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https://github.com/f4exb/sdrangel.git
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303 lines
12 KiB
C++
303 lines
12 KiB
C++
///////////////////////////////////////////////////////////////////////////////////
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// Copyright (C) 2019 Edouard Griffiths, F4EXB //
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// Copyright (C) 2020 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 <stdio.h>
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#include <complex.h>
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#include <cmath>
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#include <QTime>
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#include <QDebug>
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#include "util/stepfunctions.h"
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#include "util/db.h"
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#include "util/crc.h"
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#include "audio/audiooutput.h"
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#include "dsp/dspengine.h"
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#include "dsp/dspcommands.h"
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#include "dsp/devicesamplemimo.h"
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#include "device/deviceapi.h"
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#include "adsbdemodreport.h"
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#include "adsbdemodsink.h"
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#include "adsb.h"
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ADSBDemodSink::ADSBDemodSink() :
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m_channelSampleRate(6000000),
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m_channelFrequencyOffset(0),
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m_sampleIdx(0),
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m_sampleCount(0),
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m_skipCount(0),
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m_correlationThresholdLinear(0.0),
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m_magsq(0.0f),
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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_messageQueueToGUI(nullptr),
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m_sampleBuffer(nullptr)
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{
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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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ADSBDemodSink::~ADSBDemodSink()
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{
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delete m_sampleBuffer;
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}
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void ADSBDemodSink::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)
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{
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processOneSample(c);
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}
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else 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 ADSBDemodSink::processOneSample(Complex &ci)
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{
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Real sample;
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double magsqRaw = ci.real()*ci.real() + ci.imag()*ci.imag();
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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_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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sample = magsq;
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m_sampleBuffer[m_sampleCount] = sample;
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m_sampleCount++;
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// Do we have enough data for a frame
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if ((m_sampleCount >= m_totalSamples) && (m_skipCount == 0))
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{
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int startIdx = m_sampleCount - m_totalSamples;
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// Correlate received signal with expected preamble
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// chip+ indexes are 0, 2, 7, 9
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// we correlate only over 6 symbols so that the number of zero chips is twice the
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// number of one chips - empirically this is enough to get good correlation
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Real premableCorrelationOnes = 0.0;
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Real preambleCorrelationZeros = 0.0;
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for (int i = 0; i < m_samplesPerChip; i++)
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{
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premableCorrelationOnes += m_sampleBuffer[startIdx + 0*m_samplesPerChip + i];
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preambleCorrelationZeros += m_sampleBuffer[startIdx + 1*m_samplesPerChip + i];
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premableCorrelationOnes += m_sampleBuffer[startIdx + 2*m_samplesPerChip + i];
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preambleCorrelationZeros += m_sampleBuffer[startIdx + 3*m_samplesPerChip + i];
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preambleCorrelationZeros += m_sampleBuffer[startIdx + 4*m_samplesPerChip + i];
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preambleCorrelationZeros += m_sampleBuffer[startIdx + 5*m_samplesPerChip + i];
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preambleCorrelationZeros += m_sampleBuffer[startIdx + 6*m_samplesPerChip + i];
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premableCorrelationOnes += m_sampleBuffer[startIdx + 7*m_samplesPerChip + i];
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preambleCorrelationZeros += m_sampleBuffer[startIdx + 8*m_samplesPerChip + i];
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premableCorrelationOnes += m_sampleBuffer[startIdx + 9*m_samplesPerChip + i];
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preambleCorrelationZeros += m_sampleBuffer[startIdx + 10*m_samplesPerChip + i];
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preambleCorrelationZeros += m_sampleBuffer[startIdx + 11*m_samplesPerChip + i];
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}
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// If the correlation is exactly 0, it's probably no signal
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if ((premableCorrelationOnes > m_correlationThresholdLinear) &&
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(preambleCorrelationZeros < 2.0*m_correlationThresholdLinear) &&
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(premableCorrelationOnes != 0.0f))
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{
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// Skip over preamble
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startIdx += m_settings.m_samplesPerBit*ADS_B_PREAMBLE_BITS;
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// Demodulate waveform to bytes
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unsigned char data[ADS_B_ES_BYTES];
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int byteIdx = 0;
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int currentBit;
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unsigned char currentByte = 0;
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bool adsbOnly = true;
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int df;
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for (int bit = 0; bit < ADS_B_ES_BITS; bit++)
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{
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// PPM (Pulse position modulation) - Each bit spreads to two chips, 1->10, 0->01
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// Determine if bit is 1 or 0, by seeing which chip has largest combined energy over the sampling period
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Real oneSum = 0.0f;
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Real zeroSum = 0.0f;
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for (int i = 0; i < m_samplesPerChip; i++)
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{
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oneSum += m_sampleBuffer[startIdx+i];
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zeroSum += m_sampleBuffer[startIdx+m_samplesPerChip+i];
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}
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currentBit = oneSum > zeroSum;
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startIdx += m_settings.m_samplesPerBit;
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// Convert bit to bytes - MSB first
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currentByte |= currentBit << (7-(bit & 0x7));
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if ((bit & 0x7) == 0x7)
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{
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data[byteIdx++] = currentByte;
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currentByte = 0;
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// Don't try to demodulate any further, if this isn't an ADS-B frame
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// to help reduce processing overhead
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if (adsbOnly && (bit == 7))
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{
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df = ((data[0] >> 3) & ADS_B_DF_MASK);
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if ((df != 17) && (df != 18))
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break;
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}
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}
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}
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// Is ADS-B?
