fun::fft_symbols Class Reference

The fft_symbols block. More...

#include <fft_symbols.h>

Inheritance diagram for fun::fft_symbols:

Public Member Functions
	fft_symbols ()
	Constructor for fft_symbols block. More...
virtual void	work ()
	Signal processing happens here. More...
Public Member Functions inherited from fun::block< tagged_sample, tagged_vector< 64 > >
	block (std::string block_name)
	constructor More...
Public Member Functions inherited from fun::block_base
	block_base (std::string block_name)
	block_base constructor More...

Private Attributes
tagged_vector< 64 >	m_current_vector
	Current vector being filled. More...
int	m_offset
	Offset into the current vector being filled. More...
fft	m_ffft
	Forward FFT. More...

Additional Inherited Members
Public Attributes inherited from fun::block< tagged_sample, tagged_vector< 64 > >
std::vector< tagged_sample >	input_buffer
	input_buffer contains new input items to be consumed More...
std::vector< tagged_vector< 64 > >	output_buffer
	output_buffer is where the output items of the block should be placed More...

Detailed Description

The fft_symbols block.

Inputs tagged_samples from timing_sync block (time domain samples). Outputs tagged_vectors to channel estimator block (frequency domain samples).

This FFT Symbols aligns the input samples into symbols, chops off the cyclic prefixes, and performs a forward FFT on vectorized samples to convert them from time domain to frequency domain symbols.

Definition at line 32 of file fft_symbols.h.

Constructor & Destructor Documentation

fun::fft_symbols::fft_symbols

(

)

Constructor for fft_symbols block.

• Initializations:
  • m_offset -> 0
  • m_ffft -> Instance of 64 point forward fft class

Definition at line 21 of file fft_symbols.cpp.

                             :
        block("fft_symbols"),
        m_offset(0),
        m_ffft(64)
    {
    }

Member Function Documentation

void fun::fft_symbols::work ( )

virtual

Signal processing happens here.

This block removes the cyclic prefix and vectorizes the samples into 64 sample symbols based on the tags marking the frame boundaries. It then performs a 64 point forward fft on each symbol to convert it from time domain to frequency domain.

Implements fun::block< tagged_sample, tagged_vector< 64 > >.

Definition at line 33 of file fft_symbols.cpp.

References fun::fft::forward(), fun::block< tagged_sample, tagged_vector< 64 > >::input_buffer, fun::LTS1, fun::LTS2, fun::LTS_START, m_current_vector, m_ffft, m_offset, fun::NONE, fun::block< tagged_sample, tagged_vector< 64 > >::output_buffer, fun::tagged_vector< N >::samples, and fun::tagged_vector< N >::tag.

    {
        if(input_buffer.size() == 0) return;
        output_buffer.resize(0);

        // Step through the input samples
        for(int x = 0; x < input_buffer.size(); x++)
        {
            // Check if this is the start of a new frame
            if(input_buffer[x].tag == LTS1)
            {
                // Push the current vector to the output buffer if
                // we've written any data to it
                if(m_offset > 15) output_buffer.push_back(m_current_vector);

                // Start a new vector
                m_current_vector.tag = LTS_START;
                m_offset = 16;
            }

            if(input_buffer[x].tag == LTS2)
            {
                m_offset = 16;
            }

            // Copy over samples past the cyclic prefix
            if(m_offset > 15)
            {
                m_current_vector.samples[m_offset - 16] = input_buffer[x].sample;
            }

            // Increment the offset and reset if we're at the end of the symbol
            m_offset++;
            if(m_offset == 80)
            {
                output_buffer.push_back(m_current_vector);
                m_current_vector.tag = NONE;
                m_offset = 0;
            }
        }

        // Perform forward FFT
        for(int x = 0; x < output_buffer.size(); x++)
        {
            m_ffft.forward(output_buffer[x].samples);

        }
    }

Member Data Documentation

tagged_vector<64> fun::fft_symbols::m_current_vector

private

Current vector being filled.

Definition at line 45 of file fft_symbols.h.

Referenced by work().

fft fun::fft_symbols::m_ffft

private

Forward FFT.

Definition at line 55 of file fft_symbols.h.

Referenced by work().

int fun::fft_symbols::m_offset

private

Offset into the current vector being filled.

Definition at line 50 of file fft_symbols.h.

Referenced by work().

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

• /home/benjamin/Documents/fun_ofdm/src/fft_symbols.h
• /home/benjamin/Documents/fun_ofdm/src/fft_symbols.cpp