mirror of https://github.com/gnss-sdr/gnss-sdr
299 lines
9.5 KiB
C++
299 lines
9.5 KiB
C++
/*!
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* \file gps_l5_signal_replica.cc
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* \brief This file implements signal generators for GPS L5 signals
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* \author Javier Arribas, 2017. 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_l5_signal_replica.h"
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#include "GPS_L5.h"
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#include <array>
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#include <cmath>
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#include <deque>
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std::deque<bool> l5i_xa_shift(const std::deque<bool>& xa) // GPS-IS-705E Figure 3-4 pp. 15
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{
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if (xa == std::deque<bool>{true, true, true, true, true, true, true, true, true, true, true, false, true})
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{
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return std::deque<bool>{true, true, true, true, true, true, true, true, true, true, true, true, true};
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}
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std::deque<bool> out(xa.cbegin(), xa.cend() - 1);
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out.push_front(xa[12] xor xa[11] xor xa[9] xor xa[8]);
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return out;
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}
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std::deque<bool> l5q_xa_shift(const std::deque<bool>& xa)
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{
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if (xa == std::deque<bool>{true, true, true, true, true, true, true, true, true, true, true, false, true})
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{
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return std::deque<bool>{true, true, true, true, true, true, true, true, true, true, true, true, true};
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}
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std::deque<bool> out(xa.cbegin(), xa.cend() - 1);
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out.push_front(xa[12] xor xa[11] xor xa[9] xor xa[8]);
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return out;
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}
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std::deque<bool> l5i_xb_shift(const std::deque<bool>& xb) // GPS-IS-705E Figure 3-5 pp. 16
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{
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std::deque<bool> out(xb.cbegin(), xb.cend() - 1);
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out.push_front(xb[12] xor xb[11] xor xb[7] xor xb[6] xor xb[5] xor xb[3] xor xb[2] xor xb[0]);
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return out;
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}
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std::deque<bool> l5q_xb_shift(const std::deque<bool>& xb)
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{
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std::deque<bool> out(xb.cbegin(), xb.cend() - 1);
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out.push_front(xb[12] xor xb[11] xor xb[7] xor xb[6] xor xb[5] xor xb[3] xor xb[2] xor xb[0]);
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return out;
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}
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std::deque<bool> make_l5i_xa()
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{
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std::deque<bool> xa = {true, true, true, true, true, true, true, true, true, true, true, true, true};
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std::deque<bool> y(GPS_L5I_CODE_LENGTH_CHIPS, false);
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for (int32_t i = 0; i < GPS_L5I_CODE_LENGTH_CHIPS; i++)
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{
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y[i] = xa[12];
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xa = l5i_xa_shift(xa);
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}
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return y;
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}
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std::deque<bool> make_l5i_xb()
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{
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std::deque<bool> xb = {true, true, true, true, true, true, true, true, true, true, true, true, true};
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std::deque<bool> y(GPS_L5I_CODE_LENGTH_CHIPS, false);
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for (int32_t i = 0; i < GPS_L5I_CODE_LENGTH_CHIPS; i++)
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{
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y[i] = xb[12];
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xb = l5i_xb_shift(xb);
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}
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return y;
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}
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std::deque<bool> make_l5q_xa()
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{
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std::deque<bool> xa = {true, true, true, true, true, true, true, true, true, true, true, true, true};
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std::deque<bool> y(GPS_L5Q_CODE_LENGTH_CHIPS, false);
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for (int32_t i = 0; i < GPS_L5Q_CODE_LENGTH_CHIPS; i++)
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{
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y[i] = xa[12];
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xa = l5q_xa_shift(xa);
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}
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return y;
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}
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std::deque<bool> make_l5q_xb()
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{
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std::deque<bool> xb = {true, true, true, true, true, true, true, true, true, true, true, true, true};
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std::deque<bool> y(GPS_L5Q_CODE_LENGTH_CHIPS, false);
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for (int32_t i = 0; i < GPS_L5Q_CODE_LENGTH_CHIPS; i++)
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{
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y[i] = xb[12];
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xb = l5q_xb_shift(xb);
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}
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return y;
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}
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void make_l5i(own::span<int32_t> dest, int32_t prn)
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{
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const int32_t xb_offset = GPS_L5I_INIT_REG[prn];
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const std::deque<bool> xb = make_l5i_xb();
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const std::deque<bool> xa = make_l5i_xa();
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std::deque<bool> xb_shift(GPS_L5I_CODE_LENGTH_CHIPS, false);
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for (int32_t n = 0; n < GPS_L5I_CODE_LENGTH_CHIPS; n++)
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{
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xb_shift[n] = xb[(xb_offset + n) % GPS_L5I_CODE_LENGTH_CHIPS];
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}
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for (int32_t n = 0; n < GPS_L5I_CODE_LENGTH_CHIPS; n++)
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{
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dest[n] = xa[n] xor xb_shift[n];
