mirror of
https://github.com/gnss-sdr/gnss-sdr
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109 lines
3.4 KiB
C++
109 lines
3.4 KiB
C++
/*!
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* \file gps_l2c_signal_replica.cc
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* \brief This file implements signal generators for GPS L2C signals
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* \author Javier Arribas, 2015. jarribas(at)cttc.es
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*
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*
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* -----------------------------------------------------------------------------
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*
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* GNSS-SDR is a Global Navigation Satellite System software-defined receiver.
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* This file is part of GNSS-SDR.
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*
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* Copyright (C) 2010-2020 (see AUTHORS file for a list of contributors)
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* SPDX-License-Identifier: GPL-3.0-or-later
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*
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* -----------------------------------------------------------------------------
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*/
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#include "gps_l2c_signal_replica.h"
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#include "GPS_L2C.h"
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#include <array>
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#include <cmath>
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#include <memory>
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uint32_t gps_l2c_m_shift(uint32_t x)
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{
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return ((x >> 1U) xor ((x & 1U) * 0445112474U));
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}
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void gps_l2c_m_code(own::span<int32_t> dest, uint32_t prn)
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{
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uint32_t 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<int32_t>(x & 1U);
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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(own::span<std::complex<float>> dest, uint32_t prn)
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{
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std::array<int32_t, GPS_L2_M_CODE_LENGTH_CHIPS> code_aux{};
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if (prn > 0 and prn < 51)
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{
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gps_l2c_m_code(code_aux, 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>(0.0, 1.0F - 2.0F * code_aux[i]);
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}
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}
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void gps_l2c_m_code_gen_float(own::span<float> dest, uint32_t prn)
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{
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std::array<int32_t, GPS_L2_M_CODE_LENGTH_CHIPS> code_aux{};
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if (prn > 0 and prn < 51)
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{
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gps_l2c_m_code(code_aux, 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_aux[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(own::span<std::complex<float>> dest, uint32_t prn, int32_t sampling_freq)
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{
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constexpr int32_t codeLength = GPS_L2_M_CODE_LENGTH_CHIPS;
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constexpr float tc = 1.0F / static_cast<float>(GPS_L2_M_CODE_RATE_CPS); // L2C chip period in sec
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const auto samplesPerCode = static_cast<int32_t>(static_cast<double>(sampling_freq) / (static_cast<double>(GPS_L2_M_CODE_RATE_CPS) / static_cast<double>(codeLength)));
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const float ts = 1.0F / static_cast<float>(sampling_freq); // Sampling period in sec
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int32_t codeValueIndex;
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std::array<int32_t, GPS_L2_M_CODE_LENGTH_CHIPS> code_aux{};
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if (prn > 0 and prn < 51)
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{
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gps_l2c_m_code(code_aux, prn);
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}
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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) + 1.0F)) / 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>(0.0, 1.0F - 2.0F * code_aux[codeLength - 1]);
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}
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else
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{
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dest[i] = std::complex<float>(0.0, 1.0F - 2.0F * code_aux[codeValueIndex]); // repeat the chip -> upsample
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}
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}
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}
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