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ofdm.cpp

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