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ofdm.cpp

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00001 
00032 #include <itpp/comm/ofdm.h>
00033 #include <itpp/base/specmat.h>
00034 #include <itpp/base/operators.h>
00035 #include <itpp/signal/transforms.h>
00036 
00037 
00038 namespace itpp
00039 {
00040 
00041 OFDM::OFDM(int inNfft, int inNcp, int inNupsample)
00042 {
00043   set_parameters(inNfft, inNcp, inNupsample);
00044 }
00045 
00046 void OFDM::set_parameters(const int inNfft, const int inNcp, const int inNupsample)
00047 {
00048   it_assert(inNfft >= 2, "OFDM: Nfft must be >=2.");
00049   it_assert(inNcp >= 0 && inNcp <= inNfft, "OFDM: Ncp must be >=0 and <=Nfft.");
00050   it_assert(inNupsample >= 1 && inNupsample <= 100, "OFDM: Ncp must be >=1 and <=100.");
00051   Nfft = inNfft;
00052   Ncp = inNcp;
00053   Nupsample = inNupsample;
00054   norm_factor = std::sqrt(static_cast<double>(Nupsample * Nfft * Nfft) / (Nfft + Ncp));
00055   setup_done = true;
00056 }
00057 
00058 void OFDM::modulate(const cvec &input, cvec &output)
00059 {
00060   it_assert(setup_done == true, "OFDM::modulate: You must set the length of the FFT and the cyclic prefix!");
00061   const int N = input.length() / Nfft;
00062   it_assert(N*Nfft == input.length(), "OFDM::modulate: Length of input vector is not a multiple of Nfft.");
00063 
00064   output.set_length(Nupsample*N*(Nfft + Ncp));
00065   cvec outtemp(Nfft);
00066 
00067   for (int i = 0; i < N; i++) {
00068     outtemp = ifft(concat(input.mid(i * Nfft, Nfft / 2), zeros_c(Nfft * (Nupsample - 1)),
00069                           input.mid(i * Nfft + Nfft / 2, Nfft / 2))) * norm_factor;
00070     output.replace_mid(Nupsample*(Nfft + Ncp)*i, concat(outtemp.right(Nupsample*Ncp), outtemp));
00071   }
00072 }
00073 
00074 cvec OFDM::modulate(const cvec &input)
00075 {
00076   cvec output;
00077   modulate(input, output);
00078   return output;
00079 }
00080 
00081 void OFDM::demodulate(const cvec& input, cvec &output)
00082 {
00083   it_assert(setup_done == true, "OFDM::demodulate: You must set the length of the FFT and the cyclic prefix!");
00084   const int N = input.length() / (Nfft + Ncp) / Nupsample;
00085   it_assert(Nupsample*N*(Nfft + Ncp) == input.length(), "OFDM: Length of input vector is not a multiple of Nfft+Ncp.");
00086 
00087   output.set_length(N*Nfft);
00088   // normalize also taking the energy loss into the cyclic prefix into account
00089   for (int i = 0; i < N; i++) {
00090     cvec x = fft(input.mid(Nupsample * (i * (Nfft + Ncp) + Ncp), Nupsample * Nfft));
00091     output.replace_mid(Nfft*i, concat(x.left(Nfft / 2), x.right(Nfft / 2)) / norm_factor);
00092   }
00093 }
00094 
00095 cvec OFDM::demodulate(const cvec &input)
00096 {
00097   cvec output;
00098   demodulate(input, output);
00099   return output;
00100 }
00101 
00102 } //namespace itpp
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