gnss-sdr/src/algorithms/libs/beidou_b3i_signal_processing.cc

/*!
 * \file beidou_b3i_signal_processing.cc
 * \brief This class implements various functions for BeiDou B1I signal
 * \author Damian Miralles, 2019. dmiralles2009@gmail.com
 *
 * Detailed description of the file here if needed.
 *
 * -------------------------------------------------------------------------
 *
 * 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 "beidou_b3i_signal_processing.h"
#include <array>
#include <bitset>
#include <string>

auto auxCeil = [](float x) { return static_cast<int>(static_cast<long>((x) + 1)); };

void beidou_b3i_code_gen_int(gsl::span<int> _dest, signed int _prn, unsigned int _chip_shift)
{
    const unsigned int _code_length = 10230;
    std::bitset<_code_length> G1{};
    std::bitset<_code_length> G2{};
    auto G1_register = std::move(std::bitset<13>{}.set());  // All true
    auto G2_register = std::move(std::bitset<13>{}.set());  // All true
    auto G1_register_reset = std::move(std::bitset<13>{}.set());
    G1_register_reset.reset(0);
    G1_register_reset.reset(1);  // {false, false, true, true, true, true, true, true, true, true, true, true, true};

    bool feedback1, feedback2, aux;
    uint32_t lcv, lcv2, delay;
    int32_t prn_idx = _prn - 1;

    const std::array<std::bitset<13>, 63> G2_register_shifted =
        {std::bitset<13>(std::string("1010111111111")),
            std::bitset<13>(std::string("1111000101011")),
            std::bitset<13>(std::string("1011110001010")),
            std::bitset<13>(std::string("1111111111011")),
            std::bitset<13>(std::string("1100100011111")),
            std::bitset<13>(std::string("1001001100100")),
            std::bitset<13>(std::string("1111111010010")),
            std::bitset<13>(std::string("1110111111101")),
            std::bitset<13>(std::string("1010000000010")),
            std::bitset<13>(std::string("0010000011011")),
            std::bitset<13>(std::string("1110101110000")),
            std::bitset<13>(std::string("0010110011110")),
            std::bitset<13>(std::string("0110010010101")),
            std::bitset<13>(std::string("0111000100110")),
            std::bitset<13>(std::string("1000110001001")),
            std::bitset<13>(std::string("1110001111100")),
            std::bitset<13>(std::string("0010011000101")),
            std::bitset<13>(std::string("0000011101100")),
            std::bitset<13>(std::string("1000101010111")),
            std::bitset<13>(std::string("0001011011110")),
            std::bitset<13>(std::string("0010000101101")),
            std::bitset<13>(std::string("0010110001010")),
            std::bitset<13>(std::string("0001011001111")),
            std::bitset<13>(std::string("0011001100010")),
            std::bitset<13>(std::string("0011101001000")),
            std::bitset<13>(std::string("0100100101001")),
            std::bitset<13>(std::string("1011011010011")),
            std::bitset<13>(std::string("1010111100010")),
            std::bitset<13>(std::string("0001011110101")),
            std::bitset<13>(std::string("0111111111111")),
            std::bitset<13>(std::string("0110110001111")),
            std::bitset<13>(std::string("1010110001001")),
            std::bitset<13>(std::string("1001010101011")),
            std::bitset<13>(std::string("1100110100101")),
            std::bitset<13>(std::string("1101001011101")),
            std::bitset<13>(std::string("1111101110100")),
            std::bitset<13>(std::string("0010101100111")),
            std::bitset<13>(std::string("1110100010000")),
            std::bitset<13>(std::string("1101110010000")),
            std::bitset<13>(std::string("1101011001110")),
            std::bitset<13>(std::string("1000000110100")),
            std::bitset<13>(std::string("0101111011001")),
            std::bitset<13>(std::string("0110110111100")),
            std::bitset<13>(std::string("1101001110001")),
            std::bitset<13>(std::string("0011100100010")),
            std::bitset<13>(std::string("0101011000101")),
            std::bitset<13>(std::string("1001111100110")),
            std::bitset<13>(std::string("1111101001000")),
            std::bitset<13>(std::string("0000101001001")),
            std::bitset<13>(std::string("1000010101100")),
            std::bitset<13>(std::string("1111001001100")),
            std::bitset<13>(std::string("0100110001111")),
            std::bitset<13>(std::string("0000000011000")),
            std::bitset<13>(std::string("1000000000100")),
            std::bitset<13>(std::string("0011010100110")),
            std::bitset<13>(std::string("1011001000110")),
            std::bitset<13>(std::string("0111001111000")),
            std::bitset<13>(std::string("0010111001010")),
            std::bitset<13>(std::string("1100111110110")),
            std::bitset<13>(std::string("1001001000101")),
            std::bitset<13>(std::string("0111000100000")),
            std::bitset<13>(std::string("0011001000010")),
            std::bitset<13>(std::string("0010001001110"))};

