Added a frequency lock loop

sdrbase/CMakeLists.txt

@@ -34,6 +34,7 @@ set(sdrbase_SOURCES
     dsp/filterrc.cpp
     dsp/filtermbe.cpp
     dsp/filerecord.cpp
+    dsp/freqlockcomplex.cpp
     dsp/interpolator.cpp
     dsp/hbfiltertraits.cpp
     dsp/lowpass.cpp
@@ -124,6 +125,7 @@ set(sdrbase_HEADERS
     dsp/filterrc.h
     dsp/filtermbe.h
     dsp/filerecord.h
+    dsp/freqlockcomplex.h
     dsp/gfft.h
     dsp/iirfilter.h
     dsp/interpolator.h
@@ -271,6 +273,7 @@ include_directories(
     .
     ${CMAKE_SOURCE_DIR}/exports
     ${CMAKE_SOURCE_DIR}/httpserver
+    ${CMAKE_SOURCE_DIR}/kitiirfir
     ${CMAKE_SOURCE_DIR}/qrtplib
     ${CMAKE_SOURCE_DIR}/swagger/sdrangel/code/qt5/client
 )
@@ -278,6 +281,7 @@ include_directories(
 target_link_libraries(sdrbase
     ${QT_LIBRARIES}
     httpserver
+    kitiirfir
     qrtplib
     swagger
 )

sdrbase/dsp/freqlockcomplex.cpp

@@ -0,0 +1,122 @@
+///////////////////////////////////////////////////////////////////////////////////
+// Copyright (C) 2018 F4EXB                                                      //
+// written by Edouard Griffiths                                                  //
+//                                                                               //
+// See: http://liquidsdr.org/blog/pll-howto/                                     //
+// Fixed filter registers saturation                                             //
+// Added order for PSK locking. This brilliant idea actually comes from this     //
+// post: https://www.dsprelated.com/showthread/comp.dsp/36356-1.php              //
+//                                                                               //
+// 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 "freqlockcomplex.h"
+#include "IIRFilterCode.h"
+
+FreqLockComplex::FreqLockComplex() :
+    m_a0(1.0),
+    m_a1(1.0),
+    m_a2(1.0),
+    m_b0(1.0),
+    m_b1(1.0),
+    m_b2(1.0),
+    m_v0(0.0),
+    m_v1(0.0),
+    m_v2(0.0),
+    m_y(1.0, 0.0),
+    m_prod(1.0, 0.0),
+    m_yRe(1.0),
+    m_yIm(0.0),
+    m_freq(0.0),
+    m_phi(0.0),
+    m_iir(0)
+{
+}
+
+FreqLockComplex::~FreqLockComplex()
+{
+    if (m_iir) {
+        delete m_iir;
+    }
+}
+
+void FreqLockComplex::reset()
+{
+    m_v0 = 0.0f;
+    m_v1 = 0.0f;
+    m_v2 = 0.0f;
+    m_y.real(1.0);
+    m_y.imag(0.0);
+    m_prod.real(1.0);
+    m_prod.imag(0.0);
+    m_yRe = 1.0f;
+    m_yIm = 0.0f;
+    m_freq = 0.0f;
+    m_phi = 0.0f;
+}
+
+// wn is in terms of Nyquist. For example, if the sampling frequency = 20 kHz
+// and the 3 dB corner frequency is 1.5 kHz, then OmegaC = 0.15
+// i.e. 100.0 / (SR/2) or 200 / SR for 100 Hz
+void FreqLockComplex::computeCoefficients(float wn)
+{
+    kitiirfir::TIIRFilterParams params;
+
+    params.BW = 0.0;         // For band pass and notch filters - unused here
+    params.Gamma = 0.0;      // For Adjustable Gauss. - unused here
+    params.IIRPassType = kitiirfir::iirLPF;
+    params.NumPoles = 1;
+    params.OmegaC = wn;
+    params.ProtoType = kitiirfir::BUTTERWORTH;
+    params.Ripple = 0.0;     // For Elliptic and Chebyshev - unused here
+    params.StopBanddB = 0.0; // For Elliptic and Inverse Chebyshev - unused here
+    params.dBGain = 0.0;
+
+    kitiirfir::TIIRCoeff coeff = kitiirfir::CalcIIRFilterCoeff(params);
+    float a[3], b[3];
+
+    a[0] = coeff.a0[0];
+    a[1] = coeff.a1[0];
+    a[2] = coeff.a2[0];
+    b[0] = coeff.b0[0];
+    b[1] = coeff.b1[0];
+    b[2] = coeff.b2[0];
+
+    qDebug("FreqLockComplex::computeCoefficients: b: %f %f %f", b[0], b[1], b[2]);
+    qDebug("FreqLockComplex::computeCoefficients: a: %f %f %f", a[0], a[1], a[2]);
+
+    m_iir = new IIRFilter<float, 2>(a, b);
+}
+
+void FreqLockComplex::feed(float re, float im)
+{
+    m_yRe = cos(m_phi);
+    m_yIm = sin(m_phi);
+    std::complex<float> y(m_yRe, m_yIm);
+    std::complex<float> x(re, im);
+
+    std::complex<float> prod = x * m_y;
+
+    // Discriminator: cross * sign(dot) / dt
+    float cross = m_prod.real()*prod.imag() - prod.real()*m_prod.imag();
+    float dot = m_prod.real()*prod.real() + m_prod.imag()*prod.imag();
+    float eF = cross * (dot < 0 ? -1 : 1); // frequency error
+
+    // LPF section
+    float efHat = m_iir->run(eF);
+
+    m_freq = efHat; // correct instantaneous frequency
+    m_phi += efHat; // advance phase with instantaneous frequency
+    m_prod = prod;  // store previous product
+}
+

sdrbase/dsp/freqlockcomplex.h

@@ -0,0 +1,62 @@
+///////////////////////////////////////////////////////////////////////////////////
+// Copyright (C) 2018 F4EXB                                                      //
+// written by Edouard Griffiths                                                  //
+//                                                                               //
+// See: http://liquidsdr.org/blog/pll-howto/                                     //
+// Fixed filter registers saturation                                             //
+// Added order for PSK locking. This brilliant idea actually comes from this     //
+// post: https://www.dsprelated.com/showthread/comp.dsp/36356-1.php              //
+//                                                                               //
+// 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 SDRBASE_DSP_FREQLOCKCOMPLEX_H_
+#define SDRBASE_DSP_FREQLOCKCOMPLEX_H_
+
+#include "dsp/dsptypes.h"
+#include "iirfilter.h"
+#include "export.h"
+
+/** General purpose Phase-locked loop using complex analytic signal input. */
+class SDRBASE_API FreqLockComplex
+{
+public:
+    FreqLockComplex();
+    ~FreqLockComplex();
+
+    void reset();
+    void computeCoefficients(float wn);
+    /** Feed PLL with a new signa sample */
+    void feed(float re, float im);
+
+private:
+    float m_a0;
+    float m_a1;
+    float m_a2;
+    float m_b0;
+    float m_b1;
+    float m_b2;
+    float m_v0;
+    float m_v1;
+    float m_v2;
+    std::complex<float> m_y;
+    std::complex<float> m_prod;
+    float m_yRe;
+    float m_yIm;
+    float m_freq;
+    float m_phi;
+    IIRFilter<float, 2> *m_iir;
+};
+
+
+#endif /* SDRBASE_DSP_FREQLOCKCOMPLEX_H_ */