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gnss-sdr/src/algorithms/acquisition/gnuradio_blocks/pcps_acquisition.cc

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/*!
* \file pcps_acquisition.cc
* \brief This class implements a Parallel Code Phase Search Acquisition
* \authors <ul>
* <li> Javier Arribas, 2011. jarribas(at)cttc.es
* <li> Luis Esteve, 2012. luis(at)epsilon-formacion.com
* <li> Marc Molina, 2013. marc.molina.pena@gmail.com
* <li> Cillian O'Driscoll, 2017. cillian(at)ieee.org
* </ul>
*
* -------------------------------------------------------------------------
*
* Copyright (C) 2010-2018 (see AUTHORS file for a list of contributors)
*
* GNSS-SDR is a software defined Global Navigation
* Satellite Systems receiver
*
* This file is part of GNSS-SDR.
*
* GNSS-SDR is free software: you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation, either version 3 of the License, or
* (at your option) any later version.
*
* GNSS-SDR is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with GNSS-SDR. If not, see <https://www.gnu.org/licenses/>.
*
* -------------------------------------------------------------------------
*/
#include "pcps_acquisition.h"
#include "GPS_L1_CA.h" // for GPS_TWO_PI
#include "GLONASS_L1_L2_CA.h" // for GLONASS_TWO_PI"
#include <glog/logging.h>
#include <gnuradio/io_signature.h>
#include <matio.h>
#include <volk_gnsssdr/volk_gnsssdr.h>
#include <cstring>
using google::LogMessage;
pcps_acquisition_sptr pcps_make_acquisition(pcpsconf_t conf_)
{
return pcps_acquisition_sptr(new pcps_acquisition(conf_));
}
pcps_acquisition::pcps_acquisition(pcpsconf_t conf_) : gr::block("pcps_acquisition",
gr::io_signature::make(1, 1, conf_.it_size * conf_.sampled_ms * conf_.samples_per_ms * (conf_.bit_transition_flag ? 2 : 1)),
gr::io_signature::make(0, 0, conf_.it_size * conf_.sampled_ms * conf_.samples_per_ms * (conf_.bit_transition_flag ? 2 : 1)))
{
this->message_port_register_out(pmt::mp("events"));
acq_parameters = conf_;
d_sample_counter = 0; // SAMPLE COUNTER
d_active = false;
d_state = 0;
d_old_freq = 0;
d_well_count = 0;
d_fft_size = acq_parameters.sampled_ms * acq_parameters.samples_per_ms;
d_mag = 0;
d_input_power = 0.0;
d_num_doppler_bins = 0;
d_threshold = 0.0;
d_doppler_step = 0;
d_doppler_center_step_two = 0.0;
d_test_statistics = 0.0;
d_channel = 0;
if (conf_.it_size == sizeof(gr_complex))
{
d_cshort = false;
}
else
{
d_cshort = true;
}
// COD:
// Experimenting with the overlap/save technique for handling bit trannsitions
// The problem: Circular correlation is asynchronous with the received code.
// In effect the first code phase used in the correlation is the current
// estimate of the code phase at the start of the input buffer. If this is 1/2
// of the code period a bit transition would move all the signal energy into
// adjacent frequency bands at +/- 1/T where T is the integration time.
//
// We can avoid this by doing linear correlation, effectively doubling the
// size of the input buffer and padding the code with zeros.
