mirror of https://github.com/gnss-sdr/gnss-sdr
353 lines
14 KiB
C++
353 lines
14 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) 2010-2012 (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 "gps_l1_ca_telemetry_decoder_cc.h"
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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 "control_message_factory.h"
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#define _lrotl(X,N) ((X << N) ^ (X >> (32-N))) // Used in the parity check algorithm
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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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{
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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, gr_vector_int &ninput_items_required)
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{
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for (unsigned i = 0; i < 3; i++)
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{
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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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{
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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 = ( GPS_L1_CA_CODE_RATE_HZ / GPS_L1_CA_CODE_LENGTH_CHIPS ) / GPS_CA_TELEMETRY_RATE_BITS_SECOND;
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d_fs_in = fs_in;
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d_preamble_duration_seconds = (1.0 / GPS_CA_TELEMETRY_RATE_BITS_SECOND) * 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[GPS_CA_PREAMBLE_LENGTH_BITS] = GPS_PREAMBLE;
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memcpy((unsigned short int*)this->d_preambles_bits, (unsigned short int*)preambles_bits, GPS_CA_PREAMBLE_LENGTH_BITS*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) * GPS_CA_PREAMBLE_LENGTH_BITS * d_samples_per_bit);
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int n = 0;
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for (int i=0; i<GPS_CA_PREAMBLE_LENGTH_BITS; 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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}
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else
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{
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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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{
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delete d_preambles_symbols;
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d_dump_file.close();
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}
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bool gps_l1_ca_telemetry_decoder_cc::gps_word_parityCheck(unsigned int gpsword)
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{
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unsigned int d1, d2, d3, d4, d5, d6, d7, t, parity;
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/* XOR as many bits in parallel as possible. The magic constants pick
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up bits which are to be XOR'ed together to implement the GPS parity
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check algorithm described in IS-GPS-200E. This avoids lengthy shift-
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and-xor loops. */
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d1 = gpsword & 0xFBFFBF00;
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d2 = _lrotl(gpsword,1) & 0x07FFBF01;
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d3 = _lrotl(gpsword,2) & 0xFC0F8100;
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d4 = _lrotl(gpsword,3) & 0xF81FFE02;
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d5 = _lrotl(gpsword,4) & 0xFC00000E;
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d6 = _lrotl(gpsword,5) & 0x07F00001;
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d7 = _lrotl(gpsword,6) & 0x00003000;
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t = d1 ^ d2 ^ d3 ^ d4 ^ d5 ^ d6 ^ d7;
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// Now XOR the 5 6-bit fields together to produce the 6-bit final result.
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parity = t ^ _lrotl(t,6) ^ _lrotl(t,12) ^ _lrotl(t,18) ^ _lrotl(t,24);
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parity = parity & 0x3F;
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if (parity == (gpsword&0x3F)) return(true);
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else return(false);
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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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{
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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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{
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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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}
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else
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{
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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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{
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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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}
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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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{
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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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}
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else
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{
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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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{
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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)
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{ //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_l1_ca_telemetry_decoder_cc::gps_word_parityCheck(d_GPS_frame_4bytes))
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{
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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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}
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else
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{
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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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}
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else
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{
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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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//! \todo This has to be documented and included in the header!!!!
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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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{
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d_satellite = satellite;
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d_GPS_FSM.i_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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{
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d_channel = channel;
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d_GPS_FSM.i_channel_ID = channel;
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LOG_AT_LEVEL(INFO) << "Navigation channel set to " << channel;
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}
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