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https://github.com/f4exb/sdrangel.git
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474 lines
16 KiB
C++
474 lines
16 KiB
C++
///////////////////////////////////////////////////////////////////////////////////
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// Copyright (C) 2019 Edouard Griffiths, F4EXB //
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// Copyright (C) 2021 Jon Beniston, M7RCE //
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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 as 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 V3 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 <QDebug>
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#include <complex.h>
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#include "dsp/dspengine.h"
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#include "dsp/datafifo.h"
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#include "util/db.h"
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#include "util/stepfunctions.h"
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#include "pipes/pipeendpoint.h"
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#include "maincore.h"
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#include "aisdemod.h"
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#include "aisdemodsink.h"
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#define AISDEMOD_MINS_MAXS 5
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AISDemodSink::AISDemodSink(AISDemod *aisDemod) :
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m_scopeSink(nullptr),
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m_aisDemod(aisDemod),
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m_channelSampleRate(AISDEMOD_CHANNEL_SAMPLE_RATE),
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m_channelFrequencyOffset(0),
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m_magsqSum(0.0f),
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m_magsqPeak(0.0f),
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m_magsqCount(0),
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m_messageQueueToChannel(nullptr),
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m_rxBuf(nullptr),
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m_train(nullptr)
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{
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m_magsq = 0.0;
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m_demodBuffer.resize(1<<12);
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m_demodBufferFill = 0;
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applySettings(m_settings, true);
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applyChannelSettings(m_channelSampleRate, m_channelFrequencyOffset, true);
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}
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AISDemodSink::~AISDemodSink()
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{
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delete[] m_rxBuf;
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delete[] m_train;
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}
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void AISDemodSink::sampleToScope(Complex sample)
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{
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if (m_scopeSink)
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{
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Real r = std::real(sample) * SDR_RX_SCALEF;
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Real i = std::imag(sample) * SDR_RX_SCALEF;
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SampleVector m_sampleBuffer;
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m_sampleBuffer.push_back(Sample(r, i));
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m_scopeSink->feed(m_sampleBuffer.begin(), m_sampleBuffer.end(), true);
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m_sampleBuffer.clear();
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}
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}
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void AISDemodSink::feed(const SampleVector::const_iterator& begin, const SampleVector::const_iterator& end)
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{
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Complex ci;
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for (SampleVector::const_iterator it = begin; it != end; ++it)
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{
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Complex c(it->real(), it->imag());
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c *= m_nco.nextIQ();
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if (m_interpolatorDistance < 1.0f) // interpolate
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{
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while (!m_interpolator.interpolate(&m_interpolatorDistanceRemain, c, &ci))
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{
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processOneSample(ci);
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m_interpolatorDistanceRemain += m_interpolatorDistance;
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}
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}
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else // decimate
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{
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if (m_interpolator.decimate(&m_interpolatorDistanceRemain, c, &ci))
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{
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processOneSample(ci);
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m_interpolatorDistanceRemain += m_interpolatorDistance;
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}
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}
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}
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}
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void AISDemodSink::processOneSample(Complex &ci)
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{
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Complex ca;
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// FM demodulation
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double magsqRaw;
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Real deviation;
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Real fmDemod = m_phaseDiscri.phaseDiscriminatorDelta(ci, magsqRaw, deviation);
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// Calculate average and peak levels for level meter
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Real magsq = magsqRaw / (SDR_RX_SCALED*SDR_RX_SCALED);
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m_movingAverage(magsq);
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m_magsq = m_movingAverage.asDouble();
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m_magsqSum += magsq;
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if (magsq > m_magsqPeak)
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{
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m_magsqPeak = magsq;
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}
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m_magsqCount++;
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// Gaussian filter
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Real filt = m_pulseShape.filter(fmDemod);
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// An input frequency offset corresponds to a DC offset after FM demodulation
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// AIS spec allows up to +-1kHz offset
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// We need to remove this, otherwise it may effect the sampling
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// To calculate what it is, we sum the training sequence, which should be zero
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// Clip, as large noise can result in high correlation
