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"

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

void beidou_b3i_code_gen_int(int* _dest, signed int _prn, unsigned int _chip_shift)
{
    const unsigned int _code_length = 10230;
    int8_t G1[_code_length];
    int8_t G2[_code_length];
    std::array<int8_t,13> G1_register = {{-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1}};
    std::array<int8_t,13> G2_register = {{-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1}};
    std::array<int8_t,13> G1_register_reset =  {{-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,1,1}};
    int8_t feedback1, feedback2;
    uint32_t lcv, lcv2;
    int32_t prn_idx = _prn - 1;

    std::array<std::array<int8_t, 13>, 63> G2_register_shifted = {{
    		 {{-1,1,-1,1,-1,-1,-1,-1,-1,-1,-1,-1,-1}}, {{-1,-1,-1,-1,1,1,1,-1,1,-1,1,-1,-1}},
    		 {{-1,1,-1,-1,-1,-1,1,1,1,-1,1,-1,1}},    {{-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,1,-1,-1}},
    		 {{-1,-1,1,1,-1,1,1,1,-1,-1,-1,-1,-1}},   {{-1,1,1,-1,1,1,-1,-1,1,1,-1,1,1}},
    		 {{-1,-1,-1,-1,-1,-1,-1,1,-1,1,1,-1,1}},  {{-1,-1,-1,1,-1,-1,-1,-1,-1,-1,-1,1,-1}},
    		 {{-1,1,-1,1,1,1,1,1,1,1,1,-1,1}},        {{1,1,-1,1,1,1,1,1,-1,-1,1,-1,-1}},
    		 {{-1,-1,-1,1,-1,1,-1,-1,-1,1,1,1,1}},    {{1,1,-1,1,-1,-1,1,1,-1,-1,-1,-1,1}},
    		 {{1,-1,-1,1,1,-1,1,1,-1,1,-1,1,-1}},     {{1,-1,-1,-1,1,1,1,-1,1,1,-1,-1,1}},
    		 {{-1,1,1,1,-1,-1,1,1,1,-1,1,1,-1}},      {{-1,-1,-1,1,1,1,-1,-1,-1,-1,-1,1,1}},
    		 {{1,1,-1,1,1,-1,-1,1,1,1,-1,1,-1}},      {{1,1,1,1,1,-1,-1,-1,1,-1,-1,1,1}},
    		 {{-1,1,1,1,-1,1,-1,1,-1,1,-1,-1,-1}},    {{1,1,1,-1,1,-1,-1,1,-1,-1,-1,-1,1}},
    		 {{1,1,-1,1,1,1,1,-1,1,-1,-1,1,-1}},      {{1,1,-1,1,-1,-1,1,1,1,-1,1,-1,1}},
    		 {{1,1,1,-1,1,-1,-1,1,1,-1,-1,-1,-1}},    {{1,1,-1,-1,1,1,-1,-1,1,1,1,-1,1}},
    		 {{1,1,-1,-1,-1,1,-1,1,1,-1,1,1,1}},      {{1,-1,1,1,-1,1,1,-1,1,-1,1,1,-1}},
    		 {{-1,1,-1,-1,1,-1,-1,1,-1,1,1,-1,-1}},   {{-1,1,-1,1,-1,-1,-1,-1,1,1,1,-1,1}},
    		 {{1,1,1,-1,1,-1,-1,-1,-1,1,-1,1,-1}},    {{1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1}},
    		 {{1,-1,-1,1,-1,-1,1,1,1,-1,-1,-1,-1}},   {{-1,1,-1,1,-1,-1,1,1,1,-1,1,1,-1}},
    		 {{-1,1,1,-1,1,-1,1,-1,1,-1,1,-1,-1}},    {{-1,-1,1,1,-1,-1,1,-1,1,1,-1,1,-1}},
    		 {{-1,-1,1,-1,1,1,-1,1,-1,-1,-1,1,-1}},   {{-1,-1,-1,-1,-1,1,-1,-1,-1,1,-1,1,1}},
    		 {{1,1,-1,1,-1,1,-1,-1,1,1,-1,-1,-1}},    {{-1,-1,-1,1,-1,1,1,1,-1,1,1,1,1}},
