Permalink
Fetching contributors…
Cannot retrieve contributors at this time
503 lines (425 sloc) 20.1 KB
/*!
* \file pcps_acquisition_cc.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
* </ul>
*
* -------------------------------------------------------------------------
*
* Copyright (C) 2010-2015 (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 <http://www.gnu.org/licenses/>.
*
* -------------------------------------------------------------------------
*/
#include "pcps_acquisition_cc.h"
#include <sstream>
#include <boost/filesystem.hpp>
#include <gnuradio/io_signature.h>
#include <glog/logging.h>
#include <volk/volk.h>
#include <volk_gnsssdr/volk_gnsssdr.h>
#include "control_message_factory.h"
#include "GPS_L1_CA.h" //GPS_TWO_PI
using google::LogMessage;
pcps_acquisition_cc_sptr pcps_make_acquisition_cc(
unsigned int sampled_ms, unsigned int max_dwells,
unsigned int doppler_max, long freq, long fs_in,
int samples_per_ms, int samples_per_code,
bool bit_transition_flag, bool use_CFAR_algorithm_flag,
bool dump,
std::string dump_filename)
{
return pcps_acquisition_cc_sptr(
new pcps_acquisition_cc(sampled_ms, max_dwells, doppler_max, freq, fs_in, samples_per_ms,
samples_per_code, bit_transition_flag, use_CFAR_algorithm_flag, dump, dump_filename));
}
pcps_acquisition_cc::pcps_acquisition_cc(
unsigned int sampled_ms, unsigned int max_dwells,
unsigned int doppler_max, long freq, long fs_in,
int samples_per_ms, int samples_per_code,
bool bit_transition_flag, bool use_CFAR_algorithm_flag,
bool dump,
std::string dump_filename) :
gr::block("pcps_acquisition_cc",
gr::io_signature::make(1, 1, sizeof(gr_complex) * sampled_ms * samples_per_ms * ( bit_transition_flag ? 2 : 1 )),
gr::io_signature::make(0, 0, sizeof(gr_complex) * sampled_ms * samples_per_ms * ( bit_transition_flag ? 2 : 1 )) )
{
this->message_port_register_out(pmt::mp("events"));
d_sample_counter = 0; // SAMPLE COUNTER
d_active = false;
d_state = 0;
d_freq = freq;
d_fs_in = fs_in;
d_samples_per_ms = samples_per_ms;
d_samples_per_code = samples_per_code;
d_sampled_ms = sampled_ms;
d_max_dwells = max_dwells;
d_well_count = 0;
d_doppler_max = doppler_max;
d_fft_size = d_sampled_ms * d_samples_per_ms;
d_mag = 0;
d_input_power = 0.0;
d_num_doppler_bins = 0;
d_bit_transition_flag = bit_transition_flag;
d_use_CFAR_algorithm_flag = use_CFAR_algorithm_flag;
d_threshold = 0.0;
d_doppler_step = 0;
d_code_phase = 0;
d_test_statistics = 0.0;
d_channel = 0;
d_doppler_freq = 0.0;
//set_relative_rate( 1.0/d_fft_size );
// 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( d_bit_transition_flag )
{
d_fft_size *= 2;
d_max_dwells = 1; //Activation of d_bit_transition_flag invalidates the value of d_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);
// For dumping samples into a file
d_dump = dump;
d_dump_filename = dump_filename;
d_gnss_synchro = 0;
d_grid_doppler_wipeoffs = 0;
}
pcps_acquisition_cc::~pcps_acquisition_cc()
{
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;
}
volk_gnsssdr_free(d_fft_codes);
volk_gnsssdr_free(d_magnitude);
delete d_ifft;
delete d_fft_if;
if (d_dump)
{
d_dump_file.close();
}
}
void pcps_acquisition_cc::set_local_code(std::complex<float> * code)
{
// 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
if( d_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);
}
void pcps_acquisition_cc::update_local_carrier(gr_complex* carrier_vector, int correlator_length_samples, float freq)
{
float phase_step_rad = GPS_TWO_PI * freq / static_cast<float>(d_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_cc::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->Flag_preamble = 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 = ceil( static_cast<double>(static_cast<int>(d_doppler_max) - static_cast<int>(-d_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];
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>(d_doppler_max) + d_doppler_step * doppler_index;
update_local_carrier(d_grid_doppler_wipeoffs[doppler_index], d_fft_size, d_freq + doppler);
}
}
void pcps_acquisition_cc::set_state(int state)
{
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;
}
else if (d_state == 0)
{}
else
{
LOG(ERROR) << "State can only be set to 0 or 1";
}
}
int pcps_acquisition_cc::general_work(int noutput_items,
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
*/
int acquisition_message = -1; //0=STOP_CHANNEL 1=ACQ_SUCCEES 2=ACQ_FAIL
switch (d_state)
{
case 0:
{
if (d_active)
{
//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]);
//DLOG(INFO) << "Consumed " << ninput_items[0] << " items";
break;
}
case 1:
{
// initialize acquisition algorithm
int doppler;
uint32_t indext = 0;
float magt = 0.0;