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// Don't clip to 1.0 - as there may be some DC offset (1k/4.8k max dev=0.2)
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Real filtClipped;
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filtClipped = std::fmax(-1.4, std::fmin(1.4, filt));
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// Buffer filtered samples. We buffer enough samples for a max length message
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// before trying to demod, so false triggering can't make us miss anything
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m_rxBuf[m_rxBufIdx] = filtClipped;
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m_rxBufIdx = (m_rxBufIdx + 1) % m_rxBufLength;
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m_rxBufCnt = std::min(m_rxBufCnt + 1, m_rxBufLength);
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Real corr = 0.0f;
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bool scopeCRCValid = false;
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bool scopeCRCInvalid = false;
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Real dcOffset = 0.0f;
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bool thresholdMet = false;
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Real peakFreq = 0.0f;
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Real freqOffset = 0.0f;
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if (m_rxBufCnt >= m_rxBufLength)
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{
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Real trainingSum = 0.0f;
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// Correlate with training sequence
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// Note that DC offset doesn't matter for this
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// Calculate sum to estimate DC offset
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for (int i = 0; i < m_correlationLength; i++)
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{
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int j = (m_rxBufIdx + i) % m_rxBufLength;
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corr += m_train[i] * m_rxBuf[j];
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trainingSum += m_rxBuf[j];
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}
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// If we meet threshold, try to demod
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// Take abs value, to account for both initial phases
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thresholdMet = fabs(corr) >= m_settings.m_correlationThreshold;
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if (thresholdMet)
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{
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// Use mean of preamble as DC offset
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dcOffset = trainingSum/m_correlationLength;
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// Start demod after (most of) preamble
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int x = (m_rxBufIdx + m_correlationLength*3/4 + 4) % m_rxBufLength;
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// Attempt to demodulate
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bool gotSOP = false;
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int bits = 0;
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int bitCount = 0;
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int onesCount = 0;
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int byteCount = 0;
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int symbolPrev = 0;
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for (int sampleIdx = 0; sampleIdx < m_rxBufLength; sampleIdx += m_samplesPerSymbol)
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{
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// Sum and slice
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// Summing 3 samples seems to give a very small improvement vs just using 1
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int sampleCnt = 3;
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int sampleOffset = -1;
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Real sampleSum = 0.0f;
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for (int i = 0; i < sampleCnt; i++) {
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sampleSum += m_rxBuf[(x + sampleOffset + i) % m_rxBufLength] - dcOffset;
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}
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int sample = sampleSum >= 0.0f ? 1 : 0;
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// Move to next sample
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x = (x + m_samplesPerSymbol) % m_rxBufLength;
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// HDLC deframing
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// NRZI decoding
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int bit;
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if (sample != symbolPrev) {
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bit = 0;
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} else {
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bit = 1;
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}
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symbolPrev = sample;
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// Store in shift reg
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bits |= bit << bitCount;
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bitCount++;
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if (bit == 1)
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{
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onesCount++;
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// Shouldn't ever get 7 1s in a row
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if ((onesCount == 7) && gotSOP)
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{
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gotSOP = false;
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byteCount = 0;
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break;
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}
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}
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else if (bit == 0)
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{
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if (onesCount == 5)
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{
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// Remove bit-stuffing (5 1s followed by a 0)
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bitCount--;
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}
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else if (onesCount == 6)
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{
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// Start/end of packet
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if (gotSOP && (bitCount == 8) && (bits == 0x7e) && (byteCount > 0))
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{
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// End of packet
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// Check CRC is valid
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m_crc.init();
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m_crc.calculate(m_bytes, byteCount - 2);
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uint16_t calcCrc = m_crc.get();
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uint16_t rxCrc = m_bytes[byteCount-2] | (m_bytes[byteCount-1] << 8);
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if (calcCrc == rxCrc)
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{
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scopeCRCValid = true;
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QByteArray rxPacket((char *)m_bytes, byteCount - 2); // Don't include CRC
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//qDebug() << "RX: " << rxPacket.toHex();
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if (getMessageQueueToChannel())
