261 lines
8.9 KiB
C++
261 lines
8.9 KiB
C++
/***************************************************************************
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* Copyright (C) 2021 - 2023 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 <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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namespace M17
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{
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typedef struct
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{
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int32_t index;
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bool lsf;
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}
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sync_t;
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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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* @return true if the last decoded frame is an LSF.
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*/
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bool isFrameLSF();
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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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* @return true if a new frame has been fully decoded.
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*/
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bool update();
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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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/**
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* Invert baseband signal phase before decoding.
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*
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* @param status: if set to true signal phase is inverted.
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*/
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void invertPhase(const bool status);
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private:
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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 M17_RX_SAMPLE_RATE = 24000;
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static constexpr size_t M17_SAMPLES_PER_SYMBOL = M17_RX_SAMPLE_RATE / M17_SYMBOL_RATE;
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static constexpr size_t M17_FRAME_SAMPLES = M17_FRAME_SYMBOLS * M17_SAMPLES_PER_SYMBOL;
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static constexpr size_t M17_SAMPLE_BUF_SIZE = M17_FRAME_SAMPLES / 2;
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static constexpr size_t M17_SYNCWORD_SAMPLES = M17_SAMPLES_PER_SYMBOL * M17_SYNCWORD_SYMBOLS;
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static constexpr int8_t SYNC_SWEEP_WIDTH = 10;
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static constexpr int8_t SYNC_SWEEP_OFFSET = ceil(SYNC_SWEEP_WIDTH / M17_SAMPLES_PER_SYMBOL);
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static constexpr int16_t M17_BRIDGE_SIZE = M17_SYNCWORD_SAMPLES + 2 * SYNC_SWEEP_WIDTH;
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static constexpr float CONV_STATS_ALPHA = 0.005f;
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static constexpr float CONV_THRESHOLD_FACTOR = 3.40;
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static constexpr int16_t QNT_SMA_WINDOW = 8;
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/**
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* M17 syncwords;
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*/
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int8_t lsf_syncword[M17_SYNCWORD_SYMBOLS] = { +3, +3, +3, +3, -3, -3, +3, -3 };
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int8_t stream_syncword[M17_SYNCWORD_SYMBOLS] = { -3, -3, -3, -3, +3, +3, -3, +3 };
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/*
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* Buffers
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*/
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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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dataBlock_t baseband; ///< Data block with samples to be processed.
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uint16_t frame_index; ///< Index for filling the raw frame.
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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 syncDetected; ///< A syncword was detected.
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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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int16_t basebandBridge[M17_BRIDGE_SIZE] = { 0 }; ///< Bridge buffer
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int16_t phase; ///< Phase of the signal w.r.t. sampling
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bool invPhase; ///< Invert signal phase
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/*
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* State variables
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*/
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bool m17RxEnabled; ///< M17 Reception Enabled
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/*
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* Convolution statistics computation
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*/
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float conv_emvar = 0.0f;
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/*
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* Quantization statistics computation
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*/
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int8_t qnt_pos_cnt; ///< Number of received positive samples
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int8_t qnt_neg_cnt; ///< Number of received negative samples
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int32_t qnt_pos_acc; ///< Accumulator for quantization average
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int32_t qnt_neg_acc; ///< Accumulator for quantization average
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float qnt_pos_avg = 0.0f; ///< Rolling average of positive samples
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float qnt_neg_avg = 0.0f; ///< Rolling average of negative samples
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/*
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* DSP filter state
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*/
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filter_state_t dsp_state;
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/**
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* Resets the exponential mean and variance/stddev computation.
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*/
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void resetCorrelationStats();
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/**
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* Updates the mean and variance with the given correlation value.
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*
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* @param value: value to be added to the exponential moving
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* average/variance computation
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*/
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void updateCorrelationStats(int32_t value);
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/**
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* Returns the standard deviation from all the correlation values.
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*
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* @returns float numerical value of the standard deviation
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*/
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float getCorrelationStddev();
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/**
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* Resets the quantization max, min and ema computation.
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*/
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void resetQuantizationStats();
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/**
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* Updates the max, min and ema for the received samples.
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*
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* @param offset: index value to be added to the exponential moving
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* average/variance computation
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*/
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void updateQuantizationStats(int32_t frame_index, int32_t symbol_index);
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/**
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* Computes the convolution between a stride of samples starting from
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* a given offset and a target waveform.
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*
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* @param offset: the offset in the active buffer where to start the stride
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* @param target: a buffer containing the target waveform to be convoluted
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* @param target_size: the number of symbols of the target waveform
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* @return uint16_t numerical value of the convolution
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*/
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int32_t convolution(int32_t offset, int8_t *target, size_t target_size);
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/**
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* Finds the index of the next frame syncword in the baseband stream.
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*
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* @param baseband: buffer containing the sampled baseband signal
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* @param offset: offset of the buffer after which syncword are searched
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* @return uint16_t index of the first syncword in the buffer after the offset
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*/
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sync_t nextFrameSync(int32_t offset);
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/**
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* Takes the value from the input baseband at a given offsets and quantizes
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* it leveraging the quantization max and min hold statistics.
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*
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* @param offset: the offset in the input baseband
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* @return int8_t quantized symbol
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*/
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int8_t quantize(int32_t offset);
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/**
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* Perform a limited search for a syncword using correlation
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*
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* @param offset: sample index right after a syncword
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* @return int32_t sample of the beginning of a syncword
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*/
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int32_t syncwordSweep(int32_t offset);
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};
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} /* M17 */
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#endif /* M17_DEMODULATOR_H */
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