mirror of https://github.com/gnss-sdr/gnss-sdr
294 lines
10 KiB
C++
294 lines
10 KiB
C++
/*!
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* \file gps_l1_ca_telemetry_decoder_cc.cc
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* \brief Implementation of a NAV message demodulator block based on
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* Kay Borre book MATLAB-based GPS receiver
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* \author Javier Arribas, 2011. jarribas(at)cttc.es
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*
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* -------------------------------------------------------------------------
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*
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* Copyright (C) 2010-2011 (see AUTHORS file for a list of contributors)
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*
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* GNSS-SDR is a software defined Global Navigation
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* Satellite Systems receiver
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*
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* This file is part of GNSS-SDR.
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*
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* GNSS-SDR is free software: you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation, either version 3 of the License, or
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* at your option) any later version.
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*
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* GNSS-SDR is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with GNSS-SDR. If not, see <http://www.gnu.org/licenses/>.
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*
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* -------------------------------------------------------------------------
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*/
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/*!
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* \todo Clean this code and move the telemetry definitions to GPS_L1_CA system definitions file
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*/
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#include <iostream>
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#include <sstream>
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#include <bitset>
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#include <gnuradio/gr_io_signature.h>
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#include <glog/log_severity.h>
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#include <glog/logging.h>
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#include "gps_l1_ca_telemetry_decoder_cc.h"
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#include "control_message_factory.h"
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using google::LogMessage;
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/*!
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* \todo name and move the magic numbers to GPS_L1_CA.h
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*/
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gps_l1_ca_telemetry_decoder_cc_sptr
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gps_l1_ca_make_telemetry_decoder_cc(unsigned int satellite, long if_freq, long fs_in, unsigned
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int vector_length, gr_msg_queue_sptr queue, bool dump) {
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return gps_l1_ca_telemetry_decoder_cc_sptr(new gps_l1_ca_telemetry_decoder_cc(satellite, if_freq,
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fs_in, vector_length, queue, dump));
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}
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void gps_l1_ca_telemetry_decoder_cc::forecast (int noutput_items,
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gr_vector_int &ninput_items_required){
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for (unsigned i = 0; i < 3; i++) {
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ninput_items_required[i] =d_samples_per_bit*8; //set the required sample history
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}
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}
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gps_l1_ca_telemetry_decoder_cc::gps_l1_ca_telemetry_decoder_cc(unsigned int satellite, long if_freq, long fs_in, unsigned
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int vector_length, gr_msg_queue_sptr queue, bool dump) :
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gr_block ("gps_navigation_cc", gr_make_io_signature (5, 5, sizeof(double)),
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gr_make_io_signature(1, 1, sizeof(gnss_synchro))) {
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// initialize internal vars
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d_queue = queue;
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d_dump = dump;
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d_satellite = satellite;
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d_vector_length = vector_length;
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d_samples_per_bit=20; // it is exactly 1000*(1/50)=20
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d_fs_in=fs_in;
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d_preamble_duration_seconds=(1.0/(float)GPS_CA_TELEMETRY_RATE_BITS_SECOND)*(float)GPS_CA_PREAMBLE_LENGTH_BITS;
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//std::cout<<"d_preamble_duration_seconds="<<d_preamble_duration_seconds<<"\r\n";
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// set the preamble
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unsigned short int preambles_bits[8]=GPS_PREAMBLE;
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memcpy((unsigned short int*)this->d_preambles_bits, (unsigned short int*)preambles_bits, 8* sizeof(unsigned short int));
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// preamble bits to sampled symbols
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d_preambles_symbols=(signed int*)malloc(sizeof(signed int)*8*d_samples_per_bit);
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int n=0;
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for (int i=0;i<8;i++)
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{
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for (unsigned int j=0;j<d_samples_per_bit;j++)
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{
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if (d_preambles_bits[i]==1)
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{
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d_preambles_symbols[n]=1;
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}else{
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d_preambles_symbols[n]=-1;
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}
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n++;
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}
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}
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d_sample_counter=0;
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d_preamble_code_phase_seconds=0;
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d_stat=0;
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d_preamble_index=0;
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d_symbol_accumulator_counter=0;
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d_frame_bit_index=0;
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d_flag_frame_sync=false;
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d_GPS_frame_4bytes=0;
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d_prev_GPS_frame_4bytes=0;
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d_flag_parity=false;
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//set_history(d_samples_per_bit*8); // At least a history of 8 bits are needed to correlate with the preamble
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}
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gps_l1_ca_telemetry_decoder_cc::~gps_l1_ca_telemetry_decoder_cc() {
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delete d_preambles_symbols;
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d_dump_file.close();
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}
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int gps_l1_ca_telemetry_decoder_cc::general_work (int noutput_items, gr_vector_int &ninput_items,
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gr_vector_const_void_star &input_items, gr_vector_void_star &output_items) {
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int corr_value=0;