    // A simple error check
    if ((prn_idx < 0) || (prn_idx > 63))
        {
            return;
        }

    // Assign shifted G2 register based on prn number
    G2_register = G2_register_shifted[prn_idx];

    // Generate G1 and G2 Register
    for (lcv = 0; lcv < _code_length; lcv++)
        {
            G1[lcv] = G1_register[0];
            G2[lcv] = G2_register[0];

            feedback1 = G1_register[0] xor G1_register[9] xor G1_register[10] xor G1_register[12];
            feedback2 = G2_register[0] xor G2_register[1] xor G2_register[3] xor G2_register[4] xor
                        G2_register[6] xor G2_register[7] xor G2_register[8] xor G2_register[12];

            for (lcv2 = 0; lcv2 < 12; lcv2++)
                {
                    G1_register[lcv2] = G1_register[lcv2 + 1];
                    G2_register[lcv2] = G2_register[lcv2 + 1];
                }

            G1_register[12] = feedback1;
            G2_register[12] = feedback2;

            // Reset G1 register if sequence found
            if (G1_register == G1_register_reset)
                {
                    G1_register = std::move(std::bitset<13>{}.set());  // All true
                }
        }

    delay = _code_length;
    delay += _chip_shift;
    delay %= _code_length;

    // Generate PRN from G1 and G2 Registers
    for (lcv = 0; lcv < _code_length; lcv++)
        {
            aux = G1[(lcv + _chip_shift) % _code_length] xor G2[delay];
            if (aux == true)
                {
                    _dest[lcv] = 1;
                }
            else
                {
                    _dest[lcv] = -1;
                }

            delay++;
            delay %= _code_length;
        }
}


void beidou_b3i_code_gen_float(gsl::span<float> _dest, signed int _prn, unsigned int _chip_shift)
{
    const unsigned int _code_length = 10230;
    std::array<int, _code_length> b3i_code_int{};

    beidou_b3i_code_gen_int(b3i_code_int, _prn, _chip_shift);

    for (unsigned int ii = 0; ii < _code_length; ++ii)
        {
            _dest[ii] = static_cast<float>(b3i_code_int[ii]);
        }
}


void beidou_b3i_code_gen_complex(gsl::span<std::complex<float>> _dest, signed int _prn, unsigned int _chip_shift)
{
    const unsigned int _code_length = 10230;
    std::array<int, _code_length> b3i_code_int{};

    beidou_b3i_code_gen_int(b3i_code_int, _prn, _chip_shift);

    for (unsigned int ii = 0; ii < _code_length; ++ii)
        {
            _dest[ii] = std::complex<float>(static_cast<float>(b3i_code_int[ii]), 0.0F);
        }
}


void beidou_b3i_code_gen_complex_sampled(gsl::span<std::complex<float>> _dest, unsigned int _prn, int _fs, unsigned int _chip_shift)
{
    // This function is based on the GNU software GPS for MATLAB in the Kay Borre book
    std::array<std::complex<float>, 10230> _code{};
    signed int _samplesPerCode, _codeValueIndex;
    float _ts;
    float _tc;
    float aux;
    const signed int _codeFreqBasis = 10230000;  // Hz
    const signed int _codeLength = 10230;

    //--- Find number of samples per spreading code ----------------------------
    _samplesPerCode = static_cast<signed int>(static_cast<double>(_fs) / static_cast<double>(_codeFreqBasis / _codeLength));

    //--- Find time constants --------------------------------------------------
    _ts = 1.0 / static_cast<float>(_fs);                    // Sampling period in sec
    _tc = 1.0 / static_cast<float>(_codeFreqBasis);         // C/A chip period in sec
    beidou_b3i_code_gen_complex(_code, _prn, _chip_shift);  // generate C/A code 1 sample per chip

    for (signed int i = 0; i < _samplesPerCode; i++)
        {
            //=== Digitizing =======================================================

            //--- Make index array to read C/A code values -------------------------
            // The length of the index array depends on the sampling frequency -
            // number of samples per millisecond (because one C/A code period is one
            // millisecond).

            // _codeValueIndex = ceil((_ts * ((float)i + 1)) / _tc) - 1;
            aux = (_ts * (i + 1)) / _tc;
            _codeValueIndex = auxCeil(aux) - 1;

            //--- Make the digitized version of the C/A code -----------------------
            // The "upsampled" code is made by selecting values form the CA code
            // chip array (caCode) for the time instances of each sample.
            if (i == _samplesPerCode - 1)
                {
                    //--- Correct the last index (due to number rounding issues) -----------
                    _dest[i] = _code[_codeLength - 1];
                }
            else
                {
                    _dest[i] = _code[_codeValueIndex];  //repeat the chip -> upsample
                }
        }
}