sdrangel/plugins/channel/nfm/nfmdemod.cpp

///////////////////////////////////////////////////////////////////////////////////
// Copyright (C) 2012 maintech GmbH, Otto-Hahn-Str. 15, 97204 Hoechberg, Germany //
// written by Christian Daniel                                                   //
//                                                                               //
// 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                  //
//                                                                               //
// 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 <QTime>
#include <stdio.h>
#include <complex.h>
#include "nfmdemod.h"
#include "nfmdemodgui.h"
#include "audio/audiooutput.h"
#include "dsp/dspcommands.h"
#include "dsp/pidcontroller.h"

#include <iostream>

static const Real afSqTones[2] = {2000.0, 8000.0};

MESSAGE_CLASS_DEFINITION(NFMDemod::MsgConfigureNFMDemod, Message)

NFMDemod::NFMDemod(AudioFifo* audioFifo, SampleSink* sampleSink) :
	m_ctcssIndex(0),
	m_sampleCount(0),
	m_afSquelch(2, afSqTones),
	m_squelchOpen(false),
	m_sampleSink(sampleSink),
	m_audioFifo(audioFifo)
{
	m_config.m_inputSampleRate = 96000;
	m_config.m_inputFrequencyOffset = 0;
	m_config.m_rfBandwidth = 12500;
	m_config.m_afBandwidth = 3000;
	m_config.m_squelch = -30.0;
	m_config.m_volume = 2.0;
	m_config.m_audioSampleRate = 48000;

	apply();

	m_audioBuffer.resize(16384);
	m_audioBufferFill = 0;

	m_movingAverage.resize(16, 0);
	m_agcLevel = 0.003;
	m_AGC.resize(4096, m_agcLevel, 0, 0.1*m_agcLevel);

	m_ctcssDetector.setCoefficients(3000, 6000.0); // 0.5s / 2 Hz resolution
	m_afSquelch.setCoefficients(24, 48000.0, 1, 1); // 4000 Hz span, 250us
	m_afSquelch.setThreshold(0.001);
}

NFMDemod::~NFMDemod()
{
}

void NFMDemod::configure(MessageQueue* messageQueue, Real rfBandwidth, Real afBandwidth, Real volume, Real squelch)
{
	Message* cmd = MsgConfigureNFMDemod::create(rfBandwidth, afBandwidth, volume, squelch);
	cmd->submit(messageQueue, this);
}

float arctan2(Real y, Real x)
{
	Real coeff_1 = M_PI / 4;
	Real coeff_2 = 3 * coeff_1;
	Real abs_y = fabs(y) + 1e-10;      // kludge to prevent 0/0 condition
	Real angle;
	if( x>= 0) {
		Real r = (x - abs_y) / (x + abs_y);
		angle = coeff_1 - coeff_1 * r;
	} else {
		Real r = (x + abs_y) / (abs_y - x);
		angle = coeff_2 - coeff_1 * r;
	}
	if(y < 0)
		return(-angle);
	else return(angle);
}

Real angleDist(Real a, Real b)
{
	Real dist = b - a;

	while(dist <= M_PI)
		dist += 2 * M_PI;
	while(dist >= M_PI)
		dist -= 2 * M_PI;

	return dist;
}

void NFMDemod::feed(SampleVector::const_iterator begin, SampleVector::const_iterator end, bool firstOfBurst)
{
	Complex ci;

	if(m_audioFifo->size() <= 0)
		return;

	for(SampleVector::const_iterator it = begin; it != end; ++it) {
		Complex c(it->real() / 32768.0, it->imag() / 32768.0);
		c *= m_nco.nextIQ();

		{
			if(m_interpolator.interpolate(&m_interpolatorDistanceRemain, c, &ci)) {
				m_sampleBuffer.push_back(Sample(ci.real() * 32767.0, ci.imag() * 32767.0));

				qint16 sample;

				m_AGC.feed(abs(ci));
				ci *= (m_agcLevel / m_AGC.getValue());

				// demod
				/*
				Real argument = arg(ci);
				Real demod = argument - m_lastArgument;
				m_lastArgument = argument;
				*/

				/*
				// Original NFM
				Complex d = conj(m_m1Sample) * ci;
				Real demod = atan2(d.imag(), d.real());
				demod /= M_PI;
				*/

				/*
				Real argument1 = arg(ci);//atan2(ci.imag(), ci.real());
				Real argument2 = m_lastSample.real();
				Real demod = angleDist(argument2, argument1);
				m_lastSample = Complex(argument1, 0);
				*/

				// Alternative without atan - needs AGC
				// http://www.embedded.com/design/configurable-systems/4212086/DSP-Tricks--Frequency-demodulation-algorithms-
				Real ip = ci.real() - m_m2Sample.real();
				Real qp = ci.imag() - m_m2Sample.imag();
				Real h1 = m_m1Sample.real() * qp;
				Real h2 = m_m1Sample.imag() * ip;
				Real demod = (h1 - h2) * 10000;

				m_m2Sample = m_m1Sample;
				m_m1Sample = ci;
				m_sampleCount++;

