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182 lines
6.5 KiB
C++
182 lines
6.5 KiB
C++
/*!
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* \file beidou_b1i_signal_processing.cc
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* \brief This class implements various functions for BeiDou B1I signal
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* \author Sergi Segura, 2018. sergi.segura.munoz(at)gmail.com
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*
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* Detailed description of the file here if needed.
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*
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* -------------------------------------------------------------------------
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*
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* Copyright (C) 2010-2019 (see AUTHORS file for a list of contributors)
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*
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* GNSS-SDR is a software defined Global Navigation
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* Satellite Systems receiver
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*
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* This file is part of GNSS-SDR.
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*
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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 "beidou_b1i_signal_processing.h"
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#include <array>
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#include <bitset>
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#include <string>
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auto auxCeil = [](float x) { return static_cast<int32_t>(static_cast<int64_t>((x) + 1)); };
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void beidou_b1i_code_gen_int(gsl::span<int32_t> _dest, int32_t _prn, uint32_t _chip_shift)
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{
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const uint32_t _code_length = 2046;
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std::bitset<_code_length> G1{};
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std::bitset<_code_length> G2{};
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std::bitset<11> G1_register(std::string("01010101010"));
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std::bitset<11> G2_register(std::string("01010101010"));
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bool feedback1;
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bool feedback2;
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bool aux;
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uint32_t lcv;
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uint32_t lcv2;
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uint32_t delay;
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int32_t prn_idx;
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const std::array<int32_t, 33> delays = {712 /*PRN1*/, 1581, 1414, 1550, 581, 771, 1311, 1043, 1549, 359, 710, 1579, 1548, 1103, 579, 769, 358, 709, 1411, 1547,
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1102, 578, 357, 1577, 1410, 1546, 1101, 707, 1576, 1409, 1545, 354 /*PRN32*/,
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705};
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const std::array<int32_t, 37> phase1 = {1, 1, 1, 1, 1, 1, 1, 1, 2, 3, 3, 3, 3, 3, 3, 3, 4, 4, 4, 4, 4, 4, 5, 5, 5, 5, 5, 6, 6, 6, 6, 8, 8, 8, 9, 9, 10};
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const std::array<int32_t, 37> phase2 = {3, 4, 5, 6, 8, 9, 10, 11, 7, 4, 5, 6, 8, 9, 10, 11, 5, 6, 8, 9, 10, 11, 6, 8, 9, 10, 11, 8, 9, 10, 11, 9, 10, 11, 10, 11, 11};
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// compute delay array index for given PRN number
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prn_idx = _prn - 1;
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// A simple error check
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if ((prn_idx < 0) || (prn_idx > 32))
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{
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return;
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}
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// Generate G1 & G2 Register
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for (lcv = 0; lcv < _code_length; lcv++)
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{
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G1[lcv] = G1_register[0];
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G2[lcv] = G2_register[-(phase1[prn_idx] - 11)] xor G2_register[-(phase2[prn_idx] - 11)];
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feedback1 = G1_register[0] xor G1_register[1] xor G1_register[2] xor G1_register[3] xor G1_register[4] xor G1_register[10];
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feedback2 = G2_register[0] xor G2_register[2] xor G2_register[3] xor G2_register[6] xor G2_register[7] xor G2_register[8] xor G2_register[9] xor G2_register[10];
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for (lcv2 = 0; lcv2 < 10; lcv2++)
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{
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G1_register[lcv2] = G1_register[lcv2 + 1];
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G2_register[lcv2] = G2_register[lcv2 + 1];
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}
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G1_register[10] = feedback1;
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G2_register[10] = feedback2;
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}
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// Set the delay
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delay = _code_length - delays[prn_idx] * 0; //**********************************
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delay += _chip_shift;
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delay %= _code_length;
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// Generate PRN from G1 and G2 Registers
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for (lcv = 0; lcv < _code_length; lcv++)
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{
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aux = G1[(lcv + _chip_shift) % _code_length] xor G2[delay];
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if (aux == true)
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{
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_dest[lcv] = 1;
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}
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else
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{
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_dest[lcv] = -1;
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}
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delay++;
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delay %= _code_length;
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}
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}
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void beidou_b1i_code_gen_float(gsl::span<float> _dest, int32_t _prn, uint32_t _chip_shift)
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{
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const uint32_t _code_length = 2046;
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std::array<int32_t, _code_length> b1i_code_int{};
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beidou_b1i_code_gen_int(gsl::span<int32_t>(b1i_code_int.data(), _code_length), _prn, _chip_shift);
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for (uint32_t ii = 0; ii < _code_length; ++ii)
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{
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_dest[ii] = static_cast<float>(b1i_code_int[ii]);
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}
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}
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void beidou_b1i_code_gen_complex(gsl::span<std::complex<float>> _dest, int32_t _prn, uint32_t _chip_shift)
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{
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const uint32_t _code_length = 2046;
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std::array<int32_t, _code_length> b1i_code_int{};
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beidou_b1i_code_gen_int(gsl::span<int32_t>(b1i_code_int.data(), _code_length), _prn, _chip_shift);
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for (uint32_t ii = 0; ii < _code_length; ++ii)
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{
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_dest[ii] = std::complex<float>(static_cast<float>(b1i_code_int[ii]), 0.0F);
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}
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}
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/*
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* Generates complex GPS L1 C/A code for the desired SV ID and sampled to specific sampling frequency
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*/
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void beidou_b1i_code_gen_complex_sampled(gsl::span<std::complex<float>> _dest, uint32_t _prn, int32_t _fs, uint32_t _chip_shift)
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{
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// This function is based on the GNU software GPS for MATLAB in the Kay Borre book
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std::array<std::complex<float>, 2046> _code{};
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int32_t _samplesPerCode;
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int32_t _codeValueIndex;
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float _ts;
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float _tc;
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float aux;
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const int32_t _codeFreqBasis = 2046000; // Hz
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const int32_t _codeLength = 2046;
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// --- Find number of samples per spreading code ---------------------------
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_samplesPerCode = static_cast<int32_t>(static_cast<double>(_fs) / (static_cast<double>(_codeFreqBasis) / static_cast<double>(_codeLength)));
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// --- Find time constants -------------------------------------------------
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_ts = 1.0 / static_cast<float>(_fs); // Sampling period in sec
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_tc = 1.0 / static_cast<float>(_codeFreqBasis); // C/A chip period in sec
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beidou_b1i_code_gen_complex(_code, _prn, _chip_shift); // generate C/A code 1 sample per chip
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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 C/A code values --------------------
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// The length of the index array depends on the sampling frequency -
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// number of samples per millisecond (because one C/A code period is one
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// millisecond).
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aux = (_ts * (i + 1)) / _tc;
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_codeValueIndex = auxCeil(aux) - 1;
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// --- Make the digitized version of the C/A code ------------------
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// The "upsampled" code is made by selecting values form the CA code
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// chip array (caCode) for the time instances of each sample.
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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] = _code[_codeLength - 1];
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}
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else
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{
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_dest[i] = _code[_codeValueIndex]; // repeat the chip -> upsample
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}
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}
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}
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