PhaseDiscriminators Class Reference

#include <phasediscri.h>

Public Member Functions
void	reset ()
void	setFMScaling (Real fmScaling)
Real	phaseDiscriminator (const Complex &sample)
Real	phaseDiscriminatorDelta (const Complex &sample, double &magsq, Real &fmDev)
Real	phaseDiscriminator2 (const Complex &sample)
Real	phaseDiscriminator3 (const Complex &sample, long double &magsq, Real &fltVal)

Private Member Functions
float	atan2_approximation1 (float y, float x)
float	atan2_approximation2 (float y, float x)

Private Attributes
Complex	m_m1Sample
Complex	m_m2Sample
Real	m_fmScaling
Real	m_fltPreviousI
Real	m_fltPreviousQ
Real	m_fltPreviousI2
Real	m_fltPreviousQ2
Real	m_prevArg

Detailed Description

Definition at line 27 of file phasediscri.h.

Member Function Documentation

atan2_approximation1()

float PhaseDiscriminators::atan2_approximation1 ( float  y, float  x  )

inlineprivate

Definition at line 142 of file phasediscri.h.

References M_PI.

    {
        //http://pubs.opengroup.org/onlinepubs/009695399/functions/atan2.html
        //Volkan SALMA

        const float ONEQTR_PI = M_PI / 4.0;
        const float THRQTR_PI = 3.0 * M_PI / 4.0;
        float r, angle;
        float abs_y = std::fabs(y) + 1e-10f;      // kludge to prevent 0/0 condition
        if ( x < 0.0f )
        {
            r = (x + abs_y) / (abs_y - x);
            angle = THRQTR_PI;
        }
        else
        {
            r = (x - abs_y) / (x + abs_y);
            angle = ONEQTR_PI;
        }
        angle += (0.1963f * r * r - 0.9817f) * r;
        if ( y < 0.0f )
            return( -angle );     // negate if in quad III or IV
        else
            return( angle );


    }

atan2_approximation2()

float PhaseDiscriminators::atan2_approximation2 ( float  y, float  x  )

inlineprivate

Definition at line 173 of file phasediscri.h.

References PI_FLOAT, and PIBY2_FLOAT.

Referenced by phaseDiscriminatorDelta().

    {
        if ( x == 0.0f )
        {
            if ( y > 0.0f ) return PIBY2_FLOAT;
            if ( y == 0.0f ) return 0.0f;
            return -PIBY2_FLOAT;
        }
        float atan;
        float z = y/x;
        if ( std::fabs( z ) < 1.0f )
        {
            atan = z/(1.0f + 0.28f*z*z);
            if ( x < 0.0f )
            {
                if ( y < 0.0f ) return atan - PI_FLOAT;
                return atan + PI_FLOAT;
            }
        }
        else
        {
            atan = PIBY2_FLOAT - z/(z*z + 0.28f);
            if ( y < 0.0f ) return atan - PI_FLOAT;
        }
        return atan;
    }

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phaseDiscriminator()

Real PhaseDiscriminators::phaseDiscriminator ( const Complex &  sample )

inline

Standard discriminator using atan2. On modern processors this is as efficient as the non atan2 one. This is better for high fidelity.

Definition at line 51 of file phasediscri.h.

References m_fmScaling, m_m1Sample, and M_PI.

Referenced by DSDDemod::feed(), UDPSink::feed(), and BFMDemod::feed().

    {
        Complex d(std::conj(m_m1Sample) * sample);
        m_m1Sample = sample;
        return (std::atan2(d.imag(), d.real()) / M_PI) * m_fmScaling;
    }

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phaseDiscriminator2()

Real PhaseDiscriminators::phaseDiscriminator2 ( const Complex &  sample )

inline

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

Definition at line 86 of file phasediscri.h.

References m_fmScaling, m_m1Sample, and m_m2Sample.

    {
        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) / M_PI_2) * m_fmScaling;
        return (h1 - h2) * m_fmScaling;
    }

phaseDiscriminator3()

Real PhaseDiscriminators::phaseDiscriminator3 ( const Complex &  sample, long double &  magsq, Real &  fltVal  )

inline

Second alternative

Definition at line 103 of file phasediscri.h.

References m_fltPreviousI, m_fltPreviousI2, m_fltPreviousQ, m_fltPreviousQ2, m_fmScaling, and sqrt().

