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