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/*!
* \file
* \brief Implementation of an Orthogonal Frequency Division Multiplex
* (OFDM) class
* \author Pal Frenger, Anders Persson and Tony Ottosson
*
* -------------------------------------------------------------------------
*
* Copyright (C) 1995-2010 (see AUTHORS file for a list of contributors)
*
* This file is part of IT++ - a C++ library of mathematical, signal
* processing, speech processing, and communications classes and functions.
*
* IT++ 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.
*
* IT++ 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 IT++. If not, see <http://www.gnu.org/licenses/>.
*
* -------------------------------------------------------------------------
*/
#include <itpp/comm/ofdm.h>
#include <itpp/base/specmat.h>
#include <itpp/base/operators.h>
#include <itpp/signal/transforms.h>
namespace itpp
{
OFDM::OFDM(int inNfft, int inNcp, int inNupsample)
{
set_parameters(inNfft, inNcp, inNupsample);
}
void OFDM::set_parameters(const int inNfft, const int inNcp, const int inNupsample)
{
it_assert(inNfft >= 2, "OFDM: Nfft must be >=2.");
it_assert(inNcp >= 0 && inNcp <= inNfft, "OFDM: Ncp must be >=0 and <=Nfft.");
it_assert(inNupsample >= 1 && inNupsample <= 100, "OFDM: Ncp must be >=1 and <=100.");
Nfft = inNfft;
Ncp = inNcp;
Nupsample = inNupsample;
norm_factor = std::sqrt(static_cast<double>(Nupsample * Nfft * Nfft) / (Nfft + Ncp));
setup_done = true;
}
void OFDM::modulate(const cvec &input, cvec &output)
{
it_assert(setup_done == true, "OFDM::modulate: You must set the length of the FFT and the cyclic prefix!");
const int N = input.length() / Nfft;
it_assert(N*Nfft == input.length(), "OFDM::modulate: Length of input vector is not a multiple of Nfft.");
output.set_length(Nupsample*N*(Nfft + Ncp));
cvec outtemp(Nfft);
for (int i = 0; i < N; i++) {
outtemp = ifft(concat(input.mid(i * Nfft, Nfft / 2), zeros_c(Nfft * (Nupsample - 1)),
input.mid(i * Nfft + Nfft / 2, Nfft / 2))) * norm_factor;
output.replace_mid(Nupsample*(Nfft + Ncp)*i, concat(outtemp.right(Nupsample*Ncp), outtemp));
}
}
cvec OFDM::modulate(const cvec &input)
{
cvec output;
modulate(input, output);
return output;
}
void OFDM::demodulate(const cvec& input, cvec &output)
{
it_assert(setup_done == true, "OFDM::demodulate: You must set the length of the FFT and the cyclic prefix!");
const int N = input.length() / (Nfft + Ncp) / Nupsample;
it_assert(Nupsample*N*(Nfft + Ncp) == input.length(), "OFDM: Length of input vector is not a multiple of Nfft+Ncp.");
output.set_length(N*Nfft);
// normalize also taking the energy loss into the cyclic prefix into account
for (int i = 0; i < N; i++) {
cvec x = fft(input.mid(Nupsample * (i * (Nfft + Ncp) + Ncp), Nupsample * Nfft));
output.replace_mid(Nfft*i, concat(x.left(Nfft / 2), x.right(Nfft / 2)) / norm_factor);
}
}
cvec OFDM::demodulate(const cvec &input)
{
cvec output;
demodulate(input, output);
return output;
}
} //namespace itpp
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