435 lines
14 KiB
C++
435 lines
14 KiB
C++
/***************************************************************************
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* Copyright (C) 2021 - 2022 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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#include <M17/M17Demodulator.h>
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#include <M17/M17DSP.h>
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#include <M17/M17Utils.h>
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#include <interfaces/audio_stream.h>
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#include <interfaces/gpio.h>
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#include <math.h>
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#include <cstring>
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#include <stdio.h>
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#include <interfaces/graphics.h>
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#include <deque>
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#ifdef PLATFORM_LINUX
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#include <emulator.h>
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#endif
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using namespace M17;
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M17Demodulator::M17Demodulator()
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{
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}
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M17Demodulator::~M17Demodulator()
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{
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// TODO
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// terminate();
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}
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void M17Demodulator::init()
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{
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/*
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* Allocate a chunk of memory to contain two complete buffers for baseband
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* audio. Split this chunk in two separate blocks for double buffering using
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* placement new.
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*/
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baseband_buffer = new int16_t[2 * M17_SAMPLE_BUF_SIZE];
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baseband = { nullptr, 0 };
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activeFrame = new frame_t;
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rawFrame = new uint16_t[M17_FRAME_SYMBOLS];
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idleFrame = new frame_t;
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frame_index = 0;
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phase = 0;
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syncDetected = false;
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locked = false;
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newFrame = false;
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#ifdef PLATFORM_LINUX
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FILE *csv_log = fopen("demod_log.csv", "w");
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fprintf(csv_log, "Signal,Convolution,Threshold,Offset,Sample,Max,Min,Symbol,I\n");
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fclose(csv_log);
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#endif // PLATFORM_MOD17
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}
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void M17Demodulator::terminate()
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{
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// Delete the buffers and deallocate memory.
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delete[] baseband_buffer;
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delete activeFrame;
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delete[] rawFrame;
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delete idleFrame;
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}
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void M17Demodulator::startBasebandSampling()
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{
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basebandId = inputStream_start(SOURCE_RTX, PRIO_RX,
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baseband_buffer,
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2 * M17_SAMPLE_BUF_SIZE,
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BUF_CIRC_DOUBLE,
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M17_RX_SAMPLE_RATE);
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// Clean start of the demodulation statistics
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resetCorrelationStats();
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resetQuantizationStats();
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// DC removal filter reset
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dsp_resetFilterState(&dsp_state);
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}
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void M17Demodulator::stopBasebandSampling()
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{
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inputStream_stop(basebandId);
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}
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void M17Demodulator::resetCorrelationStats()
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{
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conv_emvar = 40000000.0f;
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}
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/**
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* Algorithms taken from
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* https://fanf2.user.srcf.net/hermes/doc/antiforgery/stats.pdf
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*/
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void M17Demodulator::updateCorrelationStats(int32_t value)
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{
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float incr = CONV_STATS_ALPHA * static_cast<float>(value);
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conv_emvar = (1.0f - CONV_STATS_ALPHA) * (conv_emvar + static_cast<float>(value) * incr);
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}
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float M17Demodulator::getCorrelationStddev()
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{
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return sqrt(conv_emvar);
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}
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void M17Demodulator::resetQuantizationStats()
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{
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qnt_pos_avg = 0.0f;
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qnt_neg_avg = 0.0f;
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}
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void M17Demodulator::updateQuantizationStats(int32_t offset)
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{
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// If offset is negative use bridge buffer
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int16_t sample = 0;
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if (offset < 0) // When we are at negative offsets use bridge buffer
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sample = basebandBridge[M17_BRIDGE_SIZE + offset];
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else // Otherwise use regular data buffer
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sample = baseband.data[offset];
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if (sample > 0)
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{
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qnt_pos_fifo.push_front(sample);
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// FIFO not full, compute traditional average
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if (qnt_pos_fifo.size() <= QNT_SMA_WINDOW)
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{
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int32_t acc = 0;
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for(auto e : qnt_pos_fifo)
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acc += e;
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qnt_pos_avg = acc / static_cast<float>(qnt_pos_fifo.size());
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}
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else
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{
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qnt_pos_avg += 1 / static_cast<float>(QNT_SMA_WINDOW) *
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(sample - qnt_pos_fifo.back());
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qnt_pos_fifo.pop_back();
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}
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}
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else
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{
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qnt_neg_fifo.push_front(sample);
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// FIFO not full, compute traditional average
