sdrangel/plugins/channel/bfm/bfmdemod.h

///////////////////////////////////////////////////////////////////////////////////
// Copyright (C) 2015 F4EXB                                                      //
// written by Edouard Griffiths                                                  //
//                                                                               //
// 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/>.          //
///////////////////////////////////////////////////////////////////////////////////

#ifndef INCLUDE_BFMDEMOD_H
#define INCLUDE_BFMDEMOD_H

#include <QMutex>
#include <vector>
#include "dsp/samplesink.h"
#include "dsp/nco.h"
#include "dsp/interpolator.h"
#include "dsp/lowpass.h"
#include "dsp/movingaverage.h"
#include "dsp/fftfilt.h"
#include "dsp/phaselock.h"
#include "dsp/filterrc.h"
#include "audio/audiofifo.h"
#include "util/message.h"
#include "rdsdemod.h"

#define rfFilterFftLength 1024

class BFMDemod : public SampleSink {
public:
	BFMDemod(SampleSink* sampleSink);
	virtual ~BFMDemod();

	void configure(MessageQueue* messageQueue,
			Real rfBandwidth,
			Real afBandwidth,
			Real volume,
			Real squelch,
			bool audioStereo,
			bool showPilot,
			bool rdsActive);

	int getSampleRate() const { return m_config.m_inputSampleRate; }
	virtual void feed(const SampleVector::const_iterator& begin, const SampleVector::const_iterator& end, bool po);
	virtual void start();
	virtual void stop();
	virtual bool handleMessage(const Message& cmd);

	Real getMagSq() const { return m_movingAverage.average(); }
	bool getPilotLock() const { return m_pilotPLL.locked(); }
	Real getPilotLevel() const { return m_pilotPLL.get_pilot_level(); }

private:
	class MsgConfigureBFMDemod : public Message {
		MESSAGE_CLASS_DECLARATION

	public:
		Real getRFBandwidth() const { return m_rfBandwidth; }
		Real getAFBandwidth() const { return m_afBandwidth; }
		Real getVolume() const { return m_volume; }
		Real getSquelch() const { return m_squelch; }
		bool getAudioStereo() const { return m_audioStereo; }
		bool getShowPilot() const { return m_showPilot; }
		bool getRDSActive() const { return m_rdsActive; }

		static MsgConfigureBFMDemod* create(Real rfBandwidth,
				Real afBandwidth,
				Real volume,
				Real squelch,
				bool audioStereo,
				bool showPilot,
				bool rdsActive)
		{
			return new MsgConfigureBFMDemod(rfBandwidth,
					afBandwidth,
					volume,
					squelch,
					audioStereo,
					showPilot,
					rdsActive);
		}

	private:
		Real m_rfBandwidth;
		Real m_afBandwidth;
		Real m_volume;
		Real m_squelch;
		bool m_audioStereo;
		bool m_showPilot;
		bool m_rdsActive;

		MsgConfigureBFMDemod(Real rfBandwidth,
				Real afBandwidth,
				Real volume,
				Real squelch,
				bool audioStereo,
				bool showPilot,
				bool rdsActive) :
			Message(),
			m_rfBandwidth(rfBandwidth),
			m_afBandwidth(afBandwidth),
			m_volume(volume),
			m_squelch(squelch),
			m_audioStereo(audioStereo),
			m_showPilot(showPilot),
			m_rdsActive(rdsActive)
		{ }
	};

	struct AudioSample {
		qint16 l;
		qint16 r;
	};
	typedef std::vector<AudioSample> AudioVector;

	enum RateState {
		RSInitialFill,
		RSRunning
	};

	struct Config {
		int m_inputSampleRate;
		qint64 m_inputFrequencyOffset;
		Real m_rfBandwidth;
		Real m_afBandwidth;
		Real m_squelch;
		Real m_volume;
		quint32 m_audioSampleRate;
		bool m_audioStereo;
		bool m_showPilot;
		bool m_rdsActive;

		Config() :
			m_inputSampleRate(-1),
			m_inputFrequencyOffset(0),
			m_rfBandwidth(-1),
			m_afBandwidth(-1),
			m_squelch(0),
			m_volume(0),
			m_audioSampleRate(0),
			m_audioStereo(false),
			m_showPilot(false),
			m_rdsActive(false)
		{ }
	};

	Config m_config;
	Config m_running;

	NCO m_nco;
	Interpolator m_interpolator; //!< Interpolator between fixed demod bandwidth and audio bandwidth (rational)
	Real m_interpolatorDistance;
	Real m_interpolatorDistanceRemain;

	Interpolator m_interpolatorStereo; //!< Twin Interpolator for stereo subcarrier
	Real m_interpolatorStereoDistance;
	Real m_interpolatorStereoDistanceRemain;

	Interpolator m_interpolatorRDS; //!< Twin Interpolator for stereo subcarrier
	Real m_interpolatorRDSDistance;
	Real m_interpolatorRDSDistanceRemain;

	Lowpass<Real> m_lowpass;
	fftfilt* m_rfFilter;

	Real m_squelchLevel;
	int m_squelchState;

	Complex m_m1Sample; //!< x^-1 complex sample
	Complex m_m2Sample; //!< x^-2 complex sample
	Real m_m1Arg; //!> x^-1 real sample

	MovingAverage<Real> m_movingAverage;

	AudioVector m_audioBuffer;
	uint m_audioBufferFill;

	SampleSink* m_sampleSink;
	AudioFifo m_audioFifo;
	SampleVector m_sampleBuffer;
	QMutex m_settingsMutex;

	RDSPhaseLock m_pilotPLL;
	Real m_pilotPLLSamples[3];

	RDSDemod m_rdsDemod;

	LowPassFilterRC m_deemphasisFilterX;
	LowPassFilterRC m_deemphasisFilterY;
	static const Real default_deemphasis = 50.0; // 50 us

	Real m_fmExcursion;
	Real m_fmScaling;
	static const int default_excursion = 750000; // +/- 75 kHz

	/**
	 * Standard discriminator using atan2. On modern processors this is as efficient as the non atan2 one.
	 * This is better for high fidelity.
	 */
	Real phaseDiscriminator(const Complex& sample)
	{
		Complex d(std::conj(m_m1Sample) * sample);
		m_m1Sample = sample;
		return (std::atan2(d.imag(), d.real()) / M_PI_2) * m_fmScaling;
	}

	/**
	 * Alternative without atan at the expense of a slight distorsion on very wideband signals
	 * http://www.embedded.com/design/configurable-systems/4212086/DSP-Tricks--Frequency-demodulation-algorithms-
	 * in addition it needs scaling by instantaneous magnitude squared and volume (0..10) adjustment factor
	 */
	Real phaseDiscriminator2(const Complex& sample, Real msq)
	{
		Real ip = sample.real() - m_m2Sample.real();
		Real qp = sample.imag() - m_m2Sample.imag();
		Real h1 = m_m1Sample.real() * qp;
		Real h2 = m_m1Sample.imag() * ip;

		m_m2Sample = m_m1Sample;
		m_m1Sample = sample;

		return ((h1 - h2) / (msq * M_PI)) * m_fmScaling;
	}

	void apply();
};

#endif // INCLUDE_BFMDEMOD_H