mirror of https://github.com/gnss-sdr/gnss-sdr
124 lines
4.2 KiB
C++
124 lines
4.2 KiB
C++
/*!
|
|
* \file glonass_l1_signal_replica.cc
|
|
* \brief This file implements various functions for GLONASS L1 CA signal
|
|
* replica generation
|
|
* \author Gabriel Araujo, 2017. gabriel.araujo(at)ieee.org
|
|
*
|
|
*
|
|
* -----------------------------------------------------------------------------
|
|
*
|
|
* GNSS-SDR is a Global Navigation Satellite System software-defined receiver.
|
|
* This file is part of GNSS-SDR.
|
|
*
|
|
* Copyright (C) 2010-2020 (see AUTHORS file for a list of contributors)
|
|
* SPDX-License-Identifier: GPL-3.0-or-later
|
|
*
|
|
* -----------------------------------------------------------------------------
|
|
*/
|
|
|
|
#include "glonass_l1_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_l1_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
|
|
uint32_t lcv;
|
|
uint32_t lcv2;
|
|
bool feedback1;
|
|
bool aux;
|
|
|
|
/* Generate G1 Register */
|
|
for (lcv = 0; lcv < code_length; lcv++)
|
|
{
|
|
G1[lcv] = G1_register[2];
|
|
|
|
feedback1 = G1_register[4] ^ 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);
|
|
}
|
|
}
|
|
|
|
/* 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);
|
|
}
|
|
}
|
|
}
|
|
|
|
|
|
/*
|
|
* Generates complex GLONASS L1 C/A code for the desired SV ID and sampled to specific sampling frequency
|
|
*/
|
|
void glonass_l1_ca_code_gen_complex_sampled(own::span<std::complex<float>> dest, int32_t sampling_freq, uint32_t chip_shift)
|
|
{
|
|
constexpr int32_t codeFreqBasis = 511000; // chips per second
|
|
constexpr int32_t codeLength = 511;
|
|
constexpr float tc = 1.0 / static_cast<float>(codeFreqBasis); // C/A chip period in sec
|
|
|
|
const float ts = 1.0F / static_cast<float>(sampling_freq); // Sampling period in sec
|
|
const auto samplesPerCode = static_cast<int32_t>(static_cast<double>(sampling_freq) / (static_cast<double>(codeFreqBasis) / static_cast<double>(codeLength)));
|
|
|
|
std::array<std::complex<float>, 511> code_aux{};
|
|
int32_t codeValueIndex;
|
|
float aux;
|
|
|
|
glonass_l1_ca_code_gen_complex(code_aux, 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_aux[codeLength - 1];
|
|
}
|
|
else
|
|
{
|
|
dest[i] = code_aux[codeValueIndex]; // repeat the chip -> upsample
|
|
}
|
|
}
|
|
}
|