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113 lines
3.6 KiB
C++
113 lines
3.6 KiB
C++
///////////////////////////////////////////////////////////////////////////////////
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// Copyright 2006-2021 Free Software Foundation, Inc. //
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// Copyright (C) 2018 Edouard Griffiths, F4EXB //
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// Copyright (C) 2021 Jon Beniston, M7RCE //
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// //
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// Based on the Costas Loop from GNU Radio //
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// //
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// This program is free software; you can redistribute it and/or modify //
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// it under the terms of the GNU General Public License as published by //
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// the Free Software Foundation as version 3 of the License, or //
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// (at your option) any later version. //
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// //
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// This program is distributed in the hope that it will be useful, //
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// but WITHOUT ANY WARRANTY; without even the implied warranty of //
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// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the //
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// GNU General Public License V3 for more details. //
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// //
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// You should have received a copy of the GNU General Public License //
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// along with this program. If not, see <http://www.gnu.org/licenses/>. //
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///////////////////////////////////////////////////////////////////////////////////
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#include "costasloop.h"
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#include <cmath>
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// Loop bandwidth supposedly ~ 2pi/100 rads/sample
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// pskOrder 2, 4 or 8
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CostasLoop::CostasLoop(float loopBW, unsigned int pskOrder) :
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m_maxFreq(1.0f),
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m_minFreq(-1.0f),
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m_pskOrder(pskOrder)
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{
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computeCoefficients(loopBW);
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reset();
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}
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CostasLoop::~CostasLoop()
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{
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}
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void CostasLoop::reset()
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{
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m_y.real(1.0f);
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m_y.imag(0.0f);
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m_freq = 0.0f;
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m_phase = 0.0f;
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m_freq = 0.0f;
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m_error = 0.0f;
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}
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// 2nd order loop with critical damping
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void CostasLoop::computeCoefficients(float loopBW)
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{
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float damping = sqrtf(2.0f) / 2.0f;
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float denom = (1.0 + 2.0 * damping * loopBW + loopBW * loopBW);
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m_alpha = (4 * damping * loopBW) / denom;
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m_beta = (4 * loopBW * loopBW) / denom;
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}
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void CostasLoop::setSampleRate(unsigned int sampleRate)
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{
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(void) sampleRate;
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reset();
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}
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static float branchlessClip(float x, float clip)
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{
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return 0.5f * (std::abs(x + clip) - std::abs(x - clip));
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}
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// Don't use built-in complex.h multiply to avoid NaN/INF checking
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static void fastComplexMultiply(std::complex<float> &out, const std::complex<float> cc1, const std::complex<float> cc2)
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{
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float o_r, o_i;
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o_r = (cc1.real() * cc2.real()) - (cc1.imag() * cc2.imag());
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o_i = (cc1.real() * cc2.imag()) + (cc1.imag() * cc2.real());
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out.real(o_r);
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out.imag(o_i);
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}
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void CostasLoop::feed(float re, float im)
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{
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std::complex<float> nco(::cosf(-m_phase), ::sinf(-m_phase));
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std::complex<float> in, out;
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in.real(re);
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in.imag(im);
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fastComplexMultiply(out, in, nco);
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switch (m_pskOrder)
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{
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case 2:
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m_error = phaseDetector2(out);
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break;
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case 4:
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m_error = phaseDetector4(out);
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break;
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case 8:
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m_error = phaseDetector8(out);
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break;
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}
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m_error = branchlessClip(m_error, 1.0f);
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advanceLoop(m_error);
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phaseWrap();
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frequencyLimit();
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m_y.real(-nco.real());
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m_y.imag(nco.imag());
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}
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