SAT " << this->d_satellite << " preamble_diff= " << preamble_diff;
d_stat = 0; //lost of frame sync
d_flag_frame_sync = false;
flag_TOW_set = false;
}
}
}
d_flag_frame_sync = true;
if (corr_value < 0)
{
flag_PLL_180_deg_phase_locked = true; //PLL is locked to opposite phase!
std::cout << " PLL in opposite phase for Sat "<< this->d_satellite.get_PRN();
}
else
{
flag_PLL_180_deg_phase_locked = false;
}
std::cout << " Frame sync SAT " << this->d_satellite << " with preamble start at " << d_preamble_time_seconds << " [s]";
}
}else{
if (preamble_diff > 6001)
{
std::cout << "Lost of frame sync SAT " << this->d_satellite << " preamble_diff= " << preamble_diff;
d_stat = 0; //lost of frame sync
d_flag_frame_sync = false;
flag_TOW_set = false;
}
}
}
}
//******* SYMBOL TO BIT *******
if (in[0][d_samples_per_bit*8 - 1].Flag_valid_symbol_output==true)
if (in[0]->Flag_valid_symbol_output==true)
{
if (in[0][d_samples_per_bit*8 - 1].symbol_integration_enabled==true)
{
// extended correlation to bit period is enabled in tracking!
// 1 symbol = 1 bit
d_symbol_accumulator = in[0][d_samples_per_bit*8 - 1].Prompt_I; // accumulate the input value in d_symbol_accumulator
d_symbol_accumulator_counter=20;
}else{
// 20 symbols = 1 bit: do symbols integration in telemetry decoder
d_symbol_accumulator += in[0][d_samples_per_bit*8 - 1].Prompt_I; // accumulate the input value in d_symbol_accumulator
d_symbol_accumulator_counter++;
}
// extended correlation to bit period is enabled in tracking!
d_symbol_accumulator += in[0]->Prompt_I; // accumulate the input value in d_symbol_accumulator
d_symbol_accumulator_counter+=in[0]->correlation_length_ms;
}
if (d_symbol_accumulator_counter == 20 )
@@ -342,8 +329,6 @@ int gps_l1_ca_telemetry_decoder_cc::general_work (int noutput_items, gr_vector_i
{
d_GPS_frame_4bytes <<= 1; //shift 1 bit left the telemetry word
}
}
// output the frame
consume_each(1); //one by one
@@ -381,8 +366,8 @@ int gps_l1_ca_telemetry_decoder_cc::general_work (int noutput_items, gr_vector_i
if (flag_PLL_180_deg_phase_locked == true)
{
//correct the accumulated phase for the costas loop phase shift, if required
current_synchro_data.Carrier_phase_rads += GPS_PI;
//correct the accumulated phase for the costas loop phase shift, if required
current_synchro_data.Carrier_phase_rads += GPS_PI;
}
if(d_dump == true)

7
src/algorithms/telemetry_decoder/gnuradio_blocks/gps_l1_ca_telemetry_decoder_cc.h
View File

@@ -85,7 +85,7 @@ public:
* \brief Function which tells the scheduler how many input items
* are required to produce noutput_items output items.
*/
void forecast (int noutput_items, gr_vector_int &ninput_items_required);
//void forecast (int noutput_items, gr_vector_int &ninput_items_required);
private:
friend gps_l1_ca_telemetry_decoder_cc_sptr
@@ -107,6 +107,7 @@ private:
bool d_flag_frame_sync;
// symbols
std::deque<double> d_symbol_history;
double d_symbol_accumulator;
short int d_symbol_accumulator_counter;
@@ -138,10 +139,6 @@ private:
double d_TOW_at_Preamble;
double d_TOW_at_current_symbol;
std::deque<double> d_symbol_TOW_queue_s;
// Doppler and Phase accumulator queue for interpolation in Observables
std::deque<double> d_carrier_doppler_queue_hz;
std::deque<double> d_acc_carrier_phase_queue_rads;
double Prn_timestamp_at_preamble_ms;
bool flag_TOW_set;