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if (qnt_neg_fifo.size() <= QNT_SMA_WINDOW)
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{
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int32_t acc = 0;
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for(auto e : qnt_neg_fifo)
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acc += e;
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qnt_neg_avg = acc / static_cast<float>(qnt_neg_fifo.size());
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}
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else
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{
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qnt_neg_avg += 1 / static_cast<float>(QNT_SMA_WINDOW) *
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(sample - qnt_neg_fifo.back());
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qnt_neg_fifo.pop_back();
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}
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}
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}
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int32_t M17Demodulator::convolution(int32_t offset,
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int8_t *target,
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size_t target_size)
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{
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// Compute convolution
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int32_t conv = 0;
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for(uint32_t i = 0; i < target_size; i++)
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{
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int32_t sample_index = offset + i * M17_SAMPLES_PER_SYMBOL;
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int16_t sample = 0;
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// When we are at negative indices use bridge buffer
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if (sample_index < 0)
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sample = basebandBridge[M17_BRIDGE_SIZE + sample_index];
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else
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sample = baseband.data[sample_index];
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conv += (int32_t) target[i] * (int32_t) sample;
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}
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return conv;
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}
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sync_t M17Demodulator::nextFrameSync(int32_t offset)
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{
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#ifdef PLATFORM_LINUX
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FILE *csv_log = fopen("demod_log.csv", "a");
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#endif
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sync_t syncword = { -1, false };
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// Find peaks in the correlation between the baseband and the frame syncword
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// Leverage the fact LSF syncword is the opposite of the frame syncword
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// to detect both syncwords at once. Stop early because convolution needs
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// access samples ahead of the starting offset.
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int32_t maxLen = static_cast < int32_t >(baseband.len - M17_BRIDGE_SIZE);
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for(int32_t i = offset; (syncword.index == -1) && (i < maxLen); i++)
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{
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int32_t conv = convolution(i, stream_syncword, M17_SYNCWORD_SYMBOLS);
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updateCorrelationStats(conv);
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#ifdef PLATFORM_LINUX
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int16_t sample = 0;
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if (i < 0) // When we are at negative offsets use bridge buffer
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sample = basebandBridge[M17_BRIDGE_SIZE + i];
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else // Otherwise use regular data buffer
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sample = baseband.data[i];
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fprintf(csv_log, "%" PRId16 ",%d,%f,%d,%" PRId16 ",%f,%f,%d,%d\n",
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sample,
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conv / 10,
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CONV_THRESHOLD_FACTOR * getCorrelationStddev() / 10,
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i,
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0,0.0,0.0,0,0);
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fflush(csv_log);
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#endif
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// Positive correlation peak -> frame syncword
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if (conv > (getCorrelationStddev() * CONV_THRESHOLD_FACTOR))
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{
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syncword.lsf = false;
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syncword.index = i;
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}
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// Negative correlation peak -> LSF syncword
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else if (conv < -(getCorrelationStddev() * CONV_THRESHOLD_FACTOR))
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{
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syncword.lsf = true;
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syncword.index = i;
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}
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}
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#ifdef PLATFORM_LINUX
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fclose(csv_log);
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#endif
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return syncword;
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}
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int8_t M17Demodulator::quantize(int32_t offset)
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{
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int16_t sample = 0;
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if (offset < 0) // When we are at negative offsets use bridge buffer
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sample = basebandBridge[M17_BRIDGE_SIZE + offset];
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else // Otherwise use regular data buffer
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sample = baseband.data[offset];
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if (sample > static_cast< int16_t >(qnt_pos_avg / 2.1))
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return +3;
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else if (sample < static_cast< int16_t >(qnt_neg_avg / 2.1))
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return -3;
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else if (sample > 0)
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return +1;
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else
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return -1;
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}
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const frame_t& M17Demodulator::getFrame()
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{
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// When a frame is read is not new anymore
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newFrame = false;
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return *activeFrame;
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}
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bool M17::M17Demodulator::isLocked()
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{
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return locked;
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}
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uint8_t M17Demodulator::hammingDistance(uint8_t x, uint8_t y)
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{
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return __builtin_popcount(x ^ y);
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}
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bool M17Demodulator::update()
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{
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M17::sync_t syncword = { 0, false };
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int32_t offset = syncDetected ? 0 : -(int32_t) M17_BRIDGE_SIZE;
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uint16_t decoded_syms = 0;
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// Read samples from the ADC
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baseband = inputStream_getData(basebandId);
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// Apply DC removal filter
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dsp_dcRemoval(&dsp_state, baseband.data, baseband.len);
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#ifdef PLATFORM_LINUX
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FILE *csv_log = fopen("demod_log.csv", "a");