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int preamble_diff;
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gnss_synchro gps_synchro; //structure to save the synchronization information
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gnss_synchro **out = (gnss_synchro **) &output_items[0];
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d_sample_counter++; //count for the processed samples
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const double **in = (const double **) &input_items[0]; //Get the input samples pointer
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// ########### Output the tracking data to navigation and PVT ##########
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// Output channel 0: Prompt correlator output Q
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// *out[0]=(double)d_Prompt.real();
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// // Output channel 1: Prompt correlator output I
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// *out[1]=(double)d_Prompt.imag();
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// // Output channel 2: PRN absolute delay [s]
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// *out[2]=d_sample_counter_seconds;
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// // Output channel 3: d_acc_carrier_phase_rad [rad]
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// *out[3]=(double)d_acc_carrier_phase_rad;
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// // Output channel 4: PRN code phase [s]
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// *out[4]=(double)d_code_phase_samples*(1/(float)d_fs_in);
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/*!
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* \todo Check the HOW GPS time computation, taking into account that the preamble correlation last 160 symbols, which is 160 ms in GPS CA L1
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*/
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// FIFO history to get the exact timestamp of the first symbol of the preamble
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// if (d_prn_start_sample_history.size()<160)
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// {
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// // fill the queue
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// d_prn_start_sample_history.push_front(in[2][0]);
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// consume_each(1); //one by one
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// return 1;
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// }else{
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// d_prn_start_sample_history.pop_back();
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// d_prn_start_sample_history.push_front(in[2][0]);
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// }
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// TODO Optimize me!
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//******* preamble correlation ********
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for (unsigned int i=0;i<d_samples_per_bit*8;i++){
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if (in[1][i] < 0) // symbols clipping
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{
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corr_value-=d_preambles_symbols[i];
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}else{
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corr_value+=d_preambles_symbols[i];
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}
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}
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d_flag_preamble=false;
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//******* frame sync ******************
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if (abs(corr_value)>=160){
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//TODO: Rewrite with state machine
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if (d_stat==0)
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{
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d_GPS_FSM.Event_gps_word_preamble();
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d_preamble_index=d_sample_counter;//record the preamble sample stamp
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std::cout<<"Preamble detection for SAT "<<d_satellite<<std::endl;
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d_symbol_accumulator=0; //sync the symbol to bits integrator
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d_symbol_accumulator_counter=0;
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d_frame_bit_index=8;
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d_stat=1; // enter into frame pre-detection status
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}else if (d_stat==1) //check 6 seconds of preample separation
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{
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preamble_diff=abs(d_sample_counter-d_preamble_index);
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if (abs(preamble_diff-6000)<1)
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{
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d_GPS_FSM.Event_gps_word_preamble();
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d_flag_preamble=true;
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d_preamble_index=d_sample_counter;//record the preamble sample stamp (t_P)
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d_preamble_time_seconds=in[2][0]-d_preamble_duration_seconds; //record the PRN start sample index associated to the preamble
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d_preamble_code_phase_seconds=in[4][0];
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if (!d_flag_frame_sync){
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d_flag_frame_sync=true;
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std::cout<<" Frame sync SAT "<<d_satellite<<" with preamble start at "<<d_preamble_time_seconds<<" [s]"<<std::endl;
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}
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}
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}
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}else{
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if (d_stat==1)
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{
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preamble_diff=d_sample_counter-d_preamble_index;
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if (preamble_diff>6001){
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std::cout<<"Lost of frame sync SAT "<<this->d_satellite<<" preamble_diff= "<<preamble_diff<<std::endl;
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d_stat=0; //lost of frame sync
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d_flag_frame_sync=false;
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}
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}
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}
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//******* code error accumulator *****
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//d_preamble_phase-=in[3][0];
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//******* SYMBOL TO BIT *******
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d_symbol_accumulator+=in[1][d_samples_per_bit*8-1]; // accumulate the input value in d_symbol_accumulator
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d_symbol_accumulator_counter++;
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if (d_symbol_accumulator_counter==20)
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{
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if (d_symbol_accumulator>0){ //symbol to bit
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d_GPS_frame_4bytes+=1; //insert the telemetry bit in LSB
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}
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d_symbol_accumulator=0;
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d_symbol_accumulator_counter=0;
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//******* bits to words ******
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d_frame_bit_index++;
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if (d_frame_bit_index==30)
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{
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d_frame_bit_index=0;
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//parity check
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//Each word in wordbuff is composed of:
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// Bits 0 to 29 = the GPS data word
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// Bits 30 to 31 = 2 LSBs of the GPS word ahead.
