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sdrangel/plugins/channelrx/demodais/aisdemodsink.cpp

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///////////////////////////////////////////////////////////////////////////////////
// Copyright (C) 2019 Edouard Griffiths, F4EXB //
// Copyright (C) 2021 Jon Beniston, M7RCE //
// //
// This program is free software; you can redistribute it and/or modify //
// it under the terms of the GNU General Public License as published by //
// the Free Software Foundation as version 3 of the License, or //
// (at your option) any later version. //
// //
// This program is distributed in the hope that it will be useful, //
// but WITHOUT ANY WARRANTY; without even the implied warranty of //
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the //
// GNU General Public License V3 for more details. //
// //
// You should have received a copy of the GNU General Public License //
// along with this program. If not, see <http://www.gnu.org/licenses/>. //
///////////////////////////////////////////////////////////////////////////////////
#include <QDebug>
#include <complex.h>
#include "dsp/dspengine.h"
#include "dsp/datafifo.h"
#include "dsp/scopevis.h"
#include "util/db.h"
#include "util/stepfunctions.h"
#include "pipes/pipeendpoint.h"
#include "maincore.h"
#include "aisdemod.h"
#include "aisdemodsink.h"
AISDemodSink::AISDemodSink(AISDemod *aisDemod) :
m_scopeSink(nullptr),
m_aisDemod(aisDemod),
m_channelSampleRate(AISDemodSettings::AISDEMOD_CHANNEL_SAMPLE_RATE),
m_channelFrequencyOffset(0),
m_magsqSum(0.0f),
m_magsqPeak(0.0f),
m_magsqCount(0),
m_messageQueueToChannel(nullptr),
m_rxBuf(nullptr),
m_train(nullptr),
m_sampleBufferIndex(0)
{
m_magsq = 0.0;
m_demodBuffer.resize(1<<12);
m_demodBufferFill = 0;
m_sampleBuffer.resize(m_sampleBufferSize);
applySettings(m_settings, true);
applyChannelSettings(m_channelSampleRate, m_channelFrequencyOffset, true);
}
AISDemodSink::~AISDemodSink()
{
delete[] m_rxBuf;
delete[] m_train;
}
void AISDemodSink::sampleToScope(Complex sample)
{
if (m_scopeSink)
{
Real r = std::real(sample) * SDR_RX_SCALEF;
Real i = std::imag(sample) * SDR_RX_SCALEF;
m_sampleBuffer[m_sampleBufferIndex++] = Sample(r, i);
if (m_sampleBufferIndex == m_sampleBufferSize)
{
std::vector<SampleVector::const_iterator> vbegin;
vbegin.push_back(m_sampleBuffer.begin());
m_scopeSink->feed(vbegin, m_sampleBufferSize);
m_sampleBufferIndex = 0;
}
}
}
void AISDemodSink::feed(const SampleVector::const_iterator& begin, const SampleVector::const_iterator& end)
{
Complex ci;
for (SampleVector::const_iterator it = begin; it != end; ++it)
{
Complex c(it->real(), it->imag());
c *= m_nco.nextIQ();
if (m_interpolatorDistance < 1.0f) // interpolate
{
while (!m_interpolator.interpolate(&m_interpolatorDistanceRemain, c, &ci))
{
processOneSample(ci);
m_interpolatorDistanceRemain += m_interpolatorDistance;
}
}
else // decimate
{
if (m_interpolator.decimate(&m_interpolatorDistanceRemain, c, &ci))
{
processOneSample(ci);
m_interpolatorDistanceRemain += m_interpolatorDistance;
}
}
}
}
