175 lines
6.6 KiB
C++
175 lines
6.6 KiB
C++
/***************************************************************************
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* Copyright (C) 2021 - 2024 by Federico Amedeo Izzo IU2NUO, *
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* Niccolò Izzo IU2KIN *
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* Wojciech Kaczmarski SP5WWP *
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* Frederik Saraci IU2NRO *
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* Silvano Seva IU2KWO *
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* *
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* *
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* This program is free software; you can redistribute it and/or modify *
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* it under the terms of the GNU General Public License as published by *
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* the Free Software Foundation; either version 3 of the License, or *
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* (at your option) any later version. *
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* *
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* This program is distributed in the hope that it will be useful, *
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* but WITHOUT ANY WARRANTY; without even the implied warranty of *
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the *
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* GNU General Public License for more details. *
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* *
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* You should have received a copy of the GNU General Public License *
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* along with this program; if not, see <http://www.gnu.org/licenses/> *
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***************************************************************************/
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#ifndef M17_DEMODULATOR_H
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#define M17_DEMODULATOR_H
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#ifndef __cplusplus
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#error This header is C++ only!
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#endif
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#include <iir.hpp>
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#include <cstdint>
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#include <cstddef>
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#include <memory>
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#include <array>
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#include <dsp.h>
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#include <cmath>
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#include <audio_path.h>
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#include <audio_stream.h>
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#include <M17/M17Datatypes.hpp>
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#include <M17/M17Constants.hpp>
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#include <M17/Correlator.hpp>
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#include <M17/Synchronizer.hpp>
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namespace M17
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{
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class M17Demodulator
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{
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public:
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/**
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* Constructor.
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*/
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M17Demodulator();
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/**
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* Destructor.
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*/
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~M17Demodulator();
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/**
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* Allocate buffers for baseband signal sampling and initialise demodulator.
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*/
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void init();
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/**
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* Shutdown modulator and deallocate data buffers.
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*/
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void terminate();
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/**
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* Starts the sampling of the baseband signal in a double buffer.
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*/
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void startBasebandSampling();
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/**
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* Stops the sampling of the baseband signal in a double buffer.
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*/
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void stopBasebandSampling();
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/**
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* Returns the a frame decoded from the baseband signal.
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*
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* @return reference to the internal data structure containing the last
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* decoded frame.
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*/
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const frame_t& getFrame();
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/**
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* Demodulates data from the ADC and fills the idle frame.
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* Everytime this function is called a whole ADC buffer is consumed.
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*
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* @param invertPhase: invert the phase of the baseband signal before decoding.
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* @return true if a new frame has been fully decoded.
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*/
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bool update(const bool invertPhase = false);
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/**
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* @return true if a demodulator is locked on an M17 stream.
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*/
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bool isLocked();
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private:
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/**
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* Quantize a given sample to its corresponding symbol and append it to the
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* ongoing frame. When a frame is complete, it swaps the pointers and updates
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* newFrame variable.
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*
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* @param sample: baseband sample.
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* @return quantized symbol.
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*/
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int8_t updateFrame(const int16_t sample);
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/**
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* Reset the demodulator state.
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*/
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void reset();
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/**
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* M17 baseband signal sampled at 24kHz, half of an M17 frame is processed
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* at each update of the demodulator.
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*/
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static constexpr size_t RX_SAMPLE_RATE = 24000;
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static constexpr size_t SAMPLES_PER_SYMBOL = RX_SAMPLE_RATE / M17_SYMBOL_RATE;
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static constexpr size_t FRAME_SAMPLES = M17_FRAME_SYMBOLS * SAMPLES_PER_SYMBOL;
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static constexpr size_t SAMPLE_BUF_SIZE = FRAME_SAMPLES / 2;
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static constexpr size_t SYNCWORD_SAMPLES = SAMPLES_PER_SYMBOL * M17_SYNCWORD_SYMBOLS;
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/**
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* Internal state of the demodulator.
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*/
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enum class DemodState
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{
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INIT, ///< Initializing
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UNLOCKED, ///< Not locked
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SYNCED, ///< Synchronized, validate syncword
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LOCKED, ///< Locked
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SYNC_UPDATE ///< Updating the sampling point
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};
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/**
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* Cofficients of the sample filter
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*/
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static constexpr std::array < float, 3 > sfNum = {4.24433681e-05f, 8.48867363e-05f, 4.24433681e-05f};
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static constexpr std::array < float, 3 > sfDen = {1.0f, -1.98148851f, 0.98165828f};
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DemodState demodState; ///< Demodulator state
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std::unique_ptr< int16_t[] > baseband_buffer; ///< Buffer for baseband audio handling.
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streamId basebandId; ///< Id of the baseband input stream.
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pathId basebandPath; ///< Id of the baseband input path.
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std::unique_ptr<frame_t > demodFrame; ///< Frame being demodulated.
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std::unique_ptr<frame_t > readyFrame; ///< Fully demodulated frame to be returned.
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bool locked; ///< A syncword was correctly demodulated.
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bool newFrame; ///< A new frame has been fully decoded.
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uint16_t frameIndex; ///< Index for filling the raw frame.
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uint32_t sampleIndex; ///< Sample index, from 0 to (SAMPLES_PER_SYMBOL - 1)
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uint32_t samplingPoint; ///< Symbol sampling point
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uint32_t sampleCount; ///< Free-running sample counter
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uint8_t missedSyncs; ///< Counter of missed synchronizations
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uint32_t initCount; ///< Downcounter for initialization
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uint32_t syncCount; ///< Downcounter for resynchronization
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std::pair < int32_t, int32_t > outerDeviation; ///< Deviation of outer symbols
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float corrThreshold; ///< Correlation threshold
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filter_state_t dcrState; ///< State of the DC removal filter
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Correlator < M17_SYNCWORD_SYMBOLS, SAMPLES_PER_SYMBOL > correlator;
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Synchronizer < M17_SYNCWORD_SYMBOLS, SAMPLES_PER_SYMBOL > streamSync{{ -3, -3, -3, -3, +3, +3, -3, +3 }};
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Iir < 3 > sampleFilter{sfNum, sfDen};
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};
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} /* M17 */
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#endif /* M17_DEMODULATOR_H */
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