mirror of https://github.com/gnss-sdr/gnss-sdr
256 lines
10 KiB
C++
256 lines
10 KiB
C++
/*!
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* \file beidou_b3i_signal_processing.cc
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* \brief This class implements various functions for BeiDou B1I signal
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* \author Damian Miralles, 2019. dmiralles2009@gmail.com
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*
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* Detailed description of the file here if needed.
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*
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* -------------------------------------------------------------------------
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*
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* Copyright (C) 2010-2015 (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 <https://www.gnu.org/licenses/>.
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*
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* -------------------------------------------------------------------------
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*/
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#include "beidou_b3i_signal_processing.h"
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#include <array>
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#include <bitset>
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#include <string>
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auto auxCeil = [](float x) { return static_cast<int32_t>(static_cast<int64_t>((x) + 1)); };
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void beidou_b3i_code_gen_int(gsl::span<int> _dest, int32_t _prn, uint32_t _chip_shift)
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{
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const uint32_t _code_length = 10230;
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std::bitset<_code_length> G1{};
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std::bitset<_code_length> G2{};
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auto G1_register = std::bitset<13>{}.set(); // All true
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auto G2_register = std::bitset<13>{}.set(); // All true
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auto G1_register_reset = std::bitset<13>{}.set();
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G1_register_reset.reset(0);
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G1_register_reset.reset(1); // {false, false, true, true, true, true, true, true, true, true, true, true, true};
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bool feedback1;
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bool feedback2;
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bool aux;
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uint32_t lcv;
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uint32_t lcv2;
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uint32_t delay;
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int32_t prn_idx = _prn - 1;
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const std::array<std::bitset<13>, 63> G2_register_shifted =
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{std::bitset<13>(std::string("1010111111111")),
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std::bitset<13>(std::string("1111000101011")),
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std::bitset<13>(std::string("1011110001010")),
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std::bitset<13>(std::string("1111111111011")),
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std::bitset<13>(std::string("1100100011111")),
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std::bitset<13>(std::string("1001001100100")),
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std::bitset<13>(std::string("1111111010010")),
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std::bitset<13>(std::string("1110111111101")),
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std::bitset<13>(std::string("1010000000010")),
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std::bitset<13>(std::string("0010000011011")),
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std::bitset<13>(std::string("1110101110000")),
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std::bitset<13>(std::string("0010110011110")),
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std::bitset<13>(std::string("0110010010101")),
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std::bitset<13>(std::string("0111000100110")),
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std::bitset<13>(std::string("1000110001001")),
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std::bitset<13>(std::string("1110001111100")),
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std::bitset<13>(std::string("0010011000101")),
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std::bitset<13>(std::string("0000011101100")),
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std::bitset<13>(std::string("1000101010111")),
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std::bitset<13>(std::string("0001011011110")),
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std::bitset<13>(std::string("0010000101101")),
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std::bitset<13>(std::string("0010110001010")),
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std::bitset<13>(std::string("0001011001111")),
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std::bitset<13>(std::string("0011001100010")),
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std::bitset<13>(std::string("0011101001000")),
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std::bitset<13>(std::string("0100100101001")),
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std::bitset<13>(std::string("1011011010011")),
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std::bitset<13>(std::string("1010111100010")),
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std::bitset<13>(std::string("0001011110101")),
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std::bitset<13>(std::string("0111111111111")),
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std::bitset<13>(std::string("0110110001111")),
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std::bitset<13>(std::string("1010110001001")),
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std::bitset<13>(std::string("1001010101011")),
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std::bitset<13>(std::string("1100110100101")),
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std::bitset<13>(std::string("1101001011101")),
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std::bitset<13>(std::string("1111101110100")),
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std::bitset<13>(std::string("0010101100111")),
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std::bitset<13>(std::string("1110100010000")),
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std::bitset<13>(std::string("1101110010000")),
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std::bitset<13>(std::string("1101011001110")),
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std::bitset<13>(std::string("1000000110100")),
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std::bitset<13>(std::string("0101111011001")),
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std::bitset<13>(std::string("0110110111100")),
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std::bitset<13>(std::string("1101001110001")),
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std::bitset<13>(std::string("0011100100010")),
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std::bitset<13>(std::string("0101011000101")),
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std::bitset<13>(std::string("1001111100110")),
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std::bitset<13>(std::string("1111101001000")),
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std::bitset<13>(std::string("0000101001001")),
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std::bitset<13>(std::string("1000010101100")),
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std::bitset<13>(std::string("1111001001100")),
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std::bitset<13>(std::string("0100110001111")),
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std::bitset<13>(std::string("0000000011000")),
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std::bitset<13>(std::string("1000000000100")),
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std::bitset<13>(std::string("0011010100110")),
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std::bitset<13>(std::string("1011001000110")),
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std::bitset<13>(std::string("0111001111000")),
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std::bitset<13>(std::string("0010111001010")),
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std::bitset<13>(std::string("1100111110110")),
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std::bitset<13>(std::string("1001001000101")),
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std::bitset<13>(std::string("0111000100000")),
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std::bitset<13>(std::string("0011001000010")),
