The fft class. More...

#include <fft.h>

Public Member Functions
	fft (int fft_length)
	Constructor for fft object. More...

void	forward (std::complex< double > data[64])
	In place 64 point forward FFT. More...

void	inverse (std::vector< std::complex< double > > &data)
	In place inverse FFT of input data. More...

Private Attributes
int	m_fft_length
	Length of FFT. In 802.11a it is always a 64 Point FFT since There are 64 subcarriers. More...

fftw_complex *	m_fftw_in_forward
	Forward input buffer for use by fftw3 library. More...

fftw_complex *	m_fftw_out_forward
	Forward output buffer for use by fftw3 library. More...

fftw_complex *	m_fftw_in_inverse
	Inverse input buffer for use by fftw3 library. More...

fftw_complex *	m_fftw_out_inverse
	Inverse output buffer for use by fftw3 library. More...

fftw_plan	m_fftw_plan_forward
	Forward FFT plan for use by fftw3 library. More...

fftw_plan	m_fftw_plan_inverse
	Inverse FFT plan for use by fftw3 library. More...

Static Private Attributes
static const int	fft_map [64]
	Mapping to/from FFT order. More...

Detailed Description

The fft class.

This class contains is a wrapper for the fftw3 library and contains the functions and necessary parameters for performing the IFFTs and FFTs in the transmit and receive chains respectively.

Definition at line 24 of file fft.h.

Constructor & Destructor Documentation

fun::fft::fft ( int fft_length)

Constructor for fft object.

Parameters

fft_length length of FFT - i.e. 64 point FFT

-Initializations:

m_fft_length -> 64 because we always deal with 64 point FFTs since there are 64 OFDM subcarriers

Definition at line 30 of file fft.cpp.

References m_fft_length, m_fftw_in_forward, m_fftw_in_inverse, m_fftw_out_forward, m_fftw_out_inverse, m_fftw_plan_forward, and m_fftw_plan_inverse.

                            :
         m_fft_length(fft_length)
     {
         // Allocate the FFT buffers
         m_fftw_in_forward = (fftw_complex *)fftw_malloc(sizeof(fftw_complex) * m_fft_length);
         m_fftw_out_forward = (fftw_complex *)fftw_malloc(sizeof(fftw_complex) * m_fft_length);
         m_fftw_in_inverse = (fftw_complex *)fftw_malloc(sizeof(fftw_complex) * m_fft_length);
         m_fftw_out_inverse = (fftw_complex *)fftw_malloc(sizeof(fftw_complex) * m_fft_length);
         m_fftw_plan_forward = fftw_plan_dft_1d(m_fft_length, m_fftw_in_forward, m_fftw_out_forward, FFTW_FORWARD, FFTW_MEASURE);
         m_fftw_plan_inverse = fftw_plan_dft_1d(m_fft_length, m_fftw_in_inverse, m_fftw_out_inverse, FFTW_BACKWARD, FFTW_MEASURE);
     }

Member Function Documentation

void fun::fft::forward ( std::complex< double > data[64])

In place 64 point forward FFT.

Parameters

data	Array of 64 complex samples in time domain to be converted to frequency domain.

This function performs a single in-place 64 point FFT on the 64 complex data samples. The user must loop over time-domain signal and pass each 64 sample symbol to this function individually. This function handles the shifting from all positive (0-63) indexing to positive & negative frequency indexing.

Definition at line 50 of file fft.cpp.

References fft_map, m_fft_length, m_fftw_in_forward, m_fftw_out_forward, and m_fftw_plan_forward.

Referenced by fun::fft_symbols::work().

     {
         memcpy(m_fftw_in_forward, &data[0], m_fft_length * sizeof(std::complex<double>));
         fftw_execute(m_fftw_plan_forward);
 
         for(int s = 0; s < 64; s++)
         {
             memcpy(&data[s], &m_fftw_out_forward[fft_map[s]], sizeof(std::complex<double>));
         }
     }

void fun::fft::inverse ( std::vector< std::complex< double > > & data)

In place inverse FFT of input data.