void AISDemodSink::processOneSample(Complex &ci)
{
Complex ca;
// FM demodulation
double magsqRaw;
Real deviation;
Real fmDemod = m_phaseDiscri.phaseDiscriminatorDelta(ci, magsqRaw, deviation);
// Calculate average and peak levels for level meter
Real magsq = magsqRaw / (SDR_RX_SCALED*SDR_RX_SCALED);
m_movingAverage(magsq);
m_magsq = m_movingAverage.asDouble();
m_magsqSum += magsq;
if (magsq > m_magsqPeak)
{
m_magsqPeak = magsq;
}
m_magsqCount++;
// Gaussian filter
Real filt = m_pulseShape.filter(fmDemod);
// An input frequency offset corresponds to a DC offset after FM demodulation
// AIS spec allows up to +-1kHz offset
// We need to remove this, otherwise it may effect the sampling
// To calculate what it is, we sum the training sequence, which should be zero
// Clip, as large noise can result in high correlation
// Don't clip to 1.0 - as there may be some DC offset (1k/4.8k max dev=0.2)
Real filtClipped;
filtClipped = std::fmax(-1.4, std::fmin(1.4, filt));
// Buffer filtered samples. We buffer enough samples for a max length message
// before trying to demod, so false triggering can't make us miss anything
m_rxBuf[m_rxBufIdx] = filtClipped;
m_rxBufIdx = (m_rxBufIdx + 1) % m_rxBufLength;
m_rxBufCnt = std::min(m_rxBufCnt + 1, m_rxBufLength);
Real corr = 0.0f;
bool scopeCRCValid = false;
bool scopeCRCInvalid = false;
Real dcOffset = 0.0f;
bool thresholdMet = false;
if (m_rxBufCnt >= m_rxBufLength)
{
Real trainingSum = 0.0f;
// Correlate with training sequence
// Note that DC offset doesn't matter for this
// Calculate sum to estimate DC offset
for (int i = 0; i < m_correlationLength; i++)
{
int j = (m_rxBufIdx + i) % m_rxBufLength;
corr += m_train[i] * m_rxBuf[j];
trainingSum += m_rxBuf[j];
}
// If we meet threshold, try to demod
// Take abs value, to account for both initial phases
thresholdMet = fabs(corr) >= m_settings.m_correlationThreshold;
if (thresholdMet)
{
// Use mean of preamble as DC offset
dcOffset = trainingSum/m_correlationLength;
// Start demod after (most of) preamble
int x = (m_rxBufIdx + m_correlationLength*3/4 + 4) % m_rxBufLength;
// Attempt to demodulate
bool gotSOP = false;
int bits = 0;
int bitCount = 0;
int onesCount = 0;
int byteCount = 0;
int symbolPrev = 0;
for (int sampleIdx = 0; sampleIdx < m_rxBufLength; sampleIdx += m_samplesPerSymbol)
{
// Sum and slice
// Summing 3 samples seems to give a very small improvement vs just using 1
int sampleCnt = 3;
int sampleOffset = -1;
Real sampleSum = 0.0f;
for (int i = 0; i < sampleCnt; i++) {
sampleSum += m_rxBuf[(x + sampleOffset + i) % m_rxBufLength] - dcOffset;
}
int symbol = sampleSum >= 0.0f ? 1 : 0;
// Move to next symbol
x = (x + m_samplesPerSymbol) % m_rxBufLength;
// HDLC deframing
// NRZI decoding
int bit;
if (symbol != symbolPrev) {
bit = 0;
} else {
bit = 1;
}
symbolPrev = symbol;
// Store in shift reg
bits |= bit << bitCount;
bitCount++;
if (bit == 1)
{
onesCount++;
// Shouldn't ever get 7 1s in a row
if ((onesCount == 7) && gotSOP)
{
gotSOP = false;
byteCount = 0;
break;
}
}
else if (bit == 0)
{
if (onesCount == 5)
{
// Remove bit-stuffing (5 1s followed by a 0)