    		 {{-1,-1,1,-1,-1,-1,1,1,-1,1,1,1,1}},     {{-1,-1,1,-1,1,-1,-1,1,1,-1,-1,-1,1}},
    		 {{-1,1,1,1,1,1,1,-1,-1,1,-1,1,1}},       {{1,-1,1,-1,-1,-1,-1,1,-1,-1,1,1,-1}},
    		 {{1,-1,-1,1,-1,-1,1,-1,-1,-1,-1,1,1}},   {{-1,-1,1,-1,1,1,-1,-1,-1,1,1,1,-1}},
    		 {{1,1,-1,-1,-1,1,1,-1,1,1,1,-1,1}},      {{1,-1,1,-1,1,-1,-1,1,1,1,-1,1,-1}},
    		 {{-1,1,1,-1,-1,-1,-1,-1,1,1,-1,-1,1}},   {{-1,-1,-1,-1,-1,1,-1,1,1,-1,1,1,1}},
    		 {{1,1,1,1,-1,1,-1,1,1,-1,1,1,-1}},       {{-1,1,1,1,1,-1,1,-1,1,-1,-1,1,1}},
    		 {{-1,-1,-1,-1,1,1,-1,1,1,-1,-1,1,1}},    {{1,-1,1,1,-1,-1,1,1,1,-1,-1,-1,-1}},
    		 {{1,1,1,1,1,1,1,1,-1,-1,1,1,1}},         {{-1,1,1,1,1,1,1,1,1,1,-1,1,1}},
    		 {{1,1,-1,-1,1,-1,1,-1,1,1,-1,-1,1}},     {{-1,1,-1,-1,1,1,-1,1,1,1,-1,-1,1}},
    		 {{1,-1,-1,-1,1,1,-1,-1,-1,-1,1,1,1}},    {{1,1,-1,1,-1,-1,-1,1,1,-1,1,-1,1}},
    		 {{-1,-1,1,1,-1,-1,-1,-1,-1,1,-1,-1,1}},  {{-1,1,1,-1,1,1,-1,1,1,1,-1,1,-1}},
    		 {{1,-1,-1,-1,1,1,1,-1,1,1,1,1,1}},       {{1,1,-1,-1,1,1,-1,1,1,1,1,-1,1}},
    		 {{1,1,-1,1,1,1,-1,1,1,-1,-1,-1,1}}}};

    /* A simple error check */
    if ((prn_idx < 0) || (prn_idx > 64))
        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[12];
    		G2[lcv]   = G2_register[12];

    		feedback1 = G1_register[0]*G1_register[2]*G1_register[3]*G1_register[12];
    		feedback2 = G2_register[0]*G2_register[4]*G2_register[5]*G2_register[6]*
    				    G2_register[8]*G2_register[9]*G2_register[11]*G2_register[12];

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

    		G1_register[0] = feedback1;
    		G2_register[0] = feedback2;

    		// Reset G1 register if sequence found
    		if(G1_register == G1_register_reset)
				{
    				G1_register = {{-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1}};
				}

			// Generate ranging code
    		_dest[lcv] = static_cast<int>(-G1[lcv]*G2[lcv]);
    	}
}


void beidou_b3i_code_gen_float(float* _dest, signed int _prn, unsigned int _chip_shift)
{
    unsigned int _code_length = 10230;
    int b3i_code_int[10230];

    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(std::complex<float>* _dest, signed int _prn, unsigned int _chip_shift)
{
    unsigned int _code_length = 10230;
    int b3i_code_int[10230];

    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(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::complex<float> _code[10230];
    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
                }
        }
}