00001 00031 #include <itpp/comm/ofdm.h> 00032 #include <itpp/base/specmat.h> 00033 #include <itpp/base/operators.h> 00034 #include <itpp/signal/transforms.h> 00035 00036 00037 namespace itpp 00038 { 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 { 00047 it_assert(inNfft >= 2, "OFDM: Nfft must be >=2."); 00048 it_assert(inNcp >= 0 && inNcp <= inNfft, "OFDM: Ncp must be >=0 and <=Nfft."); 00049 it_assert(inNupsample >= 1 && inNupsample <= 100, "OFDM: Ncp must be >=1 and <=100."); 00050 Nfft = inNfft; 00051 Ncp = inNcp; 00052 Nupsample = inNupsample; 00053 norm_factor = std::sqrt(static_cast<double>(Nupsample * Nfft * Nfft) / (Nfft + Ncp)); 00054 setup_done = true; 00055 } 00056 00057 void OFDM::modulate(const cvec &input, cvec &output) 00058 { 00059 it_assert(setup_done == true, "OFDM::modulate: You must set the length of the FFT and the cyclic prefix!"); 00060 const int N = input.length() / Nfft; 00061 it_assert(N*Nfft == input.length(), "OFDM::modulate: Length of input vector is not a multiple of Nfft."); 00062 00063 output.set_length(Nupsample*N*(Nfft + Ncp)); 00064 cvec outtemp(Nfft); 00065 00066 for (int i = 0; i < N; i++) { 00067 outtemp = ifft(concat(input.mid(i * Nfft, Nfft / 2), zeros_c(Nfft * (Nupsample - 1)), 00068 input.mid(i * Nfft + Nfft / 2, Nfft / 2))) * norm_factor; 00069 output.replace_mid(Nupsample*(Nfft + Ncp)*i, concat(outtemp.right(Nupsample*Ncp), outtemp)); 00070 } 00071 } 00072 00073 cvec OFDM::modulate(const cvec &input) 00074 { 00075 cvec output; 00076 modulate(input, output); 00077 return output; 00078 } 00079 00080 void OFDM::demodulate(const cvec& input, cvec &output) 00081 { 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 { 00096 cvec output; 00097 demodulate(input, output); 00098 return output; 00099 } 00100 00101 } //namespace itpp
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