bitCount--;
}
else if (onesCount == 6)
{
// Start/end of packet
if (gotSOP && (bitCount == 8) && (bits == 0x7e) && (byteCount > 0))
{
// End of packet
// Check CRC is valid
m_crc.init();
m_crc.calculate(m_bytes, byteCount - 2);
uint16_t calcCrc = m_crc.get();
uint16_t rxCrc = m_bytes[byteCount-2] | (m_bytes[byteCount-1] << 8);
if (calcCrc == rxCrc)
{
scopeCRCValid = true;
QByteArray rxPacket((char *)m_bytes, byteCount - 2); // Don't include CRC
//qDebug() << "RX: " << rxPacket.toHex();
if (getMessageQueueToChannel())
{
AISDemod::MsgMessage *msg = AISDemod::MsgMessage::create(rxPacket);
getMessageQueueToChannel()->push(msg);
}
// Skip over received packet, so we don't try to re-demodulate it
m_rxBufCnt -= sampleIdx;
}
else
{
//qDebug() << QString("CRC mismatch: %1 %2").arg(calcCrc, 4, 16, QLatin1Char('0')).arg(rxCrc, 4, 16, QLatin1Char('0'));
scopeCRCInvalid = true;
}
break;
}
else if (gotSOP)
{
// Repeated start flag without data or misalignment, something not right
break;
}
else
{
// Start of packet
gotSOP = true;
bits = 0;
bitCount = 0;
byteCount = 0;
}
}
onesCount = 0;
}
if (gotSOP)
{
if (bitCount == 8)
{
// Could also check count according to message ID as that varies
if (byteCount >= AISDEMOD_MAX_BYTES)
{
// Too many bytes
break;
}
else
{
// Got a complete byte
m_bytes[byteCount] = bits;
byteCount++;
}
bits = 0;
bitCount = 0;
}
}
// Abort demod if we haven't found start flag within a couple of bytes of presumed preamble
if (!gotSOP && (sampleIdx >= 16 * m_samplesPerSymbol)) {
break;
}
}
}
}
// Select signals to feed to scope
Complex scopeSample;
switch (m_settings.m_scopeCh1)
{
case 0:
scopeSample.real(ci.real() / SDR_RX_SCALEF);
break;
case 1:
scopeSample.real(ci.imag() / SDR_RX_SCALEF);
break;
case 2:
scopeSample.real(magsq);
break;
case 3:
scopeSample.real(fmDemod);
break;
case 4:
scopeSample.real(filt);
break;
case 5:
scopeSample.real(m_rxBuf[m_rxBufIdx]);
break;
case 6:
scopeSample.real(corr / 100.0);
break;
case 7:
scopeSample.real(thresholdMet);
break;
case 8:
scopeSample.real(dcOffset);
break;
case 9:
scopeSample.real(scopeCRCValid ? 1.0 : (scopeCRCInvalid ? -1.0 : 0));
break;
}
switch (m_settings.m_scopeCh2)
{
case 0:
scopeSample.imag(ci.real() / SDR_RX_SCALEF);
break;
case 1:
scopeSample.imag(ci.imag() / SDR_RX_SCALEF);
break;
case 2:
scopeSample.imag(magsq);
break;
case 3:
scopeSample.imag(fmDemod);
break;
case 4:
scopeSample.imag(filt);
break;
case 5:
scopeSample.imag(m_rxBuf[m_rxBufIdx]);
break;
case 6:
scopeSample.imag(corr / 100.0);
break;
case 7:
scopeSample.imag(thresholdMet);
break;
case 8:
scopeSample.imag(dcOffset);
break;
case 9:
scopeSample.imag(scopeCRCValid ? 1.0 : (scopeCRCInvalid ? -1.0 : 0));
break;
}
sampleToScope(scopeSample);
// Send demod signal to Demod Analzyer feature
m_demodBuffer[m_demodBufferFill++] = fmDemod * std::numeric_limits<int16_t>::max();
if (m_demodBufferFill >= m_demodBuffer.size())
{
QList<DataFifo*> *dataFifos = MainCore::instance()->getDataPipes().getFifos(m_channel, "demod");
if (dataFifos)
{
QList<DataFifo*>::iterator it = dataFifos->begin();
for (; it != dataFifos->end(); ++it) {
