mirror of
https://github.com/f4exb/sdrangel.git
synced 2024-11-03 15:31:15 -05:00
122 lines
4.4 KiB
C++
122 lines
4.4 KiB
C++
///////////////////////////////////////////////////////////////////////////////////
|
|
// Copyright (C) 2015 Edouard Griffiths, F4EXB //
|
|
// Copyright (C) 2020 Jon Beniston, M7RCE //
|
|
// //
|
|
// 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 //
|
|
// (at your option) any later version. //
|
|
// //
|
|
// 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_GAUSSIAN_H
|
|
#define INCLUDE_GAUSSIAN_H
|
|
|
|
#include <math.h>
|
|
#include "dsp/dsptypes.h"
|
|
|
|
// Standard values for bt
|
|
#define GAUSSIAN_BT_BLUETOOTH 0.5
|
|
#define GAUSSIAN_BT_GSM 0.3
|
|
#define GAUSSIAN_BT_CCSDS 0.25
|
|
#define GAUSSIAN_BT_802_15_4 0.5
|
|
#define GAUSSIAN_BT_AIS 0.5
|
|
|
|
// Gaussian low-pass filter for pulse shaping
|
|
// https://onlinelibrary.wiley.com/doi/pdf/10.1002/9780470041956.app2
|
|
// Unlike raisedcosine.h, this should be feed NRZ values rather than impulse stream, as described here:
|
|
// https://www.mathworks.com/matlabcentral/answers/107231-why-does-the-pulse-shape-generated-by-gaussdesign-differ-from-that-used-in-the-comm-gmskmodulator-ob
|
|
template <class Type> class Gaussian {
|
|
public:
|
|
Gaussian() : m_ptr(0) { }
|
|
|
|
// bt - 3dB bandwidth symbol time product
|
|
// symbolSpan - number of symbols over which the filter is spread
|
|
// samplesPerSymbol - number of samples per symbol
|
|
void create(double bt, int symbolSpan, int samplesPerSymbol)
|
|
{
|
|
int nTaps = symbolSpan * samplesPerSymbol + 1;
|
|
int i;
|
|
|
|
// check constraints
|
|
if(!(nTaps & 1)) {
|
|
qDebug("Gaussian filter has to have an odd number of taps");
|
|
nTaps++;
|
|
}
|
|
|
|
// make room
|
|
m_samples.resize(nTaps);
|
|
for(int i = 0; i < nTaps; i++)
|
|
m_samples[i] = 0;
|
|
m_ptr = 0;
|
|
m_taps.resize(nTaps / 2 + 1);
|
|
|
|
// See eq B.2 - this is alpha over Ts
|
|
double alpha_t = std::sqrt(std::log(2.0) / 2.0) / (bt);
|
|
double sqrt_pi_alpha_t = std::sqrt(M_PI) / alpha_t;
|
|
|
|
// calculate filter taps
|
|
for(i = 0; i < nTaps / 2 + 1; i++)
|
|
{
|
|
double t = (i - (nTaps / 2)) / (double)samplesPerSymbol;
|
|
|
|
// See eq B.5
|
|
m_taps[i] = sqrt_pi_alpha_t * std::exp(-std::pow(t * M_PI / alpha_t, 2.0));
|
|
}
|
|
|
|
// normalize
|
|
double sum = 0;
|
|
for(i = 0; i < (int)m_taps.size() - 1; i++)
|
|
sum += m_taps[i] * 2;
|
|
sum += m_taps[i];
|
|
for(i = 0; i < (int)m_taps.size(); i++)
|
|
m_taps[i] /= sum;
|
|
}
|
|
|
|
Type filter(Type sample)
|
|
{
|
|
Type acc = 0;
|
|
unsigned int n_samples = m_samples.size();
|
|
unsigned int n_taps = m_taps.size() - 1;
|
|
unsigned int a = m_ptr;
|
|
unsigned int b = a == n_samples - 1 ? 0 : a + 1;
|
|
|
|
m_samples[m_ptr] = sample;
|
|
|
|
for (unsigned int i = 0; i < n_taps; ++i)
|
|
{
|
|
acc += (m_samples[a] + m_samples[b]) * m_taps[i];
|
|
|
|
a = (a == 0) ? n_samples - 1 : a - 1;
|
|
b = (b == n_samples - 1) ? 0 : b + 1;
|
|
}
|
|
|
|
acc += m_samples[a] * m_taps[n_taps];
|
|
|
|
m_ptr = (m_ptr == n_samples - 1) ? 0 : m_ptr + 1;
|
|
|
|
return acc;
|
|
}
|
|
/*
|
|
void printTaps()
|
|
{
|
|
for (int i = 0; i < m_taps.size(); i++)
|
|
printf("%.4f ", m_taps[i]);
|
|
printf("\n");
|
|
}
|
|
*/
|
|
private:
|
|
std::vector<Real> m_taps;
|
|
std::vector<Type> m_samples;
|
|
unsigned int m_ptr;
|
|
};
|
|
|
|
#endif // INCLUDE_GAUSSIAN_H
|