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{
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AISDemod::MsgMessage *msg = AISDemod::MsgMessage::create(rxPacket);
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getMessageQueueToChannel()->push(msg);
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}
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// Skip over received packet, so we don't try to re-demodulate it
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m_rxBufCnt -= sampleIdx;
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}
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else
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{
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//qDebug() << QString("CRC mismatch: %1 %2").arg(calcCrc, 4, 16, QLatin1Char('0')).arg(rxCrc, 4, 16, QLatin1Char('0'));
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scopeCRCInvalid = true;
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}
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break;
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}
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else if (gotSOP)
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{
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// Repeated start flag without data or misalignment, something not right
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break;
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}
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else
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{
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// Start of packet
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gotSOP = true;
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bits = 0;
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bitCount = 0;
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byteCount = 0;
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}
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}
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onesCount = 0;
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}
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if (gotSOP)
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{
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if (bitCount == 8)
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{
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// Could also check count according to message ID as that varies
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if (byteCount >= AISDEMOD_MAX_BYTES)
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{
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// Too many bytes
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break;
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}
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else
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{
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// Got a complete byte
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m_bytes[byteCount] = bits;
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byteCount++;
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}
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bits = 0;
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bitCount = 0;
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}
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}
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// Abort demod if we haven't found start flag within a couple of bytes of presumed preamble
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if (!gotSOP && (sampleIdx >= 16 * m_samplesPerSymbol)) {
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break;
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}
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}
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}
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}
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// Select signals to feed to scope
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Complex scopeSample;
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switch (m_settings.m_scopeCh1)
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{
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case 0:
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scopeSample.real(ci.real() / SDR_RX_SCALEF);
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break;
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case 1:
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scopeSample.real(ci.imag() / SDR_RX_SCALEF);
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break;
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case 2:
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scopeSample.real(magsq);
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break;
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case 3:
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scopeSample.real(fmDemod);
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break;
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case 4:
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scopeSample.real(filt);
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break;
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case 5:
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scopeSample.real(m_rxBuf[m_rxBufIdx]);
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break;
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case 6:
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scopeSample.real(corr / 100.0);
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break;
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case 7:
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scopeSample.real(thresholdMet);
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break;
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case 8:
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scopeSample.real(dcOffset);
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break;
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case 9:
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scopeSample.real(scopeCRCValid ? 1.0 : (scopeCRCInvalid ? -1.0 : 0));
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break;
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}
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switch (m_settings.m_scopeCh2)
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{
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case 0:
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scopeSample.imag(ci.real() / SDR_RX_SCALEF);
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break;
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case 1:
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scopeSample.imag(ci.imag() / SDR_RX_SCALEF);
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break;
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case 2:
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scopeSample.imag(magsq);
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break;
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case 3:
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scopeSample.imag(fmDemod);
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break;
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case 4:
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scopeSample.imag(filt);
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break;
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case 5:
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scopeSample.imag(m_rxBuf[m_rxBufIdx]);
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break;
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case 6:
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scopeSample.imag(corr / 100.0);
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break;
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case 7:
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scopeSample.imag(thresholdMet);
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break;
