mirror of https://github.com/gnss-sdr/gnss-sdr
132 lines
4.5 KiB
C++
132 lines
4.5 KiB
C++
/*!
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* \file gps_l2c_signal.cc
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* \brief This class implements signal generators for the GPS L2C signals
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* \author Javier Arribas, 2015. jarribas(at)cttc.es
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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) 2010-2018 (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 "gps_l2c_signal.h"
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#include "GPS_L2C.h"
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#include <cmath>
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#include <memory>
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int32_t gps_l2c_m_shift(int32_t x)
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{
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return static_cast<int32_t>((x >> 1) ^ ((x & 1) * 0445112474));
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}
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void gps_l2c_m_code(gsl::span<int32_t> _dest, uint32_t _prn)
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{
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int32_t x;
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x = GPS_L2C_M_INIT_REG[_prn - 1];
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for (int32_t n = 0; n < GPS_L2_M_CODE_LENGTH_CHIPS; n++)
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{
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_dest[n] = static_cast<int8_t>(x & 1);
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x = gps_l2c_m_shift(x);
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}
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}
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void gps_l2c_m_code_gen_complex(gsl::span<std::complex<float>> _dest, uint32_t _prn)
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{
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std::unique_ptr<int32_t> _code{new int32_t[GPS_L2_M_CODE_LENGTH_CHIPS]};
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gsl::span<int32_t> _code_span(_code, GPS_L2_M_CODE_LENGTH_CHIPS);
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if (_prn > 0 and _prn < 51)
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{
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gps_l2c_m_code(_code_span, _prn);
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}
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for (int32_t i = 0; i < GPS_L2_M_CODE_LENGTH_CHIPS; i++)
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{
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_dest[i] = std::complex<float>(1.0 - 2.0 * _code_span[i], 0.0);
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}
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}
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void gps_l2c_m_code_gen_float(gsl::span<float> _dest, uint32_t _prn)
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{
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std::unique_ptr<int32_t> _code{new int32_t[GPS_L2_M_CODE_LENGTH_CHIPS]};
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gsl::span<int32_t> _code_span(_code, GPS_L2_M_CODE_LENGTH_CHIPS);
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if (_prn > 0 and _prn < 51)
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{
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gps_l2c_m_code(_code_span, _prn);
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}
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for (int32_t i = 0; i < GPS_L2_M_CODE_LENGTH_CHIPS; i++)
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{
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_dest[i] = 1.0 - 2.0 * static_cast<float>(_code_span[i]);
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}
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}
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/*
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* Generates complex GPS L2C M code for the desired SV ID and sampled to specific sampling frequency
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*/
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void gps_l2c_m_code_gen_complex_sampled(gsl::span<std::complex<float>> _dest, uint32_t _prn, int32_t _fs)
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{
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std::unique_ptr<int32_t> _code{new int32_t[GPS_L2_M_CODE_LENGTH_CHIPS]};
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gsl::span<int32_t> _code_span(_code, GPS_L2_M_CODE_LENGTH_CHIPS);
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if (_prn > 0 and _prn < 51)
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{
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gps_l2c_m_code(_code_span, _prn);
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}
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int32_t _samplesPerCode, _codeValueIndex;
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float _ts;
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float _tc;
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const int32_t _codeLength = GPS_L2_M_CODE_LENGTH_CHIPS;
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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>(GPS_L2_M_CODE_RATE_HZ) / 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>(GPS_L2_M_CODE_RATE_HZ); // C/A chip period in sec
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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 L2C code values -------------------------
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_codeValueIndex = std::ceil((_ts * (static_cast<float>(i) + 1)) / _tc) - 1;
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//--- Make the digitized version of the L2C code -----------------------
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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] = std::complex<float>(1.0 - 2.0 * _code_span[_codeLength - 1], 0);
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}
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else
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{
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_dest[i] = std::complex<float>(1.0 - 2.0 * _code_span[_codeValueIndex], 0); //repeat the chip -> upsample
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}
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}
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}
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