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}
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}
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void make_l5q(own::span<int32_t> dest, int32_t prn)
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{
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const int32_t xb_offset = GPS_L5Q_INIT_REG[prn];
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const std::deque<bool> xb = make_l5q_xb();
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const std::deque<bool> xa = make_l5q_xa();
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std::deque<bool> xb_shift(GPS_L5Q_CODE_LENGTH_CHIPS, false);
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for (int32_t n = 0; n < GPS_L5Q_CODE_LENGTH_CHIPS; n++)
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{
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xb_shift[n] = xb[(xb_offset + n) % GPS_L5Q_CODE_LENGTH_CHIPS];
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}
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for (int32_t n = 0; n < GPS_L5Q_CODE_LENGTH_CHIPS; n++)
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{
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dest[n] = xa[n] xor xb_shift[n];
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}
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}
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void gps_l5i_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_L5I_CODE_LENGTH_CHIPS> code_aux{};
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if (prn > 0 and prn < 51)
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{
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make_l5i(code_aux, prn - 1);
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}
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for (int32_t i = 0; i < GPS_L5I_CODE_LENGTH_CHIPS; i++)
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{
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dest[i] = std::complex<float>(1.0F - 2.0F * static_cast<float>(code_aux[i]), 0.0);
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}
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}
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void gps_l5i_code_gen_float(own::span<float> dest, uint32_t prn)
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{
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std::array<int32_t, GPS_L5I_CODE_LENGTH_CHIPS> code_aux{};
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if (prn > 0 and prn < 51)
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{
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make_l5i(code_aux, prn - 1);
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}
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for (int32_t i = 0; i < GPS_L5I_CODE_LENGTH_CHIPS; i++)
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{
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dest[i] = 1.0F - 2.0F * 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 L5i code for the desired SV ID and sampled to specific sampling frequency
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*/
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void gps_l5i_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_L5I_CODE_LENGTH_CHIPS;
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constexpr float tc = 1.0 / static_cast<float>(GPS_L5I_CODE_RATE_CPS); // L5I primary chip period in sec
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const auto samplesPerCode = static_cast<int32_t>(static_cast<double>(sampling_freq) / (static_cast<double>(GPS_L5I_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_L5I_CODE_LENGTH_CHIPS> code_aux{};
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if (prn > 0 and prn < 51)
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{
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make_l5i(code_aux, prn - 1);
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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 L5 code values ---------------------
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codeValueIndex = static_cast<int32_t>(std::ceil(ts * (i + 1.0F) / tc)) - 1;
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// --- Make the digitized version of the L5I 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>(1.0F - 2.0F * code_aux[codeLength - 1], 0.0);
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}
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else
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{
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dest[i] = std::complex<float>(1.0F - 2.0F * code_aux[codeValueIndex], 0.0); // repeat the chip -> upsample
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}
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}
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}
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void gps_l5q_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_L5Q_CODE_LENGTH_CHIPS> code_aux{};
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if (prn > 0 and prn < 51)
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{
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make_l5q(code_aux, prn - 1);
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}
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for (int32_t i = 0; i < GPS_L5Q_CODE_LENGTH_CHIPS; i++)
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{
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dest[i] = std::complex<float>(0.0, 1.0F - 2.0F * static_cast<float>(code_aux[i]));
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}
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}
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void gps_l5q_code_gen_float(own::span<float> dest, uint32_t prn)
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{
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std::array<int32_t, GPS_L5Q_CODE_LENGTH_CHIPS> code_aux{};
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if (prn > 0 and prn < 51)
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{
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make_l5q(code_aux, prn - 1);
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}
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for (int32_t i = 0; i < GPS_L5Q_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 L5Q code for the desired SV ID and sampled to specific sampling frequency
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*/
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void gps_l5q_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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std::array<int32_t, GPS_L5Q_CODE_LENGTH_CHIPS> code_aux{};
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if (prn > 0 and prn < 51)
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{
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make_l5q(code_aux, prn - 1);
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}
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int32_t codeValueIndex;
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constexpr int32_t codeLength = GPS_L5Q_CODE_LENGTH_CHIPS;
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// --- Find number of samples per spreading code ---------------------------
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const auto samplesPerCode = static_cast<int32_t>(static_cast<double>(sampling_freq) / (static_cast<double>(GPS_L5Q_CODE_RATE_CPS) / static_cast<double>(codeLength)));
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// --- Find time constants -------------------------------------------------
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const float ts = 1.0F / static_cast<float>(sampling_freq); // Sampling period in sec
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constexpr float tc = 1.0F / static_cast<float>(GPS_L5Q_CODE_RATE_CPS); // L5Q 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 L5 code values ---------------------
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codeValueIndex = static_cast<int32_t>(std::ceil(ts * (i + 1.0F) / tc)) - 1;
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// --- Make the digitized version of the L5Q 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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