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Improving bit synchronization in GPS L1 CA tracking

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This commit is contained in:
Javier Arribas 2018-07-13 15:23:20 +02:00
parent b779f5cb3d
commit a392117c0b
2 changed files with 98 additions and 20 deletions
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109
src/algorithms/tracking/gnuradio_blocks/dll_pll_veml_tracking.cc
View File

@ -2,6 +2,7 @@
* \file dll_pll_veml_tracking.cc
* \brief Implementation of a code DLL + carrier PLL tracking block.
* \author Antonio Ramos, 2018 antonio.ramosdet(at)gmail.com
* Javier Arribas, 2018. jarribas(at)cttc.es
*
* Code DLL + carrier PLL according to the algorithms described in:
* [1] K.Borre, D.M.Akos, N.Bertelsen, P.Rinder, and S.H.Jensen,
@ -84,10 +85,12 @@ dll_pll_veml_tracking::dll_pll_veml_tracking(const Dll_Pll_Conf &conf_) : gr::bl
this->message_port_register_out(pmt::mp("events"));
this->set_relative_rate(1.0 / static_cast<double>(trk_parameters.vector_length));
// Telemetry bit synchronization message port input (mainly for GPS L1 CA)
this->message_port_register_in(pmt::mp("preamble_samplestamp"));
// initialize internal vars
d_veml = false;
d_cloop = true;
d_synchonizing = false;
d_code_chip_rate = 0.0;
d_secondary_code_length = 0;
d_secondary_code_string = nullptr;
@ -120,6 +123,30 @@ dll_pll_veml_tracking::dll_pll_veml_tracking(const Dll_Pll_Conf &conf_) : gr::bl
d_secondary = false;
trk_parameters.track_pilot = false;
interchange_iq = false;
// set the preamble
unsigned short int preambles_bits[GPS_CA_PREAMBLE_LENGTH_BITS] = GPS_PREAMBLE;
// preamble bits to sampled symbols
d_gps_l1ca_preambles_symbols = static_cast<int *>(volk_gnsssdr_malloc(GPS_CA_PREAMBLE_LENGTH_SYMBOLS * sizeof(int), volk_gnsssdr_get_alignment()));
int n = 0;
for (int i = 0; i < GPS_CA_PREAMBLE_LENGTH_BITS; i++)
{
for (unsigned int j = 0; j < GPS_CA_TELEMETRY_SYMBOLS_PER_BIT; j++)
{
if (preambles_bits[i] == 1)
{
d_gps_l1ca_preambles_symbols[n] = 1;
}
else
{
d_gps_l1ca_preambles_symbols[n] = -1;
}
n++;
}
}
d_symbol_history.resize(GPS_CA_PREAMBLE_LENGTH_SYMBOLS); // Change fixed buffer size
d_symbol_history.clear(); // Clear all the elements in the buffer
}
else if (signal_type.compare("2S") == 0)
{
@ -521,7 +548,6 @@ void dll_pll_veml_tracking::start_tracking()
// enable tracking pull-in
d_state = 1;
d_synchonizing = false;
d_cloop = true;
d_Prompt_buffer_deque.clear();
d_last_prompt = gr_complex(0.0, 0.0);
@ -533,6 +559,11 @@ void dll_pll_veml_tracking::start_tracking()
dll_pll_veml_tracking::~dll_pll_veml_tracking()
{
if (signal_type.compare("1C") == 0)
{
volk_gnsssdr_free(d_gps_l1ca_preambles_symbols);
}
if (d_dump_file.is_open())
{
try
@ -1281,39 +1312,82 @@ int dll_pll_veml_tracking::general_work(int noutput_items __attribute__((unused)
}
else if (d_symbols_per_bit > 1) //Signal does not have secondary code. Search a bit transition by sign change
{
if (d_synchonizing)
float current_tracking_time_s = static_cast<float>(d_sample_counter - d_acq_sample_stamp) / trk_parameters.fs_in;
if (current_tracking_time_s > 10)
{
if (d_Prompt->real() * d_last_prompt.real() > 0.0)
d_symbol_history.push_back(d_Prompt->real());
//******* preamble correlation ********
int corr_value = 0;
if ((d_symbol_history.size() == GPS_CA_PREAMBLE_LENGTH_SYMBOLS)) // and (d_make_correlation or !d_flag_frame_sync))