if (acq_parameters.bit_transition_flag)
{
d_fft_size *= 2;
acq_parameters.max_dwells = 1; //Activation of acq_parameters.bit_transition_flag invalidates the value of acq_parameters.max_dwells
}
d_fft_codes = static_cast<gr_complex*>(volk_gnsssdr_malloc(d_fft_size * sizeof(gr_complex), volk_gnsssdr_get_alignment()));
d_magnitude = static_cast<float*>(volk_gnsssdr_malloc(d_fft_size * sizeof(float), volk_gnsssdr_get_alignment()));
// Direct FFT
d_fft_if = new gr::fft::fft_complex(d_fft_size, true);
// Inverse FFT
d_ifft = new gr::fft::fft_complex(d_fft_size, false);
d_gnss_synchro = 0;
d_grid_doppler_wipeoffs = nullptr;
d_grid_doppler_wipeoffs_step_two = nullptr;
d_worker_active = false;
d_data_buffer = static_cast<gr_complex*>(volk_gnsssdr_malloc(d_fft_size * sizeof(gr_complex), volk_gnsssdr_get_alignment()));
if (d_cshort)
{
d_data_buffer_sc = static_cast<lv_16sc_t*>(volk_gnsssdr_malloc(d_fft_size * sizeof(lv_16sc_t), volk_gnsssdr_get_alignment()));
}
else
{
d_data_buffer_sc = nullptr;
}
grid_ = arma::fmat();
d_step_two = false;
}
pcps_acquisition::~pcps_acquisition()
{
if (d_num_doppler_bins > 0)
{
for (unsigned int i = 0; i < d_num_doppler_bins; i++)
{
volk_gnsssdr_free(d_grid_doppler_wipeoffs[i]);
}
delete[] d_grid_doppler_wipeoffs;
}
if (acq_parameters.make_2_steps)
{
for (unsigned int i = 0; i < acq_parameters.num_doppler_bins_step2; i++)
{
volk_gnsssdr_free(d_grid_doppler_wipeoffs_step_two[i]);
}
delete[] d_grid_doppler_wipeoffs_step_two;
}
volk_gnsssdr_free(d_fft_codes);
volk_gnsssdr_free(d_magnitude);
delete d_ifft;
delete d_fft_if;
volk_gnsssdr_free(d_data_buffer);
if (d_cshort)
{
volk_gnsssdr_free(d_data_buffer_sc);
}
}
void pcps_acquisition::set_local_code(std::complex<float>* code)
{
// reset the intermediate frequency
d_old_freq = 0;
// This will check if it's fdma, if yes will update the intermediate frequency and the doppler grid
if (is_fdma())
{
update_grid_doppler_wipeoffs();
}
// COD
// Here we want to create a buffer that looks like this:
// [ 0 0 0 ... 0 c_0 c_1 ... c_L]
// where c_i is the local code and there are L zeros and L chips
gr::thread::scoped_lock lock(d_setlock); // require mutex with work function called by the scheduler
if (acq_parameters.bit_transition_flag)
{
int offset = d_fft_size / 2;
std::fill_n(d_fft_if->get_inbuf(), offset, gr_complex(0.0, 0.0));
memcpy(d_fft_if->get_inbuf() + offset, code, sizeof(gr_complex) * offset);
}
else
{
memcpy(d_fft_if->get_inbuf(), code, sizeof(gr_complex) * d_fft_size);
}
d_fft_if->execute(); // We need the FFT of local code
volk_32fc_conjugate_32fc(d_fft_codes, d_fft_if->get_outbuf(), d_fft_size);
}
bool pcps_acquisition::is_fdma()
{
// Dealing with FDMA system
if (strcmp(d_gnss_synchro->Signal, "1G") == 0)
{
d_old_freq += DFRQ1_GLO * GLONASS_PRN.at(d_gnss_synchro->PRN);
LOG(INFO) << "Trying to acquire SV PRN " << d_gnss_synchro->PRN << " with freq " << d_old_freq << " in Glonass Channel " << GLONASS_PRN.at(d_gnss_synchro->PRN) << std::endl;
return true;
}
else if (strcmp(d_gnss_synchro->Signal, "2G") == 0)
{
d_old_freq += DFRQ2_GLO * GLONASS_PRN.at(d_gnss_synchro->PRN);
