I want to modify the code of gqrx to automatically identify the peaks of LoRAWAN (Chir

Identify Chirp Spread Spectrum Signals about gqrx HOT 2 OPEN

alphapats commented on May 23, 2024 1

Identify Chirp Spread Spectrum Signals

from gqrx.

Comments (2)

argilo commented on May 23, 2024

If you'd like to experiment with the peak detection algorithm, you can find the code in plotter.cpp:

gqrx/src/qtgui/plotter.cpp

Lines 1638 to 1738 in 848acef

 // Peak detection 

 if (m_PeakDetectActive) 

 { 

 const int pw = PEAK_WINDOW_HALF_WIDTH; 

 // Use data source appropriate for current display mode 

 float *_detectSource; 

 if (m_MaxHoldActive) 

 _detectSource = m_fftMaxHoldBuf; 

 else if (m_PlotMode == PLOT_MODE_AVG) 

 _detectSource = m_fftAvgBuf; 

 else 

 _detectSource = m_fftMaxBuf; 

 const float *detectSource = _detectSource; 

 // Run peak detection periodically. If overlay will be redrawn, run 

 // peak detection since zoom/pan may have changed. 

 if (tnow_ms > tlast_peaks_ms + PEAK_UPDATE_PERIOD || m_DrawOverlay) { 

 tlast_peaks_ms = tnow_ms; 

 m_Peaks.clear(); 

 // Narrow peaks 

 for (i = pw; i < npts - pw; ++i) { 

 const int ix = i + xmin; 

 const float vi = detectSource[ix]; 

 float sumV = 0; 

 float minV = vi; 

 float maxV = 0; 

 for (j = -pw; j <= pw; ++j) { 

 const float vj = detectSource[ix + j]; 

 minV = std::min(minV, vj); 

 maxV = std::max(maxV, vj); 

 sumV += vj; 

 } 

 const float avgV = sumV / (float)(pw * 2 + 1); 

 m_peakSmoothBuf[ix] = avgV; 

 if (vi == maxV && (vi > 2.0f * avgV) && (vi > 4.0f * minV)) 

 { 

 const qreal y = (qreal)std::max(std::min( 

 panddBGainFactor * (m_PandMaxdB - 10.0f * log10f(vi)), 

 (float)plotHeight - 0.0f), 0.0f); 

 m_Peaks[ix] = y; 

 } 

 } 

 // Use the smoothed curve to find wider peaks 

 const int pw2 = pw * 5; 

 for (i = pw2; i < npts - pw2; ++i) { 

 const int ix = i + xmin; 

 const float vi = m_peakSmoothBuf[ix]; 

 float sumV = 0; 

 float minV = vi; 

 float maxV = 0; 

 for (j = -pw2; j <= pw2; ++j) { 

 const float vj = m_peakSmoothBuf[ix + j]; 

 minV = std::min(minV, vj); 

 maxV = std::max(maxV, vj); 

 sumV += vj; 

 } 

 const float avgV = sumV / (float)(pw2 * 2); 

 if (vi == maxV && (vi > 2.0f * avgV) && (vi > 4.0f * minV)) 

 { 

 const qreal y = (qreal)std::max(std::min( 

 panddBGainFactor * (m_PandMaxdB - 10.0f * log10f(vi)), 

 (float)plotHeight - 0.0f), 0.0f); 

 // Show the wider peak only if there is no very close narrow peak 

 bool found = false; 

 for (j = -pw; j <= pw; ++j) { 

 auto it = m_Peaks.find(ix + j); 

 if (it != m_Peaks.end()) { 

 found = true; 

 break; 

 } 

 } 

 if (!found) { 

 m_Peaks[ix] = y; 

 } 

 } 

 } 

 } 

 // Paint peaks with shadow 

 QPen peakPen(m_maxFftColor, m_DPR); 

 QPen peakShadowPen(Qt::black, m_DPR); 

 peakPen.setWidthF(m_DPR); 

 for(auto peakx : m_Peaks.keys()) { 

 const qreal peakxPlot = (qreal)peakx; 

 const qreal peakv = m_Peaks.value(peakx); 

 painter2.setPen(peakShadowPen); 

 painter2.drawEllipse( 

 QRectF(peakxPlot - 5.0 * m_DPR + shadowOffset, 

 peakv - 5.0 * m_DPR + shadowOffset, 

 10.0 * m_DPR, 10.0 * m_DPR)); 

 painter2.setPen(peakPen); 

 painter2.drawEllipse( 

 QRectF(peakxPlot - 5.0 * m_DPR, 

 peakv - 5.0 * m_DPR, 

 10.0 * m_DPR, 10.0 * m_DPR)); 

 } 

 }

from gqrx.

alphapats commented on May 23, 2024

Thanks, will try that

from gqrx.