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case 8:
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scopeSample.imag(dcOffset);
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break;
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case 9:
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scopeSample.imag(scopeCRCValid ? 1.0 : (scopeCRCInvalid ? -1.0 : 0));
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break;
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}
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sampleToScope(scopeSample);
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// Send demod signal to Demod Analzyer feature
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m_demodBuffer[m_demodBufferFill++] = fmDemod * std::numeric_limits<int16_t>::max();
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if (m_demodBufferFill >= m_demodBuffer.size())
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{
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QList<DataFifo*> *dataFifos = MainCore::instance()->getDataPipes().getFifos(m_channel, "demod");
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if (dataFifos)
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{
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QList<DataFifo*>::iterator it = dataFifos->begin();
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for (; it != dataFifos->end(); ++it) {
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(*it)->write((quint8*) &m_demodBuffer[0], m_demodBuffer.size() * sizeof(qint16));
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}
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}
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m_demodBufferFill = 0;
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}
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}
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void AISDemodSink::applyChannelSettings(int channelSampleRate, int channelFrequencyOffset, bool force)
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{
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qDebug() << "AISDemodSink::applyChannelSettings:"
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<< " channelSampleRate: " << channelSampleRate
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<< " channelFrequencyOffset: " << channelFrequencyOffset;
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if ((m_channelFrequencyOffset != channelFrequencyOffset) ||
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(m_channelSampleRate != channelSampleRate) || force)
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{
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m_nco.setFreq(-channelFrequencyOffset, channelSampleRate);
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}
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if ((m_channelSampleRate != channelSampleRate) || force)
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{
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m_interpolator.create(16, channelSampleRate, m_settings.m_rfBandwidth / 2.2);
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m_interpolatorDistance = (Real) channelSampleRate / (Real) AISDEMOD_CHANNEL_SAMPLE_RATE;
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m_interpolatorDistanceRemain = m_interpolatorDistance;
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}
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m_channelSampleRate = channelSampleRate;
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m_channelFrequencyOffset = channelFrequencyOffset;
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m_samplesPerSymbol = AISDEMOD_CHANNEL_SAMPLE_RATE / m_settings.m_baud;
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qDebug() << "AISDemodSink::applyChannelSettings: m_samplesPerSymbol: " << m_samplesPerSymbol;
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}
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void AISDemodSink::applySettings(const AISDemodSettings& settings, bool force)
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{
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qDebug() << "AISDemodSink::applySettings:"
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<< " force: " << force;
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if ((settings.m_rfBandwidth != m_settings.m_rfBandwidth) || force)
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{
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m_interpolator.create(16, m_channelSampleRate, settings.m_rfBandwidth / 2.2);
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m_interpolatorDistance = (Real) m_channelSampleRate / (Real) AISDEMOD_CHANNEL_SAMPLE_RATE;
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m_interpolatorDistanceRemain = m_interpolatorDistance;
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m_lowpass.create(301, AISDEMOD_CHANNEL_SAMPLE_RATE, settings.m_rfBandwidth / 2.0f);
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}
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if ((settings.m_fmDeviation != m_settings.m_fmDeviation) || force)
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{
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m_phaseDiscri.setFMScaling(AISDEMOD_CHANNEL_SAMPLE_RATE / (2.0f * settings.m_fmDeviation));
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}
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if ((settings.m_baud != m_settings.m_baud) || force)
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{
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m_samplesPerSymbol = AISDEMOD_CHANNEL_SAMPLE_RATE / settings.m_baud;
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qDebug() << "ISDemodSink::applySettings: m_samplesPerSymbol: " << m_samplesPerSymbol << " baud " << settings.m_baud;
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m_pulseShape.create(0.5, 3, m_samplesPerSymbol);
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// Recieve buffer, long enough for one max length message
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delete[] m_rxBuf;
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m_rxBufLength = AISDEMOD_MAX_BYTES*8*m_samplesPerSymbol;
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m_rxBuf = new Real[m_rxBufLength];
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m_rxBufIdx = 0;
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m_rxBufCnt = 0;
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// Create 24-bit training sequence for correlation
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delete[] m_train;
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m_correlationLength = 24*m_samplesPerSymbol;
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m_train = new Real[m_correlationLength]();
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const int trainNRZ[24] = {1, 0, 0, 1, 1, 0, 0, 1, 1, 0, 0, 1, 1, 0, 0, 1, 1, 0, 0, 1, 1, 0, 0, 1};
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// Pulse shape filter takes a few symbols before outputting expected shape
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for (int j = 0; j < m_samplesPerSymbol; j++)
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m_pulseShape.filter(-1.0f);
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for (int j = 0; j < m_samplesPerSymbol; j++)
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m_pulseShape.filter(1.0f);
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for (int i = 0; i < 24; i++)
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{
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for (int j = 0; j < m_samplesPerSymbol; j++)
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{
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m_train[i*m_samplesPerSymbol+j] = m_pulseShape.filter(trainNRZ[i] * 2.0f - 1.0f);
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}
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}
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}
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m_settings = settings;
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}
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