LOG(INFO) << "Trying to acquire SV PRN " << d_gnss_synchro->PRN << " with freq " << d_old_freq << " in Glonass Channel " << GLONASS_PRN.at(d_gnss_synchro->PRN) << std::endl;
return true;
}
else
{
return false;
}
}
void pcps_acquisition::update_local_carrier(gr_complex* carrier_vector, int correlator_length_samples, float freq)
{
float phase_step_rad = GPS_TWO_PI * freq / static_cast<float>(acq_parameters.fs_in);
float _phase[1];
_phase[0] = 0;
volk_gnsssdr_s32f_sincos_32fc(carrier_vector, -phase_step_rad, _phase, correlator_length_samples);
}
void pcps_acquisition::init()
{
d_gnss_synchro->Flag_valid_acquisition = false;
d_gnss_synchro->Flag_valid_symbol_output = false;
d_gnss_synchro->Flag_valid_pseudorange = false;
d_gnss_synchro->Flag_valid_word = false;
d_gnss_synchro->Acq_delay_samples = 0.0;
d_gnss_synchro->Acq_doppler_hz = 0.0;
d_gnss_synchro->Acq_samplestamp_samples = 0;
d_mag = 0.0;
d_input_power = 0.0;
d_num_doppler_bins = static_cast<unsigned int>(std::ceil(static_cast<double>(static_cast<int>(acq_parameters.doppler_max) - static_cast<int>(-acq_parameters.doppler_max)) / static_cast<double>(d_doppler_step)));
// Create the carrier Doppler wipeoff signals
d_grid_doppler_wipeoffs = new gr_complex*[d_num_doppler_bins];
if (acq_parameters.make_2_steps)
{
d_grid_doppler_wipeoffs_step_two = new gr_complex*[acq_parameters.num_doppler_bins_step2];
for (unsigned int doppler_index = 0; doppler_index < acq_parameters.num_doppler_bins_step2; doppler_index++)
{
d_grid_doppler_wipeoffs_step_two[doppler_index] = static_cast<gr_complex*>(volk_gnsssdr_malloc(d_fft_size * sizeof(gr_complex), volk_gnsssdr_get_alignment()));
}
}
for (unsigned int doppler_index = 0; doppler_index < d_num_doppler_bins; doppler_index++)
{
d_grid_doppler_wipeoffs[doppler_index] = static_cast<gr_complex*>(volk_gnsssdr_malloc(d_fft_size * sizeof(gr_complex), volk_gnsssdr_get_alignment()));
int doppler = -static_cast<int>(acq_parameters.doppler_max) + d_doppler_step * doppler_index;
update_local_carrier(d_grid_doppler_wipeoffs[doppler_index], d_fft_size, d_old_freq + doppler);
}
d_worker_active = false;
if (acq_parameters.dump)
{
unsigned int effective_fft_size = (acq_parameters.bit_transition_flag ? (d_fft_size / 2) : d_fft_size);
grid_ = arma::fmat(effective_fft_size, d_num_doppler_bins, arma::fill::zeros);
}
}
void pcps_acquisition::update_grid_doppler_wipeoffs()
{
for (unsigned int doppler_index = 0; doppler_index < d_num_doppler_bins; doppler_index++)
{
int doppler = -static_cast<int>(acq_parameters.doppler_max) + d_doppler_step * doppler_index;
update_local_carrier(d_grid_doppler_wipeoffs[doppler_index], d_fft_size, d_old_freq + doppler);
}
}
void pcps_acquisition::update_grid_doppler_wipeoffs_step2()
{
for (unsigned int doppler_index = 0; doppler_index < acq_parameters.num_doppler_bins_step2; doppler_index++)
{
float doppler = (static_cast<float>(doppler_index) - static_cast<float>(acq_parameters.num_doppler_bins_step2) / 2.0) * acq_parameters.doppler_step2;
update_local_carrier(d_grid_doppler_wipeoffs_step_two[doppler_index], d_fft_size, d_doppler_center_step_two + doppler);
}
}
void pcps_acquisition::set_state(int state)
{