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df = ((data[0] >> 3) & ADS_B_DF_MASK);
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if ((df == 17) || (df == 18))
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{
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crcadsb crc;
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//int icao = (data[1] << 16) | (data[2] << 8) | data[3]; // ICAO aircraft address
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int parity = (data[11] << 16) | (data[12] << 8) | data[13]; // Parity / CRC
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crc.calculate(data, ADS_B_ES_BYTES-3);
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if (parity == crc.get())
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{
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// Got a valid frame
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// Don't try to re-demodulate the same frame
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m_skipCount = (ADS_B_ES_BITS+ADS_B_PREAMBLE_BITS)*ADS_B_CHIPS_PER_BIT*m_samplesPerChip;
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// Pass to GUI
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if (getMessageQueueToGUI())
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{
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ADSBDemodReport::MsgReportADSB *msg = ADSBDemodReport::MsgReportADSB::create(
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QByteArray((char*)data, sizeof(data)),
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premableCorrelationOnes,
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preambleCorrelationZeros/2.0);
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getMessageQueueToGUI()->push(msg);
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}
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// Pass to worker
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if (getMessageQueueToWorker())
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{
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ADSBDemodReport::MsgReportADSB *msg = ADSBDemodReport::MsgReportADSB::create(
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QByteArray((char*)data, sizeof(data)),
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premableCorrelationOnes,
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preambleCorrelationZeros/2.0);
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getMessageQueueToWorker()->push(msg);
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}
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}
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}
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}
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}
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if (m_skipCount > 0)
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m_skipCount--;
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if (m_sampleCount >= 2*m_totalSamples)
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{
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// Copy second half of buffer to first
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memcpy(&m_sampleBuffer[0], &m_sampleBuffer[m_totalSamples], m_totalSamples*sizeof(Real));
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m_sampleCount = m_totalSamples;
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}
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m_sampleIdx++;
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}
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void ADSBDemodSink::init(int samplesPerBit)
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{
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if (m_sampleBuffer)
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delete m_sampleBuffer;
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m_totalSamples = samplesPerBit*(ADS_B_PREAMBLE_BITS+ADS_B_ES_BITS);
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m_samplesPerChip = samplesPerBit/ADS_B_CHIPS_PER_BIT;
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m_sampleBuffer = new Real[2*m_totalSamples];
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}
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void ADSBDemodSink::applyChannelSettings(int channelSampleRate, int channelFrequencyOffset, bool force)
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{
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qDebug() << "ADSBDemodSink::applyChannelSettings:"
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<< " channelSampleRate: " << channelSampleRate
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<< " channelFrequencyOffset: " << channelFrequencyOffset;
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if ((channelFrequencyOffset != m_channelFrequencyOffset) ||
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(channelSampleRate != m_channelSampleRate) || force)
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{
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m_nco.setFreq(-channelFrequencyOffset, channelSampleRate);
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}
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if ((channelSampleRate != m_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_interpolatorDistanceRemain = 0;
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m_interpolatorDistance = (Real) channelSampleRate / (Real) (ADS_B_BITS_PER_SECOND * m_settings.m_samplesPerBit);
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}
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m_channelSampleRate = channelSampleRate;
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m_channelFrequencyOffset = channelFrequencyOffset;
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}
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void ADSBDemodSink::applySettings(const ADSBDemodSettings& settings, bool force)
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{
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qDebug() << "ADSBDemodSink::applySettings:"
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<< " m_inputFrequencyOffset: " << settings.m_inputFrequencyOffset
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<< " m_rfBandwidth: " << settings.m_rfBandwidth
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<< " m_correlationThreshold: " << settings.m_correlationThreshold
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<< " m_samplesPerBit: " << settings.m_samplesPerBit
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<< " force: " << force;
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if ((settings.m_rfBandwidth != m_settings.m_rfBandwidth)
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|| (settings.m_samplesPerBit != m_settings.m_samplesPerBit) || 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_interpolatorDistanceRemain = 0;
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m_interpolatorDistance = (Real) m_channelSampleRate / (Real) (ADS_B_BITS_PER_SECOND * settings.m_samplesPerBit);
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}
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if ((settings.m_samplesPerBit != m_settings.m_samplesPerBit) || force)
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{
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init(settings.m_samplesPerBit);
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}
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if ((settings.m_correlationThreshold != m_settings.m_correlationThreshold) || force) {
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m_correlationThresholdLinear = CalcDb::powerFromdB(m_settings.m_correlationThreshold);
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}
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m_settings = settings;
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}
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