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std::bitset<13>(std::string("0010001001110"))};
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// A simple error check
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if ((prn_idx < 0) || (prn_idx > 63))
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{
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return;
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}
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// Assign shifted G2 register based on prn number
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G2_register = G2_register_shifted[prn_idx];
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// Generate G1 and G2 Register
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for (lcv = 0; lcv < _code_length; lcv++)
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{
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G1[lcv] = G1_register[0];
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G2[lcv] = G2_register[0];
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feedback1 = G1_register[0] xor G1_register[9] xor G1_register[10] xor G1_register[12];
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feedback2 = G2_register[0] xor G2_register[1] xor G2_register[3] xor G2_register[4] xor
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G2_register[6] xor G2_register[7] xor G2_register[8] xor G2_register[12];
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for (lcv2 = 0; lcv2 < 12; lcv2++)
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{
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G1_register[lcv2] = G1_register[lcv2 + 1];
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G2_register[lcv2] = G2_register[lcv2 + 1];
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}
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G1_register[12] = feedback1;
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G2_register[12] = feedback2;
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// Reset G1 register if sequence found
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if (G1_register == G1_register_reset)
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{
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G1_register = std::bitset<13>{}.set(); // All true
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}
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}
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delay = _code_length;
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delay += _chip_shift;
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delay %= _code_length;
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// Generate PRN from G1 and G2 Registers
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for (lcv = 0; lcv < _code_length; lcv++)
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{
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aux = G1[(lcv + _chip_shift) % _code_length] xor G2[delay];
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if (aux == true)
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{
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_dest[lcv] = 1;
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}
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else
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{
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_dest[lcv] = -1;
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}
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delay++;
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delay %= _code_length;
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}
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}
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void beidou_b3i_code_gen_float(gsl::span<float> _dest, int32_t _prn, uint32_t _chip_shift)
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{
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const uint32_t _code_length = 10230;
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std::array<int, _code_length> b3i_code_int{};
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beidou_b3i_code_gen_int(b3i_code_int, _prn, _chip_shift);
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for (uint32_t ii = 0; ii < _code_length; ++ii)
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{
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_dest[ii] = static_cast<float>(b3i_code_int[ii]);
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}
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}
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void beidou_b3i_code_gen_complex(gsl::span<std::complex<float>> _dest, int32_t _prn, uint32_t _chip_shift)
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{
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const uint32_t _code_length = 10230;
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std::array<int, _code_length> b3i_code_int{};
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beidou_b3i_code_gen_int(b3i_code_int, _prn, _chip_shift);
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for (uint32_t ii = 0; ii < _code_length; ++ii)
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{
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_dest[ii] = std::complex<float>(static_cast<float>(b3i_code_int[ii]), 0.0F);
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}
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}
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void beidou_b3i_code_gen_complex_sampled(gsl::span<std::complex<float>> _dest, uint32_t _prn, int _fs, uint32_t _chip_shift)
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{
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// This function is based on the GNU software GPS for MATLAB in the Kay Borre book
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std::array<std::complex<float>, 10230> _code{};
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int32_t _samplesPerCode;
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int32_t _codeValueIndex;
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float _ts;
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float _tc;
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float aux;
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const int32_t _codeFreqBasis = 10230000; // Hz
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const int32_t _codeLength = 10230;
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// --- Find number of samples per spreading code ---------------------------
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_samplesPerCode = static_cast<int32_t>(static_cast<double>(_fs) / (static_cast<double>(_codeFreqBasis) / static_cast<double>(_codeLength)));
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// --- Find time constants -------------------------------------------------
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_ts = 1.0 / static_cast<float>(_fs); // Sampling period in sec
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_tc = 1.0 / static_cast<float>(_codeFreqBasis); // C/A chip period in sec
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beidou_b3i_code_gen_complex(_code, _prn, _chip_shift); // generate C/A code 1 sample per chip
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for (int32_t i = 0; i < _samplesPerCode; i++)
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{
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// === Digitizing ==================================================
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// --- Make index array to read C/A code values --------------------
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// The length of the index array depends on the sampling frequency -
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// number of samples per millisecond (because one C/A code period is one
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// millisecond).
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aux = (_ts * (i + 1)) / _tc;
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_codeValueIndex = auxCeil(aux) - 1;
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// --- Make the digitized version of the C/A code ------------------
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// The "upsampled" code is made by selecting values form the CA code
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// chip array (caCode) for the time instances of each sample.
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if (i == _samplesPerCode - 1)
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{
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// --- Correct the last index (due to number rounding issues) -----------
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_dest[i] = _code[_codeLength - 1];
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}
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else
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{
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_dest[i] = _code[_codeValueIndex]; // repeat the chip -> upsample
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}
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}
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}
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