{
d_current_symbol++;
}
else if (d_current_symbol > d_symbols_per_bit)
for (unsigned int i = 0; i < GPS_CA_PREAMBLE_LENGTH_SYMBOLS; i++)
{
d_synchonizing = false;
d_current_symbol = 1;
if (d_symbol_history.at(i) < 0) // symbols clipping
{
corr_value -= d_gps_l1ca_preambles_symbols[i];
}
else
{
d_current_symbol = 1;
d_last_prompt = *d_Prompt;
corr_value += d_gps_l1ca_preambles_symbols[i];
}
}
else if (d_last_prompt.real() != 0.0)
}
if (corr_value == GPS_CA_PREAMBLE_LENGTH_SYMBOLS)
{
d_current_symbol++;
if (d_current_symbol == d_symbols_per_bit) next_state = true;
//std::cout << "Preamble detected at tracking!" << std::endl;
next_state = true;
}
else
{
d_last_prompt = *d_Prompt;
d_synchonizing = true;
d_current_symbol = 1;
next_state = false;
}
}
else
{
next_state = false;
}
}
else
{
next_state = true;
}
// ########### Output the tracking results to Telemetry block ##########
if (interchange_iq)
{
if (trk_parameters.track_pilot)
{
// Note that data and pilot components are in quadrature. I and Q are interchanged
current_synchro_data.Prompt_I = static_cast<double>((*d_Prompt_Data).imag());
current_synchro_data.Prompt_Q = static_cast<double>((*d_Prompt_Data).real());
}
else
{
current_synchro_data.Prompt_I = static_cast<double>((*d_Prompt).imag());
current_synchro_data.Prompt_Q = static_cast<double>((*d_Prompt).real());
}
}
else
{
if (trk_parameters.track_pilot)
{
// Note that data and pilot components are in quadrature. I and Q are interchanged
current_synchro_data.Prompt_I = static_cast<double>((*d_Prompt_Data).real());
current_synchro_data.Prompt_Q = static_cast<double>((*d_Prompt_Data).imag());
}
else
{
current_synchro_data.Prompt_I = static_cast<double>((*d_Prompt).real());
current_synchro_data.Prompt_Q = static_cast<double>((*d_Prompt).imag());
}
}
current_synchro_data.Code_phase_samples = d_rem_code_phase_samples;
current_synchro_data.Carrier_phase_rads = d_acc_carrier_phase_rad;
current_synchro_data.Carrier_Doppler_hz = d_carrier_doppler_hz;
current_synchro_data.CN0_dB_hz = d_CN0_SNV_dB_Hz;
current_synchro_data.Flag_valid_symbol_output = true;
current_synchro_data.correlation_length_ms = d_correlation_length_ms;
if (next_state)
{ // reset extended correlator
d_VE_accu = gr_complex(0.0, 0.0);
@ -1324,7 +1398,6 @@ int dll_pll_veml_tracking::general_work(int noutput_items __attribute__((unused)
d_last_prompt = gr_complex(0.0, 0.0);
d_Prompt_buffer_deque.clear();
d_current_symbol = 0;
d_synchonizing = false;
if (d_enable_extended_integration)
{

7
src/algorithms/tracking/gnuradio_blocks/dll_pll_veml_tracking.h
View File

@ -41,6 +41,7 @@
#include <string>
#include <map>
#include <queue>
#include <boost/circular_buffer.hpp>
class dll_pll_veml_tracking;
@ -69,6 +70,7 @@ private:
friend dll_pll_veml_tracking_sptr dll_pll_veml_make_tracking(const Dll_Pll_Conf &conf_);
dll_pll_veml_tracking(const Dll_Pll_Conf &conf_);
void msg_handler_preamble_index(pmt::pmt_t msg);
bool cn0_and_tracking_lock_status(double coh_integration_time_s);
bool acquire_secondary();
@ -102,9 +104,12 @@ private:
std::string *d_secondary_code_string;
std::string signal_pretty_name;
uint64_t d_preamble_sample_counter;
int *d_gps_l1ca_preambles_symbols;
boost::circular_buffer<float> d_symbol_history;
//tracking state machine
int d_state;
bool d_synchonizing;
//Integration period in samples
int d_correlation_length_ms;
int d_n_correlator_taps;