(*it)->write((quint8*) &m_demodBuffer[0], m_demodBuffer.size() * sizeof(qint16), DataFifo::DataTypeI16);
}
}
m_demodBufferFill = 0;
}
}
void AISDemodSink::applyChannelSettings(int channelSampleRate, int channelFrequencyOffset, bool force)
{
qDebug() << "AISDemodSink::applyChannelSettings:"
<< " channelSampleRate: " << channelSampleRate
<< " channelFrequencyOffset: " << channelFrequencyOffset;
if ((m_channelFrequencyOffset != channelFrequencyOffset) ||
(m_channelSampleRate != channelSampleRate) || force)
{
m_nco.setFreq(-channelFrequencyOffset, channelSampleRate);
}
if ((m_channelSampleRate != channelSampleRate) || force)
{
m_interpolator.create(16, channelSampleRate, m_settings.m_rfBandwidth / 2.2);
m_interpolatorDistance = (Real) channelSampleRate / (Real) AISDemodSettings::AISDEMOD_CHANNEL_SAMPLE_RATE;
m_interpolatorDistanceRemain = m_interpolatorDistance;
}
m_channelSampleRate = channelSampleRate;
m_channelFrequencyOffset = channelFrequencyOffset;
m_samplesPerSymbol = AISDemodSettings::AISDEMOD_CHANNEL_SAMPLE_RATE / m_settings.m_baud;
qDebug() << "AISDemodSink::applyChannelSettings: m_samplesPerSymbol: " << m_samplesPerSymbol;
}
void AISDemodSink::applySettings(const AISDemodSettings& settings, bool force)
{
qDebug() << "AISDemodSink::applySettings:"
<< " force: " << force;
if ((settings.m_rfBandwidth != m_settings.m_rfBandwidth) || force)
{
m_interpolator.create(16, m_channelSampleRate, settings.m_rfBandwidth / 2.2);
m_interpolatorDistance = (Real) m_channelSampleRate / (Real) AISDemodSettings::AISDEMOD_CHANNEL_SAMPLE_RATE;
m_interpolatorDistanceRemain = m_interpolatorDistance;
m_lowpass.create(301, AISDemodSettings::AISDEMOD_CHANNEL_SAMPLE_RATE, settings.m_rfBandwidth / 2.0f);
}
if ((settings.m_fmDeviation != m_settings.m_fmDeviation) || force)
{
m_phaseDiscri.setFMScaling(AISDemodSettings::AISDEMOD_CHANNEL_SAMPLE_RATE / (2.0f * settings.m_fmDeviation));
}
if ((settings.m_baud != m_settings.m_baud) || force)
{
m_samplesPerSymbol = AISDemodSettings::AISDEMOD_CHANNEL_SAMPLE_RATE / settings.m_baud;
qDebug() << "ISDemodSink::applySettings: m_samplesPerSymbol: " << m_samplesPerSymbol << " baud " << settings.m_baud;
m_pulseShape.create(0.5, 3, m_samplesPerSymbol);
// Recieve buffer, long enough for one max length message
delete[] m_rxBuf;
m_rxBufLength = AISDEMOD_MAX_BYTES*8*m_samplesPerSymbol;
m_rxBuf = new Real[m_rxBufLength];
m_rxBufIdx = 0;
m_rxBufCnt = 0;
// Create 24-bit training sequence for correlation
delete[] m_train;
m_correlationLength = 24*m_samplesPerSymbol;
m_train = new Real[m_correlationLength]();
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};
// Pulse shape filter takes a few symbols before outputting expected shape
for (int j = 0; j < m_samplesPerSymbol; j++)
m_pulseShape.filter(-1.0f);
for (int j = 0; j < m_samplesPerSymbol; j++)
m_pulseShape.filter(1.0f);
for (int i = 0; i < 24; i++)
{
for (int j = 0; j < m_samplesPerSymbol; j++)
{
m_train[i*m_samplesPerSymbol+j] = m_pulseShape.filter(trainNRZ[i] * 2.0f - 1.0f);
}
}
}
m_settings = settings;
}
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