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| -rw-r--r-- | src/PAPRStats.cpp | 146 | ||||
| -rw-r--r-- | src/PAPRStats.h | 76 |
2 files changed, 222 insertions, 0 deletions
diff --git a/src/PAPRStats.cpp b/src/PAPRStats.cpp new file mode 100644 index 0000000..bf6acc4 --- /dev/null +++ b/src/PAPRStats.cpp @@ -0,0 +1,146 @@ +/* + Copyright (C) 2005, 2006, 2007, 2008, 2009, 2010, 2011 Her Majesty + the Queen in Right of Canada (Communications Research Center Canada) + + Copyright (C) 2017 + Matthias P. Braendli, matthias.braendli@mpb.li + + http://opendigitalradio.org + */ +/* + This file is part of ODR-DabMod. + + ODR-DabMod 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, either version 3 of the + License, or (at your option) any later version. + + ODR-DabMod 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 for more details. + + You should have received a copy of the GNU General Public License + along with ODR-DabMod. If not, see <http://www.gnu.org/licenses/>. + */ + +#include "PAPRStats.h" +#include <numeric> +#include <cmath> +#if defined(TEST) +/* compile with g++ -std=c++11 -Wall -DTEST PAPRStats.cpp -o paprtest */ +# include <iostream> +#endif + + +PAPRStats::PAPRStats(size_t num_blocks_to_accumulate) : + m_num_blocks_to_accumulate(num_blocks_to_accumulate) +{ +} + +void PAPRStats::process_block(const complexf* data, size_t data_len) +{ + double norm_peak = 0; + double rms2 = 0; + + for (size_t i = 0; i < data_len; i++) { + const double x_norm = std::norm(data[i]); + + if (x_norm > norm_peak) { + norm_peak = x_norm; + } + + rms2 += x_norm; + } + + rms2 /= data_len; + +#if defined(TEST) + std::cerr << "Accumulating peak " << norm_peak << + " rms2 " << rms2 << std::endl; +#endif + + m_squared_peaks.push_back(norm_peak); + m_squared_mean.push_back(rms2); + + if (m_squared_mean.size() > m_num_blocks_to_accumulate) { + m_squared_mean.pop_front(); + m_squared_peaks.pop_front(); + } +} + +double PAPRStats::calculate_papr() +{ + if (m_squared_mean.size() < m_num_blocks_to_accumulate) { + return 0; + } + + if (m_squared_mean.size() != m_squared_peaks.size()) { + throw std::logic_error("Invalid PAPR measurement sizes"); + } + + double peak = 0; + double rms2 = 0; + for (size_t i = 0; i < m_squared_peaks.size(); i++) { + if (m_squared_peaks[i] > peak) { + peak = m_squared_peaks[i]; + } + + rms2 += m_squared_mean[i]; + } + + // This assumes all blocks given to process have the same length + rms2 /= m_squared_peaks.size(); + +#if defined(TEST) + std::cerr << "Calculate peak " << peak << + " rms2 " << rms2 << std::endl; +#endif + + return 10.0 * std::log10(peak / rms2); +} + +#if defined(TEST) +/* Test python code: +import numpy as np +vec = 0.5 * np.exp(np.complex(0, 0.3) * np.arange(40)) +vec[26] = 10.0 * vec[26] +rms = np.mean(vec * np.conj(vec)).real +peak = np.amax(vec * np.conj(vec)).real +print("rms {}".format(rms)) +print("peak {}".format(peak)) +print(10. * np.log10(peak / rms)) +*/ +int main(int argc, char **argv) +{ + using namespace std; + vector<complexf> vec(40); + + for (size_t i = 0; i < vec.size(); i++) { + vec[i] = polar(0.5, 0.3 * i); + if (i == 26) { + vec[i] *= 10; + } + cout << " " << vec[i]; + } + cout << endl; + + PAPRStats stats(4); + + for (size_t i = 0; i < 3; i++) { + stats.process_block(vec.data(), vec.size()); + } + + const auto papr0 = stats.calculate_papr(); + if (papr0 != 0) { + cerr << "Expected 0, got " << papr0 << endl; + } + + stats.process_block(vec.data(), vec.size()); + + const auto papr1 = stats.calculate_papr(); + cout << "PAPR = " << papr1 << " dB" << endl; + +} + +#endif diff --git a/src/PAPRStats.h b/src/PAPRStats.h new file mode 100644 index 0000000..9463a3d --- /dev/null +++ b/src/PAPRStats.h @@ -0,0 +1,76 @@ +/* + Copyright (C) 2005, 2006, 2007, 2008, 2009, 2010, 2011 Her Majesty + the Queen in Right of Canada (Communications Research Center Canada) + + Copyright (C) 2017 + Matthias P. Braendli, matthias.braendli@mpb.li + + http://opendigitalradio.org + */ +/* + This file is part of ODR-DabMod. + + ODR-DabMod 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, either version 3 of the + License, or (at your option) any later version. + + ODR-DabMod 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 for more details. + + You should have received a copy of the GNU General Public License + along with ODR-DabMod. If not, see <http://www.gnu.org/licenses/>. + */ + +#pragma once + +#ifdef HAVE_CONFIG_H +# include "config.h" +#endif + +#include <cstddef> +#include <vector> +#include <deque> +#include <complex> + +typedef std::complex<float> complexf; + +/* Helper class to calculate Peak-to-average-power ratio. + * Definition of PAPR: + * + * PAPR_dB = 10 * log_10 ( abs(x_peak)^2 / x_rms^2 ) + * + * with abs(x_peak) the peak amplitude of the signal, and + * x_rms the Root Mean Squared. + * + * x_rms^2 = 1/n * Sum abs(x_n)^2 + * = 1/n * Sum norm(x_n) + * + * Given that peaks are rare in a DAB signal, we want to accumulate + * several seconds worth of samples to do our calculation. + */ +class PAPRStats +{ + public: + PAPRStats(size_t num_blocks_to_accumulate); + + /* Push in a new block of samples to measure. calculate_papr() + * assumes all blocks have the same size. + */ + void process_block(const complexf* data, size_t data_len); + + /* Returns PAPR in dB if enough blocks were processed, or + * 0 otherwise. + */ + double calculate_papr(void); + + private: + size_t m_num_blocks_to_accumulate; + std::deque<double> m_squared_peaks; + std::deque<double> m_squared_mean; +}; + + + |