gr::thread::scoped_lock lock(d_setlock); // require mutex with work function called by the scheduler
d_state = state;
if (d_state == 1)
{
d_gnss_synchro->Acq_delay_samples = 0.0;
d_gnss_synchro->Acq_doppler_hz = 0.0;
d_gnss_synchro->Acq_samplestamp_samples = 0;
d_well_count = 0;
d_mag = 0.0;
d_input_power = 0.0;
d_test_statistics = 0.0;
d_active = true;
}
else if (d_state == 0)
{
}
else
{
LOG(ERROR) << "State can only be set to 0 or 1";
}
}
void pcps_acquisition::send_positive_acquisition()
{
// 6.1- Declare positive acquisition using a message port
//0=STOP_CHANNEL 1=ACQ_SUCCEES 2=ACQ_FAIL
DLOG(INFO) << "positive acquisition"
<< ", satellite " << d_gnss_synchro->System << " " << d_gnss_synchro->PRN
<< ", sample_stamp " << d_sample_counter
<< ", test statistics value " << d_test_statistics
<< ", test statistics threshold " << d_threshold
<< ", code phase " << d_gnss_synchro->Acq_delay_samples
<< ", doppler " << d_gnss_synchro->Acq_doppler_hz
<< ", magnitude " << d_mag
<< ", input signal power " << d_input_power;
this->message_port_pub(pmt::mp("events"), pmt::from_long(1));
}
void pcps_acquisition::send_negative_acquisition()
{
// 6.2- Declare negative acquisition using a message port
//0=STOP_CHANNEL 1=ACQ_SUCCEES 2=ACQ_FAIL
DLOG(INFO) << "negative acquisition"
<< ", satellite " << d_gnss_synchro->System << " " << d_gnss_synchro->PRN
<< ", sample_stamp " << d_sample_counter
<< ", test statistics value " << d_test_statistics
<< ", test statistics threshold " << d_threshold
<< ", code phase " << d_gnss_synchro->Acq_delay_samples
<< ", doppler " << d_gnss_synchro->Acq_doppler_hz
<< ", magnitude " << d_mag
<< ", input signal power " << d_input_power;
this->message_port_pub(pmt::mp("events"), pmt::from_long(2));
}
void pcps_acquisition::acquisition_core(unsigned long int samp_count)
{
gr::thread::scoped_lock lk(d_setlock);
// initialize acquisition algorithm
uint32_t indext = 0;
float magt = 0.0;
const gr_complex* in = d_data_buffer; //Get the input samples pointer
int effective_fft_size = (acq_parameters.bit_transition_flag ? d_fft_size / 2 : d_fft_size);
if (d_cshort)
{
volk_gnsssdr_16ic_convert_32fc(d_data_buffer, d_data_buffer_sc, d_fft_size);
}
float fft_normalization_factor = static_cast<float>(d_fft_size) * static_cast<float>(d_fft_size);
d_input_power = 0.0;
d_mag = 0.0;
d_well_count++;
DLOG(INFO) << "Channel: " << d_channel
<< " , doing acquisition of satellite: " << d_gnss_synchro->System << " " << d_gnss_synchro->PRN
<< " ,sample stamp: " << samp_count << ", threshold: "
<< d_threshold << ", doppler_max: " << acq_parameters.doppler_max
<< ", doppler_step: " << d_doppler_step
<< ", use_CFAR_algorithm_flag: " << (acq_parameters.use_CFAR_algorithm_flag ? "true" : "false");
lk.unlock();
if (acq_parameters.use_CFAR_algorithm_flag)
{
// 1- (optional) Compute the input signal power estimation
volk_32fc_magnitude_squared_32f(d_magnitude, in, d_fft_size);
volk_32f_accumulator_s32f(&d_input_power, d_magnitude, d_fft_size);
d_input_power /= static_cast<float>(d_fft_size);
}
// 2- Doppler frequency search loop
if (!d_step_two)
{
for (unsigned int doppler_index = 0; doppler_index < d_num_doppler_bins; doppler_index++)
{