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#endif
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if(baseband.data != NULL)
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{
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// Apply RRC on the baseband buffer
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for(size_t i = 0; i < baseband.len; i++)
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{
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float elem = static_cast< float >(baseband.data[i]);
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baseband.data[i] = static_cast< int16_t >(M17::rrc_24k(elem));
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}
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// Process the buffer
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while((syncword.index != -1) &&
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((static_cast< int32_t >(M17_SAMPLES_PER_SYMBOL * decoded_syms) +
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offset + phase) < static_cast < int32_t >(baseband.len)))
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{
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// If we are not demodulating a syncword, search for one
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if (!syncDetected)
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{
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syncword = nextFrameSync(offset);
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if (syncword.index != -1) // Valid syncword found
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{
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syncDetected = true;
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offset = syncword.index + 1;
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phase = 0;
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frame_index = 0;
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}
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}
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// While we detected a syncword, demodulate available samples
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else
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{
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// Slice the input buffer to extract a frame and quantize
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int32_t symbol_index = offset
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+ phase
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+ (M17_SAMPLES_PER_SYMBOL * decoded_syms);
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// Update quantization stats only on syncwords
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if (frame_index < M17_SYNCWORD_SYMBOLS)
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updateQuantizationStats(symbol_index);
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int8_t symbol = quantize(symbol_index);
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#ifdef PLATFORM_LINUX
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for (int i = 0; i < 2; i++)
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{
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if ((symbol_index - 2 + i) >= 0)
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fprintf(csv_log, "%" PRId16 ",%d,%f,%d,%" PRId16 ",%f,%f,%d,%d\n",
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0,0,0.0,symbol_index - 2 + i,
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baseband.data[symbol_index - 2 + i],
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qnt_pos_avg / 2.1,
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qnt_neg_avg / 2.1,
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0,
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frame_index);
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}
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fprintf(csv_log, "%" PRId16 ",%d,%f,%d,%" PRId16 ",%f,%f,%d,%d\n",
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0,0,0.0,symbol_index,
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baseband.data[symbol_index],
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qnt_pos_avg / 2.1,
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qnt_neg_avg / 2.1,
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symbol * 666,
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frame_index);
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for (int i = 0; i < 2; i++)
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{
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if ((symbol_index + i + 1) < static_cast<int32_t> (baseband.len))
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fprintf(csv_log, "%" PRId16 ",%d,%f,%d,%" PRId16 ",%f,%f,%d,%d\n",
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0,0,0.0,symbol_index + i + 1,
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baseband.data[symbol_index + i + 1],
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qnt_pos_avg / 2.1,
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qnt_neg_avg / 2.1,
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0,
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frame_index);
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}
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fflush(csv_log);
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#endif
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setSymbol<M17_FRAME_BYTES>(*activeFrame, frame_index, symbol);
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decoded_syms++;
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frame_index++;
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// If the frame buffer is full switch active and idle frame
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if (frame_index == M17_FRAME_SYMBOLS)
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{
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std::swap(activeFrame, idleFrame);
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frame_index = 0;
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newFrame = true;
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}
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if (frame_index == M17_SYNCWORD_SYMBOLS)
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{
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// If syncword is not valid, lock is lost, accept 2 bit errors
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uint8_t hammingSync = hammingDistance((*activeFrame)[0],
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stream_syncword_bytes[0])
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+ hammingDistance((*activeFrame)[1],
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stream_syncword_bytes[1]);
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uint8_t hammingLsf = hammingDistance((*activeFrame)[0],
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lsf_syncword_bytes[0])
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+ hammingDistance((*activeFrame)[1],
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lsf_syncword_bytes[1]);
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// Too many errors in the syncword, lock is lost
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if ((hammingSync > 4) && (hammingLsf > 4))
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{
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syncDetected = false;
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locked = false;
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std::swap(activeFrame, idleFrame);
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frame_index = 0;
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newFrame = true;
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}
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// Correct syncword found
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else
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locked = true;
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}
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}
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}
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// We are at the end of the buffer
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if (syncDetected)
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{
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// Compute phase of next buffer
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phase = (static_cast<int32_t> (phase) + offset + baseband.len) % M17_SAMPLES_PER_SYMBOL;
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}
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else
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{
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// Copy last N samples to bridge buffer
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memcpy(basebandBridge,
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baseband.data + (baseband.len - M17_BRIDGE_SIZE),
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sizeof(int16_t) * M17_BRIDGE_SIZE);
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}
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}
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#ifdef PLATFORM_LINUX
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fclose(csv_log);
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#endif
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return newFrame;
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}
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