Parameters

data	Vector of complex doubles in frequency domain to be converted to time domain. The length of the data vector must be an integer multiple of m_fft_length.

This function loops over the input vector (which must be an integer multiple of 64) and performs in-place 64 point IFFTs on each consecutive 64 sample chunk of the input vector. This function handles the shifting from positive & negative frequency (-32 to 31) indexing to all positive (0 to 63) indexing. This function also scales the output by 1/64 to be consistent with the IFFT function.

Definition at line 68 of file fft.cpp.

References fft_map, m_fft_length, m_fftw_in_inverse, m_fftw_out_inverse, and m_fftw_plan_inverse.

Referenced by fun::frame_builder::build_frame().

     {
         assert(data.size() % m_fft_length == 0);
 
         // Run the IFFT on each m_fft_length samples
         for(int x = 0; x < data.size(); x += m_fft_length)
         {
             if(m_fft_length == 64)
             {
                 for(int s = 0; s < 64; s++)
                 {
                     memcpy(&m_fftw_in_inverse[s], &data[x + fft_map[s]], sizeof(std::complex<double>));
                 }
             }
             else
             {
                 memcpy(&m_fftw_in_inverse[0], &data[x], m_fft_length * sizeof(std::complex<double>));
             }
 
             fftw_execute(m_fftw_plan_inverse);
             memcpy(&data[x], m_fftw_out_inverse, m_fft_length * sizeof(std::complex<double>));
         }
 
         // Scale by 1/fft_length
         for(int x = 0; x < data.size(); x++)
         {
             data[x] /= m_fft_length;
         }
     }

Member Data Documentation

const int fun::fft::fft_map

staticprivate

Initial value:

=
    {
      32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63,
      0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31
    }

Mapping to/from FFT order.

This map shifts the subcarriers so that instead of being thought of sequentially from 0-63 they can be thought of as positive and negative frequencies which is the ordering that the FFTW3 library uses.

Definition at line 55 of file fft.h.

Referenced by forward(), and inverse().

int fun::fft::m_fft_length

private

Length of FFT. In 802.11a it is always a 64 Point FFT since There are 64 subcarriers.

Definition at line 61 of file fft.h.

Referenced by fft(), forward(), and inverse().

fftw_complex* fun::fft::m_fftw_in_forward

private

Forward input buffer for use by fftw3 library.

Definition at line 66 of file fft.h.

Referenced by fft(), and forward().

fftw_complex* fun::fft::m_fftw_in_inverse

private

Inverse input buffer for use by fftw3 library.

Definition at line 76 of file fft.h.

Referenced by fft(), and inverse().

fftw_complex* fun::fft::m_fftw_out_forward

private

Forward output buffer for use by fftw3 library.

Definition at line 71 of file fft.h.

Referenced by fft(), and forward().

fftw_complex* fun::fft::m_fftw_out_inverse

private

Inverse output buffer for use by fftw3 library.

Definition at line 81 of file fft.h.

Referenced by fft(), and inverse().

fftw_plan fun::fft::m_fftw_plan_forward

private

Forward FFT plan for use by fftw3 library.

Definition at line 86 of file fft.h.

Referenced by fft(), and forward().

fftw_plan fun::fft::m_fftw_plan_inverse

private

Inverse FFT plan for use by fftw3 library.

Definition at line 91 of file fft.h.

Referenced by fft(), and inverse().

The documentation for this class was generated from the following files:

/home/benjamin/Documents/fun_ofdm/src/fft.h
/home/benjamin/Documents/fun_ofdm/src/fft.cpp

Public Member Functions

Private Attributes

Static Private Attributes

Detailed Description

Constructor & Destructor Documentation

Member Function Documentation

Member Data Documentation