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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