// doppler search steps
int doppler = -static_cast<int>(acq_parameters.doppler_max) + d_doppler_step * doppler_index;
volk_32fc_x2_multiply_32fc(d_fft_if->get_inbuf(), in, d_grid_doppler_wipeoffs[doppler_index], d_fft_size);
// 3- Perform the FFT-based convolution (parallel time search)
// Compute the FFT of the carrier wiped--off incoming signal
d_fft_if->execute();
// Multiply carrier wiped--off, Fourier transformed incoming signal
// with the local FFT'd code reference using SIMD operations with VOLK library
volk_32fc_x2_multiply_32fc(d_ifft->get_inbuf(), d_fft_if->get_outbuf(), d_fft_codes, d_fft_size);
// compute the inverse FFT
d_ifft->execute();
// Search maximum
size_t offset = (acq_parameters.bit_transition_flag ? effective_fft_size : 0);
volk_32fc_magnitude_squared_32f(d_magnitude, d_ifft->get_outbuf() + offset, effective_fft_size);
volk_gnsssdr_32f_index_max_32u(&indext, d_magnitude, effective_fft_size);
magt = d_magnitude[indext];
if (acq_parameters.use_CFAR_algorithm_flag)
{
// Normalize the maximum value to correct the scale factor introduced by FFTW
magt = d_magnitude[indext] / (fft_normalization_factor * fft_normalization_factor);
}
// 4- record the maximum peak and the associated synchronization parameters
if (d_mag < magt)
{
d_mag = magt;
if (!acq_parameters.use_CFAR_algorithm_flag)
{
// Search grid noise floor approximation for this doppler line
volk_32f_accumulator_s32f(&d_input_power, d_magnitude, effective_fft_size);
d_input_power = (d_input_power - d_mag) / (effective_fft_size - 1);
}
// In case that acq_parameters.bit_transition_flag = true, we compare the potentially
// new maximum test statistics (d_mag/d_input_power) with the value in
// d_test_statistics. When the second dwell is being processed, the value
// of d_mag/d_input_power could be lower than d_test_statistics (i.e,
// the maximum test statistics in the previous dwell is greater than
// current d_mag/d_input_power). Note that d_test_statistics is not
// restarted between consecutive dwells in multidwell operation.
if (d_test_statistics < (d_mag / d_input_power) or !acq_parameters.bit_transition_flag)
{
d_gnss_synchro->Acq_delay_samples = static_cast<double>(indext % acq_parameters.samples_per_code);
d_gnss_synchro->Acq_doppler_hz = static_cast<double>(doppler);
d_gnss_synchro->Acq_samplestamp_samples = samp_count;
// 5- Compute the test statistics and compare to the threshold
//d_test_statistics = 2 * d_fft_size * d_mag / d_input_power;
d_test_statistics = d_mag / d_input_power;
}
}
// Record results to file if required
if (acq_parameters.dump)
{
memcpy(grid_.colptr(doppler_index), d_magnitude, sizeof(float) * effective_fft_size);
if (doppler_index == (d_num_doppler_bins - 1))
{
std::string filename = acq_parameters.dump_filename;
filename.append("_");
filename.append(1, d_gnss_synchro->System);
filename.append("_");
filename.append(1, d_gnss_synchro->Signal[0]);
filename.append(1, d_gnss_synchro->Signal[1]);
filename.append("_sat_");
filename.append(std::to_string(d_gnss_synchro->PRN));
filename.append(".mat");
mat_t* matfp = Mat_CreateVer(filename.c_str(), NULL, MAT_FT_MAT73);
if (matfp == NULL)
{