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// prepare the extended frame [-2 -1 0 ... 30]
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if (d_prev_GPS_frame_4bytes & 0x00000001)
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{
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d_GPS_frame_4bytes=d_GPS_frame_4bytes|0x40000000;
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}
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if (d_prev_GPS_frame_4bytes & 0x00000002)
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{
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d_GPS_frame_4bytes=d_GPS_frame_4bytes|0x80000000;
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}
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/* Check that the 2 most recently logged words pass parity. Have to first
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invert the data bits according to bit 30 of the previous word. */
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if(d_GPS_frame_4bytes & 0x40000000)
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{
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d_GPS_frame_4bytes ^= 0x3FFFFFC0; // invert the data bits (using XOR)
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}
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if (gps_word_parityCheck(d_GPS_frame_4bytes)) {
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memcpy(&d_GPS_FSM.d_GPS_frame_4bytes,&d_GPS_frame_4bytes,sizeof(char)*4);
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d_GPS_FSM.d_preamble_time_ms=d_preamble_time_seconds*1000.0;
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d_GPS_FSM.Event_gps_word_valid();
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d_flag_parity=true;
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}else{
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d_GPS_FSM.Event_gps_word_invalid();
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d_flag_parity=false;
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}
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d_prev_GPS_frame_4bytes=d_GPS_frame_4bytes; // save the actual frame
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d_GPS_frame_4bytes=d_GPS_frame_4bytes & 0;
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}else{
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d_GPS_frame_4bytes<<=1; //shift 1 bit left the telemetry word
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}
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}
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// output the frame
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consume_each(1); //one by one
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gps_synchro.valid_word=(d_flag_frame_sync==true and d_flag_parity==true);
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gps_synchro.flag_preamble=d_flag_preamble;
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gps_synchro.preamble_delay_ms=d_preamble_time_seconds*1000.0;
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gps_synchro.prn_delay_ms=(in[2][0]-d_preamble_duration_seconds)*1000.0;
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gps_synchro.preamble_code_phase_ms=d_preamble_code_phase_seconds*1000.0;
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gps_synchro.preamble_code_phase_correction_ms=(in[4][0]-d_preamble_code_phase_seconds)*1000.0;
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gps_synchro.satellite_PRN=d_satellite;
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gps_synchro.channel_ID=d_channel;
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*out[0]=gps_synchro;
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return 1;
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}
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void gps_l1_ca_telemetry_decoder_cc::set_satellite(int satellite) {
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d_satellite = satellite;
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d_GPS_FSM.d_satellite_PRN=satellite;
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LOG_AT_LEVEL(INFO) << "Navigation Satellite set to " << d_satellite;
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}
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void gps_l1_ca_telemetry_decoder_cc::set_channel(int channel) {
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d_channel = channel;
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d_GPS_FSM.d_channel_ID=channel;
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LOG_AT_LEVEL(INFO) << "Navigation channel set to " << channel;
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}
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