    {
        Real fltI = sample.real();
        Real fltQ = sample.imag();
        double fltNorm;
        Real fltNormI;
        Real fltNormQ;
        //Real fltVal;

        magsq = fltI*fltI + fltQ*fltQ;
        fltNorm = std::sqrt(magsq);

        fltNormI= fltI/fltNorm;
        fltNormQ= fltQ/fltNorm;

        fltVal = m_fltPreviousI*(fltNormQ - m_fltPreviousQ2);
        fltVal -= m_fltPreviousQ*(fltNormI - m_fltPreviousI2);
        fltVal += 2.0f;
        fltVal /= 4.0f; // normally it is /4

        m_fltPreviousQ2 = m_fltPreviousQ;
        m_fltPreviousI2 = m_fltPreviousI;

        m_fltPreviousQ = fltNormQ;
        m_fltPreviousI = fltNormI;

        return fltVal * m_fmScaling;
    }

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phaseDiscriminatorDelta()

Real PhaseDiscriminators::phaseDiscriminatorDelta ( const Complex &  sample, double &  magsq, Real &  fmDev  )

inline

Discriminator with phase detection using atan2 and frequency by derivation. This yields a precise deviation to sample rate ratio: Sample rate => +/-1.0

Definition at line 62 of file phasediscri.h.

References atan2_approximation2(), m_fmScaling, M_PI, and m_prevArg.

Referenced by ATVDemod::demod(), WFMDemod::feed(), and NFMDemod::processOneSample().

    {
        Real fltI = sample.real();
        Real fltQ = sample.imag();
        magsq = fltI*fltI + fltQ*fltQ;

        Real curArg = atan2_approximation2((float) fltQ, (float) fltI);
        fmDev = (curArg - m_prevArg) / M_PI;
        m_prevArg = curArg;

        if (fmDev < -1.0f) {
            fmDev += 2.0f;
        } else if (fmDev > 1.0f) {
            fmDev -= 2.0f;
        }

        return fmDev * m_fmScaling;
    }

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reset()

void PhaseDiscriminators::reset ( )

inline

Reset stored values

Definition at line 33 of file phasediscri.h.

References m_m1Sample, and m_m2Sample.

Referenced by WFMDemod::start(), DSDDemod::start(), UDPSink::start(), NFMDemod::start(), and BFMDemod::start().

    {
        m_m1Sample = 0;
        m_m2Sample = 0;
    }

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setFMScaling()

void PhaseDiscriminators::setFMScaling ( Real  fmScaling )

inline

Scaling factor so that resulting excursion maps to [-1,+1]

Definition at line 42 of file phasediscri.h.

References m_fmScaling.

Referenced by WFMDemod::applyChannelSettings(), BFMDemod::applyChannelSettings(), WFMDemod::applySettings(), UDPSink::applySettings(), NFMDemod::applySettings(), DSDDemod::applySettings(), BFMDemod::applySettings(), ATVDemod::applySettings(), ATVDemod::ATVDemod(), BFMDemod::BFMDemod(), UDPSink::UDPSink(), and WFMDemod::WFMDemod().

    {
        m_fmScaling = fmScaling;
    }

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Member Data Documentation

m_fltPreviousI

Real PhaseDiscriminators::m_fltPreviousI

private

Definition at line 136 of file phasediscri.h.

Referenced by phaseDiscriminator3().

m_fltPreviousI2

Real PhaseDiscriminators::m_fltPreviousI2

private

Definition at line 138 of file phasediscri.h.

Referenced by phaseDiscriminator3().

m_fltPreviousQ

Real PhaseDiscriminators::m_fltPreviousQ

private

Definition at line 137 of file phasediscri.h.

Referenced by phaseDiscriminator3().

m_fltPreviousQ2

Real PhaseDiscriminators::m_fltPreviousQ2

private

Definition at line 139 of file phasediscri.h.

Referenced by phaseDiscriminator3().

m_fmScaling

Real PhaseDiscriminators::m_fmScaling

private

Definition at line 135 of file phasediscri.h.

Referenced by phaseDiscriminator(), phaseDiscriminator2(), phaseDiscriminator3(), phaseDiscriminatorDelta(), and setFMScaling().

m_m1Sample

Complex PhaseDiscriminators::m_m1Sample

private

Definition at line 133 of file phasediscri.h.

Referenced by phaseDiscriminator(), phaseDiscriminator2(), and reset().

m_m2Sample

Complex PhaseDiscriminators::m_m2Sample

private

Definition at line 134 of file phasediscri.h.

Referenced by phaseDiscriminator2(), and reset().

m_prevArg

Real PhaseDiscriminators::m_prevArg

private

Definition at line 140 of file phasediscri.h.

Referenced by phaseDiscriminatorDelta().

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The documentation for this class was generated from the following file:

• sdrbase/dsp/phasediscri.h