std::cout << "Unable to create or open Acquisition dump file" << std::endl;
acq_parameters.dump = false;
}
else
{
size_t dims[2] = {static_cast<size_t>(effective_fft_size), static_cast<size_t>(d_num_doppler_bins)};
matvar_t* matvar = Mat_VarCreate("grid", MAT_C_SINGLE, MAT_T_SINGLE, 2, dims, grid_.memptr(), 0);
Mat_VarWrite(matfp, matvar, MAT_COMPRESSION_ZLIB); // or MAT_COMPRESSION_NONE
Mat_VarFree(matvar);
dims[0] = static_cast<size_t>(1);
dims[1] = static_cast<size_t>(1);
matvar = Mat_VarCreate("doppler_max", MAT_C_SINGLE, MAT_T_UINT32, 1, dims, &acq_parameters.doppler_max, 0);
Mat_VarWrite(matfp, matvar, MAT_COMPRESSION_ZLIB); // or MAT_COMPRESSION_NONE
Mat_VarFree(matvar);
matvar = Mat_VarCreate("doppler_step", MAT_C_SINGLE, MAT_T_UINT32, 1, dims, &d_doppler_step, 0);
Mat_VarWrite(matfp, matvar, MAT_COMPRESSION_ZLIB); // or MAT_COMPRESSION_NONE
Mat_VarFree(matvar);
Mat_Close(matfp);
}
}
}
}
}
else
{
for (unsigned int doppler_index = 0; doppler_index < acq_parameters.num_doppler_bins_step2; doppler_index++)
{
// doppler search steps
float doppler = d_doppler_center_step_two + (static_cast<float>(doppler_index) - static_cast<float>(acq_parameters.num_doppler_bins_step2) / 2.0) * acq_parameters.doppler_step2;
volk_32fc_x2_multiply_32fc(d_fft_if->get_inbuf(), in, d_grid_doppler_wipeoffs_step_two[doppler_index], d_fft_size);
// 3- Perform the FFT-based convolution (parallel time search)
// Compute the FFT of the carrier wiped--off incoming signal
d_fft_if->execute();
// Multiply carrier wiped--off, Fourier transformed incoming signal
// with the local FFT'd code reference using SIMD operations with VOLK library
volk_32fc_x2_multiply_32fc(d_ifft->get_inbuf(), d_fft_if->get_outbuf(), d_fft_codes, d_fft_size);
// compute the inverse FFT
d_ifft->execute();
// Search maximum
size_t offset = (acq_parameters.bit_transition_flag ? effective_fft_size : 0);
volk_32fc_magnitude_squared_32f(d_magnitude, d_ifft->get_outbuf() + offset, effective_fft_size);
volk_gnsssdr_32f_index_max_32u(&indext, d_magnitude, effective_fft_size);
magt = d_magnitude[indext];
if (acq_parameters.use_CFAR_algorithm_flag)
{
// Normalize the maximum value to correct the scale factor introduced by FFTW
magt = d_magnitude[indext] / (fft_normalization_factor * fft_normalization_factor);
}
// 4- record the maximum peak and the associated synchronization parameters
if (d_mag < magt)
{
d_mag = magt;
if (!acq_parameters.use_CFAR_algorithm_flag)
{
// Search grid noise floor approximation for this doppler line
volk_32f_accumulator_s32f(&d_input_power, d_magnitude, effective_fft_size);
d_input_power = (d_input_power - d_mag) / (effective_fft_size - 1);
}
// In case that acq_parameters.bit_transition_flag = true, we compare the potentially
// new maximum test statistics (d_mag/d_input_power) with the value in
// d_test_statistics. When the second dwell is being processed, the value
// of d_mag/d_input_power could be lower than d_test_statistics (i.e,
// the maximum test statistics in the previous dwell is greater than
// current d_mag/d_input_power). Note that d_test_statistics is not
// restarted between consecutive dwells in multidwell operation.