const gr_complex *in = (const gr_complex *)input_items[0]; //Get the input samples pointer
int effective_fft_size = ( d_bit_transition_flag ? d_fft_size/2 : 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_sample_counter += d_fft_size; // sample counter
d_well_count++;
DLOG(INFO) << "Channel: " << d_channel
<< " , doing acquisition of satellite: " << d_gnss_synchro->System << " " << d_gnss_synchro->PRN
<< " ,sample stamp: " << d_sample_counter << ", threshold: "
<< d_threshold << ", doppler_max: " << d_doppler_max
<< ", doppler_step: " << d_doppler_step;
if (d_use_CFAR_algorithm_flag == true)
{
// 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
for (unsigned int doppler_index = 0; doppler_index < d_num_doppler_bins; doppler_index++)
{
// doppler search steps
doppler = -static_cast<int>(d_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 = ( d_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 (d_use_CFAR_algorithm_flag == true)
{
// 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 (d_use_CFAR_algorithm_flag == false)
{
// 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 d_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) || !d_bit_transition_flag)
{
d_gnss_synchro->Acq_delay_samples = static_cast<double>(indext % d_samples_per_code);
d_gnss_synchro->Acq_doppler_hz = static_cast<double>(doppler);
d_gnss_synchro->Acq_samplestamp_samples = d_sample_counter;
// 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 (d_dump)
{
std::stringstream filename;
std::streamsize n = 2 * sizeof(float) * (d_fft_size); // complex file write
filename.str("");
boost::filesystem::path p = d_dump_filename;
filename << p.parent_path().string()
<< boost::filesystem::path::preferred_separator
<< p.stem().string()
<< "_" << d_gnss_synchro->System
<<"_" << d_gnss_synchro->Signal << "_sat_"
<< d_gnss_synchro->PRN << "_doppler_"
<< doppler
<< p.extension().string();
DLOG(INFO) << "Writing ACQ out to " << filename.str();
d_dump_file.open(filename.str().c_str(), std::ios::out | std::ios::binary);
d_dump_file.write((char*)d_ifft->get_outbuf(), n); //write directly |abs(x)|^2 in this Doppler bin?
d_dump_file.close();
}
}
if (!d_bit_transition_flag)
{
if (d_test_statistics > d_threshold)
{
d_state = 2; // Positive acquisition
}
else if (d_well_count == d_max_dwells)
{
d_state = 3; // Negative acquisition
}
}
else
{
if (d_well_count == d_max_dwells) // d_max_dwells = 2
{
if (d_test_statistics > d_threshold)
{
d_state = 2; // Positive acquisition
}
else
{
d_state = 3; // Negative acquisition
}
}
}
consume_each(1);
DLOG(INFO) << "Done. Consumed 1 item.";
break;
}
case 2:
{
// 6.1- Declare positive acquisition using a message port
DLOG(INFO) << "positive acquisition";
DLOG(INFO) << "satellite " << d_gnss_synchro->System << " " << d_gnss_synchro->PRN;
DLOG(INFO) << "sample_stamp " << d_sample_counter;
DLOG(INFO) << "test statistics value " << d_test_statistics;
DLOG(INFO) << "test statistics threshold " << d_threshold;
DLOG(INFO) << "code phase " << d_gnss_synchro->Acq_delay_samples;
DLOG(INFO) << "doppler " << d_gnss_synchro->Acq_doppler_hz;
DLOG(INFO) << "magnitude " << d_mag;
DLOG(INFO) << "input signal power " << d_input_power;
d_active = false;
d_state = 0;
d_sample_counter += d_fft_size * ninput_items[0]; // sample counter
consume_each(ninput_items[0]);
acquisition_message = 1;
this->message_port_pub(pmt::mp("events"), pmt::from_long(acquisition_message));
break;
}
case 3:
{
// 6.2- Declare negative acquisition using a message port
DLOG(INFO) << "negative acquisition";
DLOG(INFO) << "satellite " << d_gnss_synchro->System << " " << d_gnss_synchro->PRN;
DLOG(INFO) << "sample_stamp " << d_sample_counter;
DLOG(INFO) << "test statistics value " << d_test_statistics;
DLOG(INFO) << "test statistics threshold " << d_threshold;
DLOG(INFO) << "code phase " << d_gnss_synchro->Acq_delay_samples;
DLOG(INFO) << "doppler " << d_gnss_synchro->Acq_doppler_hz;
DLOG(INFO) << "magnitude " << d_mag;
DLOG(INFO) << "input signal power " << d_input_power;
d_active = false;
d_state = 0;
d_sample_counter += d_fft_size * ninput_items[0]; // sample counter
consume_each(ninput_items[0]);
acquisition_message = 2;
this->message_port_pub(pmt::mp("events"), pmt::from_long(acquisition_message));
break;
}
}
return noutput_items;
}
//void pcps_acquisition_cc::forecast (int noutput_items, gr_vector_int &ninput_items_required)
//{
//// COD:
//// For zero-padded case we need one extra code period
//if( d_bit_transition_flag )
//{
//ninput_items_required[0] = noutput_items*(d_samples_per_code * d_max_dwells + d_samples_per_code);
//}
//else
//{
//ninput_items_required[0] = noutput_items*d_fft_size*d_max_dwells;
//}
//}