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// samdemod.cpp: implementation of the CSamDemod class.
//
// This class takes I/Q baseband data and performs
// Synchronous AM demodulation
//
// History:
// 2010-09-22 Initial creation MSW
// 2011-03-27 Initial release
// 2011-08-07 Modified FIR filter initialization to force fixed size
// 2013-07-28 Added single/double precision math macros
//////////////////////////////////////////////////////////////////////
//==========================================================================================
// + + + This Software is released under the "Simplified BSD License" + + +
//Copyright 2010 Moe Wheatley. All rights reserved.
//
//Redistribution and use in source and binary forms, with or without modification, are
//permitted provided that the following conditions are met:
//
// 1. Redistributions of source code must retain the above copyright notice, this list of
// conditions and the following disclaimer.
//
// 2. Redistributions in binary form must reproduce the above copyright notice, this list
// of conditions and the following disclaimer in the documentation and/or other materials
// provided with the distribution.
//
//THIS SOFTWARE IS PROVIDED BY Moe Wheatley ``AS IS'' AND ANY EXPRESS OR IMPLIED
//WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND
//FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL Moe Wheatley OR
//CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
//CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
//SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON
//ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
//NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
//ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
//
//The views and conclusions contained in the software and documentation are those of the
//authors and should not be interpreted as representing official policies, either expressed
//or implied, of Moe Wheatley.
//==========================================================================================
#include "samdemod.h"
#include "gui/testbench.h"
#include "dsp/datatypes.h"
#include "dsp/filtercoef.h"
#include <QDebug>
#define DC_ALPHA 0.99 //ALPHA for DC removal filter ~20Hz Fcut with 15625Hz Sample Rate
#define PLL_BW 100.0 //natural frequency ~ loop bandwidth
#define PLL_ZETA .707 //PLL Loop damping factor
#define PLL_LIMIT 1000.0 //+- frequency limit in Hz
/////////////////////////////////////////////////////////////////////////////////
// Construct SAM demod object
/////////////////////////////////////////////////////////////////////////////////
CSamDemod::CSamDemod(TYPEREAL samplerate) : m_SampleRate(samplerate)
{
m_y1 = 0.0;
m_z1 = 0.0;
m_NcoPhase = 0.0;
m_NcoFreq = 0.0;
TYPEREAL norm = K_2PI/m_SampleRate;
m_NcoLLimit = -PLL_LIMIT * norm; //clamp SAM NCO to +-1KHz
m_NcoHLimit = PLL_LIMIT * norm;
m_PllAlpha = 2.0*PLL_ZETA*PLL_BW * norm;
m_PllBeta = (m_PllAlpha * m_PllAlpha)/(4.0*PLL_ZETA*PLL_ZETA);
//create complex lowpass filter pair with LP cuttoff of 5000Hz and transition width of 1000Hz
// 40dB stop band attenuation
m_Fir.InitLPFilter(0, 1.0, 40.0, 4500, 5500,m_SampleRate);
//apply transform to shift the LP filter 5000Hz so now the filter is
// a 0 to 10000Hz Hilbert bandpass filter with 90 degree phase shift
m_Fir.GenerateHBFilter(5000.0);
}
/////////////////////////////////////////////////////////////////////////////////
// Process SAM demod MONO version
/////////////////////////////////////////////////////////////////////////////////
int CSamDemod::ProcessData(int InLength, TYPECPX* pInData, TYPEREAL* pOutData)
{
TYPECPX tmp;
for(int i=0; i<InLength; i++)
{
TYPEREAL Sin = MSIN(m_NcoPhase);
TYPEREAL Cos = MCOS(m_NcoPhase);
//complex multiply input sample by NCO's -sin and cos
tmp.re = Cos * pInData[i].re - Sin * pInData[i].im;
tmp.im = Cos * pInData[i].im + Sin * pInData[i].re;
//find current sample phase after being shifted by NCO frequency
TYPEREAL phzerror = -MATAN2(tmp.im, tmp.re);
//TYPEREAL test = phzerror*100.0;
//g_pTestBench->DisplayData(1, 1.0, &test, m_SampleRate,PROFILE_6);
m_NcoFreq += (m_PllBeta * phzerror); // radians per sampletime
//clamp NCO frequency so doesn't drift out of lock range
if(m_NcoFreq > m_NcoHLimit)
m_NcoFreq = m_NcoHLimit;
else if(m_NcoFreq < m_NcoLLimit)
m_NcoFreq = m_NcoLLimit;
//update NCO phase with new value
m_NcoPhase += (m_NcoFreq + m_PllAlpha * phzerror);
//High pass filter(DC removal) with IIR filter
// H(z) = (1 - z^-1)/(1 - ALPHA*z^-1)
TYPEREAL z0 = tmp.re + (m_z1 * DC_ALPHA); //just use real output for mono
pOutData[i] = (z0 - m_z1);
m_z1 = z0;
}
m_NcoPhase = MFMOD(m_NcoPhase, K_2PI); //keep radian counter bounded
return InLength;
}
/////////////////////////////////////////////////////////////////////////////////
// Process SAM demod STEREO version
/////////////////////////////////////////////////////////////////////////////////
int CSamDemod::ProcessData(int InLength, TYPECPX* pInData, TYPECPX* pOutData)
{
TYPECPX tmp;
for(int i=0; i<InLength; i++)
{
TYPEREAL Sin = MSIN(m_NcoPhase);
TYPEREAL Cos = MCOS(m_NcoPhase);
//complex multiply input sample by NCO's sin and cos
tmp.re = Cos * pInData[i].re - Sin * pInData[i].im;
tmp.im = Cos * pInData[i].im + Sin * pInData[i].re;
//find current sample phase error after being shifted by NCO frequency
TYPEREAL phzerror = -MATAN2(tmp.im, tmp.re);
//TYPEREAL test = phzerror*100.0;
//g_pTestBench->DisplayData(1, 1.0, &test, m_SampleRate,PROFILE_6);
m_NcoFreq += (m_PllBeta * phzerror); // radians per sampletime
//clamp NCO frequency so doesn't drift out of lock range
if(m_NcoFreq > m_NcoHLimit)
m_NcoFreq = m_NcoHLimit;
else if(m_NcoFreq < m_NcoLLimit)
m_NcoFreq = m_NcoLLimit;
//update NCO phase with new value
m_NcoPhase += (m_NcoFreq + m_PllAlpha * phzerror);
//High pass filter(DC removal) with IIR filter
// H(z) = (1 - z^-1)/(1 - ALPHA*z^-1)
TYPEREAL z0 = tmp.re + (m_z1 * DC_ALPHA);
TYPEREAL y0 = tmp.im + (m_y1 * DC_ALPHA);
pOutData[i].re = (z0 - m_z1);
pOutData[i].im = (y0 - m_y1);
m_y1 = y0;
m_z1 = z0;
}
m_NcoPhase = MFMOD(m_NcoPhase, K_2PI); //keep radian counter bounded
//process I/Q with bandpass filter with 90deg phase shift between the I and Q filters
m_Fir.ProcessFilter(InLength, pOutData, pOutData);
for(int i=0; i<InLength; i++)
{
tmp = pOutData[i];
pOutData[i].im = tmp.re - tmp.im; //send upper sideband to (right)channel
pOutData[i].re = tmp.re + tmp.im; //send lower sideband to (left)channel
}
return InLength;
}
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