mirror of
https://github.com/gnss-sdr/gnss-sdr
synced 2024-11-17 15:24:56 +00:00
135 lines
4.4 KiB
C++
135 lines
4.4 KiB
C++
/*!
|
|
* \file glonass_l2_signal_replica.cc
|
|
* \brief This file implements various functions for GLONASS L2 CA signal
|
|
* replica generation
|
|
* \author Damian Miralles, 2018, dmiralles2009(at)gmail.com
|
|
*
|
|
*
|
|
* -----------------------------------------------------------------------------
|
|
*
|
|
* Copyright (C) 2010-2020 (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.
|
|
*
|
|
* SPDX-License-Identifier: GPL-3.0-or-later
|
|
*
|
|
* -----------------------------------------------------------------------------
|
|
*/
|
|
|
|
#include "glonass_l2_signal_replica.h"
|
|
#include <array>
|
|
#include <bitset>
|
|
|
|
const auto AUX_CEIL = [](float x) { return static_cast<int32_t>(static_cast<int64_t>((x) + 1)); };
|
|
|
|
void glonass_l2_ca_code_gen_complex(own::span<std::complex<float>> _dest, uint32_t _chip_shift)
|
|
{
|
|
const uint32_t _code_length = 511;
|
|
std::bitset<_code_length> G1{};
|
|
auto G1_register = std::bitset<9>{}.set(); // All true
|
|
bool feedback1;
|
|
bool aux;
|
|
uint32_t delay;
|
|
uint32_t lcv;
|
|
uint32_t lcv2;
|
|
|
|
/* Generate G1 Register */
|
|
for (lcv = 0; lcv < _code_length; lcv++)
|
|
{
|
|
G1[lcv] = G1_register[2];
|
|
|
|
feedback1 = G1_register[4] xor G1_register[0];
|
|
|
|
for (lcv2 = 0; lcv2 < 8; lcv2++)
|
|
{
|
|
G1_register[lcv2] = G1_register[lcv2 + 1];
|
|
}
|
|
|
|
G1_register[8] = feedback1;
|
|
}
|
|
|
|
/* Generate PRN from G1 Register */
|
|
for (lcv = 0; lcv < _code_length; lcv++)
|
|
{
|
|
aux = G1[lcv];
|
|
if (aux == true)
|
|
{
|
|
_dest[lcv] = std::complex<float>(1, 0);
|
|
}
|
|
else
|
|
{
|
|
_dest[lcv] = std::complex<float>(-1, 0);
|
|
}
|
|
}
|
|
|
|
/* Set the delay */
|
|
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];
|
|
if (aux == true)
|
|
{
|
|
_dest[lcv] = std::complex<float>(1, 0);
|
|
}
|
|
else
|
|
{
|
|
_dest[lcv] = std::complex<float>(-1, 0);
|
|
}
|
|
delay++;
|
|
delay %= _code_length;
|
|
}
|
|
}
|
|
|
|
|
|
/*
|
|
* Generates complex GLONASS L2 C/A code for the desired SV ID and sampled to specific sampling frequency
|
|
*/
|
|
void glonass_l2_ca_code_gen_complex_sampled(own::span<std::complex<float>> _dest, int32_t _fs, uint32_t _chip_shift)
|
|
{
|
|
constexpr int32_t _codeFreqBasis = 511000; // Hz
|
|
constexpr int32_t _codeLength = 511;
|
|
constexpr float _tc = 1.0 / static_cast<float>(_codeFreqBasis); // C/A chip period in sec
|
|
|
|
const auto _samplesPerCode = static_cast<int32_t>(static_cast<double>(_fs) / (static_cast<double>(_codeFreqBasis) / static_cast<double>(_codeLength)));
|
|
const float _ts = 1.0F / static_cast<float>(_fs); // Sampling period in sec
|
|
|
|
std::array<std::complex<float>, 511> _code{};
|
|
int32_t _codeValueIndex;
|
|
float aux;
|
|
|
|
glonass_l2_ca_code_gen_complex(_code, _chip_shift); // generate C/A code 1 sample per chip
|
|
|
|
for (int32_t 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).
|
|
|
|
aux = (_ts * (static_cast<float>(i) + 1)) / _tc;
|
|
_codeValueIndex = AUX_CEIL(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
|
|
}
|
|
}
|
|
}
|