gnss-sdr/src/algorithms/libs/gps_l2c_signal.cc

126 lines
4.1 KiB
C++

/*!
* \file gps_l2c_signal.cc
* \brief This class implements signal generators for the GPS L2C signals
* \author Javier Arribas, 2015. jarribas(at)cttc.es
*
* 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 "gps_l2c_signal.h"
#include "GPS_L2C.h"
#include <cstdint>
#include <cmath>
int32_t gps_l2c_m_shift(int32_t x)
{
return static_cast<int32_t>((x >> 1)^((x & 1) * 0445112474));
}
void gps_l2c_m_code(int32_t * _dest, unsigned int _prn)
{
int32_t x;
x = GPS_L2C_M_INIT_REG[ _prn - 1];
for (int n = 0; n < GPS_L2_M_CODE_LENGTH_CHIPS; n++)
{
_dest[n] = static_cast<int8_t>(x&1);
x = gps_l2c_m_shift(x);
}
}
void gps_l2c_m_code_gen_complex(std::complex<float>* _dest, unsigned int _prn)
{
int32_t* _code = new int32_t[GPS_L2_M_CODE_LENGTH_CHIPS];
if (_prn > 0 and _prn < 51)
{
gps_l2c_m_code(_code, _prn);
}
for (signed int i = 0; i < GPS_L2_M_CODE_LENGTH_CHIPS; i++)
{
_dest[i] = std::complex<float>(1.0 - 2.0 * _code[i], 0.0);
}
delete[] _code;
}
/*
* Generates complex GPS L2C M code for the desired SV ID and sampled to specific sampling frequency
*/
void gps_l2c_m_code_gen_complex_sampled(std::complex<float>* _dest, unsigned int _prn, signed int _fs)
{
int32_t* _code = new int32_t[GPS_L2_M_CODE_LENGTH_CHIPS];
if (_prn > 0 and _prn < 51)
{
gps_l2c_m_code(_code, _prn);
}
signed int _samplesPerCode, _codeValueIndex;
float _ts;
float _tc;
const signed int _codeLength = GPS_L2_M_CODE_LENGTH_CHIPS;
//--- Find number of samples per spreading code ----------------------------
_samplesPerCode = static_cast<int>(static_cast<double>(_fs) / (static_cast<double>(GPS_L2_M_CODE_RATE_HZ) / static_cast<double>(_codeLength)));
//--- Find time constants --------------------------------------------------
_ts = 1.0 / static_cast<float>(_fs); // Sampling period in sec
_tc = 1.0 / static_cast<float>(GPS_L2_M_CODE_RATE_HZ); // C/A chip period in sec
//float aux;
for (signed int i = 0; i < _samplesPerCode; i++)
{
//=== Digitizing =======================================================
//--- Make index array to read L2C code values -------------------------
//TODO: Check this formula! Seems to start with an extra sample
_codeValueIndex = ceil((_ts * (static_cast<float>(i) + 1)) / _tc) - 1;
//aux = (_ts * (i + 1)) / _tc;
//_codeValueIndex = static_cast<int>(static_cast<long>(aux)) - 1;
//--- Make the digitized version of the L2C code -----------------------
if (i == _samplesPerCode - 1)
{
//--- Correct the last index (due to number rounding issues) -----------
_dest[i] = std::complex<float>(1.0 - 2.0 * _code[_codeLength - 1], 0);
}
else
{
_dest[i] = std::complex<float>(1.0 - 2.0 * _code[_codeValueIndex], 0); //repeat the chip -> upsample
}
}
delete[] _code;
}