				// AF processing

				if(m_afSquelch.analyze(&demod)) {
					m_squelchOpen = m_afSquelch.open();
				}

				if (m_squelchOpen)
				{
					Real ctcss_sample = m_lowpass.filter(demod);

					if ((m_sampleCount & 7) == 7) // decimate 48k -> 6k
					{
						if (m_ctcssDetector.analyze(&ctcss_sample))
						{
							int maxToneIndex;

							if (m_ctcssDetector.getDetectedTone(maxToneIndex))
							{
								if (maxToneIndex+1 != m_ctcssIndex) {
									m_nfmDemodGUI->setCtcssFreq(m_ctcssDetector.getToneSet()[maxToneIndex]);
									m_ctcssIndex = maxToneIndex+1;
								}
							}
							else
							{
								if (m_ctcssIndex != 0) {
									m_nfmDemodGUI->setCtcssFreq(0);
									m_ctcssIndex = 0;
								}
							}
						}
					}

					if (m_ctcssIndexSelected && (m_ctcssIndexSelected != m_ctcssIndex))
					{
						sample = 0;
					}
					else
					{
						demod = m_bandpass.filter(demod);
						demod *= m_running.m_volume;
						sample = demod * ((1<<15)/301); // denominator = bandpass filter number of taps
					}
				}
				else
				{
					if (m_ctcssIndex != 0) {
						m_nfmDemodGUI->setCtcssFreq(0);
						m_ctcssIndex = 0;
					}

					m_AGC.close();
					sample = 0;
				}

				m_audioBuffer[m_audioBufferFill].l = sample;
				m_audioBuffer[m_audioBufferFill].r = sample;
				++m_audioBufferFill;
				if(m_audioBufferFill >= m_audioBuffer.size()) {
					uint res = m_audioFifo->write((const quint8*)&m_audioBuffer[0], m_audioBufferFill, 1);
					if(res != m_audioBufferFill)
						qDebug("lost %u audio samples", m_audioBufferFill - res);
					m_audioBufferFill = 0;
				}

				m_interpolatorDistanceRemain += m_interpolatorDistance;
			}
		}
	}
	if(m_audioBufferFill > 0) {
		uint res = m_audioFifo->write((const quint8*)&m_audioBuffer[0], m_audioBufferFill, 1);
		if(res != m_audioBufferFill)
			qDebug("lost %u samples", m_audioBufferFill - res);
		m_audioBufferFill = 0;
	}

	if(m_sampleSink != NULL)
		m_sampleSink->feed(m_sampleBuffer.begin(), m_sampleBuffer.end(), false);
	m_sampleBuffer.clear();
}

void NFMDemod::start()
{
	m_audioFifo->clear();
	m_interpolatorRegulation = 0.9999;
	m_interpolatorDistance = 1.0;
	m_interpolatorDistanceRemain = 0.0;
	m_m1Sample = 0;
}

void NFMDemod::stop()
{
}

bool NFMDemod::handleMessage(Message* cmd)
{
	if(DSPSignalNotification::match(cmd)) {
		DSPSignalNotification* signal = (DSPSignalNotification*)cmd;

		m_config.m_inputSampleRate = signal->getSampleRate();
		m_config.m_inputFrequencyOffset = signal->getFrequencyOffset();
		apply();
		cmd->completed();
		return true;
	} else if(MsgConfigureNFMDemod::match(cmd)) {
		MsgConfigureNFMDemod* cfg = (MsgConfigureNFMDemod*)cmd;
		m_config.m_rfBandwidth = cfg->getRFBandwidth();
		m_config.m_afBandwidth = cfg->getAFBandwidth();
		m_config.m_volume = cfg->getVolume();
		m_config.m_squelch = cfg->getSquelch();
		apply();
		return true;
	} else {
		if(m_sampleSink != NULL)
		   return m_sampleSink->handleMessage(cmd);
		else return false;
	}
}

void NFMDemod::apply()
{
	if((m_config.m_inputFrequencyOffset != m_running.m_inputFrequencyOffset) ||
		(m_config.m_inputSampleRate != m_running.m_inputSampleRate)) {
		m_nco.setFreq(-m_config.m_inputFrequencyOffset, m_config.m_inputSampleRate);
	}

	if((m_config.m_inputSampleRate != m_running.m_inputSampleRate) ||
		(m_config.m_rfBandwidth != m_running.m_rfBandwidth)) {
		m_interpolator.create(16, m_config.m_inputSampleRate, m_config.m_rfBandwidth / 2.2);
		m_interpolatorDistanceRemain = 0;
		m_interpolatorDistance =  (Real) m_config.m_inputSampleRate / (Real) m_config.m_audioSampleRate;
	}

	if((m_config.m_afBandwidth != m_running.m_afBandwidth) ||
		(m_config.m_audioSampleRate != m_running.m_audioSampleRate)) {
		m_lowpass.create(301, m_config.m_audioSampleRate, 250.0);
		m_bandpass.create(301, m_config.m_audioSampleRate, 300.0, m_config.m_afBandwidth);
	}

	if(m_config.m_squelch != m_running.m_squelch) {
		m_squelchLevel = pow(10.0, m_config.m_squelch / 10.0);
		m_squelchLevel *= m_squelchLevel;
		m_afSquelch.setThreshold(m_squelchLevel);
		m_afSquelch.reset();
	}

	m_running.m_inputSampleRate = m_config.m_inputSampleRate;
	m_running.m_inputFrequencyOffset = m_config.m_inputFrequencyOffset;
	m_running.m_rfBandwidth = m_config.m_rfBandwidth;
	m_running.m_squelch = m_config.m_squelch;
	m_running.m_volume = m_config.m_volume;
	m_running.m_audioSampleRate = m_config.m_audioSampleRate;
}