if (d_test_statistics < (d_mag / d_input_power) or !acq_parameters.bit_transition_flag)
{
d_gnss_synchro->Acq_delay_samples = static_cast<double>(indext % acq_parameters.samples_per_code);
d_gnss_synchro->Acq_doppler_hz = static_cast<double>(doppler);
d_gnss_synchro->Acq_samplestamp_samples = samp_count;
// 5- Compute the test statistics and compare to the threshold
//d_test_statistics = 2 * d_fft_size * d_mag / d_input_power;
d_test_statistics = d_mag / d_input_power;
}
}
}
}
lk.lock();
if (!acq_parameters.bit_transition_flag)
{
if (d_test_statistics > d_threshold)
{
d_active = false;
if (acq_parameters.make_2_steps)
{
if (d_step_two)
{
send_positive_acquisition();
d_step_two = false;
d_state = 0; // Positive acquisition
}
else
{
d_step_two = true; // Clear input buffer and make small grid acquisition
d_state = 0;
}
}
else
{
send_positive_acquisition();
d_state = 0; // Positive acquisition
}
}
else if (d_well_count == acq_parameters.max_dwells)
{
d_state = 0;
d_active = false;
d_step_two = false;
send_negative_acquisition();
}
}
else
{
d_active = false;
if (d_test_statistics > d_threshold)
{
if (acq_parameters.make_2_steps)
{
if (d_step_two)
{
send_positive_acquisition();
d_step_two = false;
d_state = 0; // Positive acquisition
}
else
{
d_step_two = true; // Clear input buffer and make small grid acquisition
d_state = 0;
}
}
else
{
send_positive_acquisition();
d_state = 0; // Positive acquisition
}
}
else
{
d_state = 0; // Negative acquisition
d_step_two = false;
send_negative_acquisition();
}
}
d_worker_active = false;
}
int pcps_acquisition::general_work(int noutput_items __attribute__((unused)),
gr_vector_int& ninput_items, gr_vector_const_void_star& input_items,
gr_vector_void_star& output_items __attribute__((unused)))
{
/*
* By J.Arribas, L.Esteve and M.Molina
* Acquisition strategy (Kay Borre book + CFAR threshold):
* 1. Compute the input signal power estimation
* 2. Doppler serial search loop
* 3. Perform the FFT-based circular convolution (parallel time search)
* 4. Record the maximum peak and the associated synchronization parameters
* 5. Compute the test statistics and compare to the threshold
* 6. Declare positive or negative acquisition using a message port
*/
gr::thread::scoped_lock lk(d_setlock);
if (!d_active or d_worker_active)
{
d_sample_counter += d_fft_size * ninput_items[0];
consume_each(ninput_items[0]);
if (d_step_two)
{
d_doppler_center_step_two = static_cast<float>(d_gnss_synchro->Acq_doppler_hz);
update_grid_doppler_wipeoffs_step2();
d_state = 0;
d_active = true;
}
return 0;
}
switch (d_state)
{
case 0:
{
//restart acquisition variables
d_gnss_synchro->Acq_delay_samples = 0.0;
d_gnss_synchro->Acq_doppler_hz = 0.0;
d_gnss_synchro->Acq_samplestamp_samples = 0;
d_well_count = 0;
d_mag = 0.0;
d_input_power = 0.0;
d_test_statistics = 0.0;
d_state = 1;
d_sample_counter += d_fft_size * ninput_items[0]; // sample counter
consume_each(ninput_items[0]);
break;
}
case 1:
{
// Copy the data to the core and let it know that new data is available
if (d_cshort)
{
memcpy(d_data_buffer_sc, input_items[0], d_fft_size * sizeof(lv_16sc_t));
}
else
{
memcpy(d_data_buffer, input_items[0], d_fft_size * sizeof(gr_complex));
}
if (acq_parameters.blocking)
{
lk.unlock();
acquisition_core(d_sample_counter);
}
else
{
gr::thread::thread d_worker(&pcps_acquisition::acquisition_core, this, d_sample_counter);
d_worker_active = true;
}
d_sample_counter += d_fft_size;
consume_each(1);
break;
}
}
return 0;
}
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