Identify Chirp Spread Spectrum Signals about gqrx HOT 2 OPEN

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	// Peak detection
	if (m_PeakDetectActive)
	{
	const int pw = PEAK_WINDOW_HALF_WIDTH;

	// Use data source appropriate for current display mode
	float *_detectSource;
	if (m_MaxHoldActive)
	_detectSource = m_fftMaxHoldBuf;
	else if (m_PlotMode == PLOT_MODE_AVG)
	_detectSource = m_fftAvgBuf;
	else
	_detectSource = m_fftMaxBuf;
	const float *detectSource = _detectSource;

	// Run peak detection periodically. If overlay will be redrawn, run
	// peak detection since zoom/pan may have changed.
	if (tnow_ms > tlast_peaks_ms + PEAK_UPDATE_PERIOD \|\| m_DrawOverlay) {
	tlast_peaks_ms = tnow_ms;
	m_Peaks.clear();

	// Narrow peaks
	for (i = pw; i < npts - pw; ++i) {
	const int ix = i + xmin;
	const float vi = detectSource[ix];
	float sumV = 0;
	float minV = vi;
	float maxV = 0;
	for (j = -pw; j <= pw; ++j) {
	const float vj = detectSource[ix + j];
	minV = std::min(minV, vj);
	maxV = std::max(maxV, vj);
	sumV += vj;
	}
	const float avgV = sumV / (float)(pw * 2 + 1);
	m_peakSmoothBuf[ix] = avgV;
	if (vi == maxV && (vi > 2.0f * avgV) && (vi > 4.0f * minV))
	{
	const qreal y = (qreal)std::max(std::min(
	panddBGainFactor * (m_PandMaxdB - 10.0f * log10f(vi)),
	(float)plotHeight - 0.0f), 0.0f);
	m_Peaks[ix] = y;
	}
	}

	// Use the smoothed curve to find wider peaks
	const int pw2 = pw * 5;
	for (i = pw2; i < npts - pw2; ++i) {
	const int ix = i + xmin;
	const float vi = m_peakSmoothBuf[ix];
	float sumV = 0;
	float minV = vi;
	float maxV = 0;
	for (j = -pw2; j <= pw2; ++j) {
	const float vj = m_peakSmoothBuf[ix + j];
	minV = std::min(minV, vj);
	maxV = std::max(maxV, vj);
	sumV += vj;
	}
	const float avgV = sumV / (float)(pw2 * 2);
	if (vi == maxV && (vi > 2.0f * avgV) && (vi > 4.0f * minV))
	{
	const qreal y = (qreal)std::max(std::min(
	panddBGainFactor * (m_PandMaxdB - 10.0f * log10f(vi)),
	(float)plotHeight - 0.0f), 0.0f);

	// Show the wider peak only if there is no very close narrow peak
	bool found = false;
	for (j = -pw; j <= pw; ++j) {
	auto it = m_Peaks.find(ix + j);
	if (it != m_Peaks.end()) {
	found = true;
	break;
	}
	}
	if (!found) {
	m_Peaks[ix] = y;
	}
	}
	}
	}

	// Paint peaks with shadow
	QPen peakPen(m_maxFftColor, m_DPR);
	QPen peakShadowPen(Qt::black, m_DPR);
	peakPen.setWidthF(m_DPR);
	for(auto peakx : m_Peaks.keys()) {
	const qreal peakxPlot = (qreal)peakx;
	const qreal peakv = m_Peaks.value(peakx);
	painter2.setPen(peakShadowPen);
	painter2.drawEllipse(
	QRectF(peakxPlot - 5.0 * m_DPR + shadowOffset,
	peakv - 5.0 * m_DPR + shadowOffset,
	10.0 * m_DPR, 10.0 * m_DPR));
	painter2.setPen(peakPen);
	painter2.drawEllipse(
	QRectF(peakxPlot - 5.0 * m_DPR,
	peakv - 5.0 * m_DPR,
	10.0 * m_DPR, 10.0 * m_DPR));
	}
	}