digital_ofdm_frame_acquisition Class Reference

take a vector of complex constellation points in from an FFT and performs a correlation and equalization.This block takes the output of an FFT of a received OFDM symbol and finds the start of a frame based on two known symbols. It also looks at the surrounding bins in the FFT output for the correlation in case there is a large frequency shift in the data. This block assumes that the fine frequency shift has already been corrected and that the samples fall in the middle of one FFT bin. More...

#include <digital_ofdm_frame_acquisition.h>

Inheritance diagram for digital_ofdm_frame_acquisition:

List of all members.

Public Member Functions
float	snr ()
	Return an estimate of the SNR of the channel.
	~digital_ofdm_frame_acquisition (void)
int	general_work (int noutput_items, gr_vector_int &ninput_items, gr_vector_const_void_star &input_items, gr_vector_void_star &output_items)
	compute output items from input items
Protected Member Functions
	digital_ofdm_frame_acquisition (unsigned int occupied_carriers, unsigned int fft_length, unsigned int cplen, const std::vector< gr_complex > &known_symbol, unsigned int max_fft_shift_len)
Friends
DIGITAL_API digital_ofdm_frame_acquisition_sptr	digital_make_ofdm_frame_acquisition (unsigned int occupied_carriers, unsigned int fft_length, unsigned int cplen, const std::vector< gr_complex > &known_symbol, unsigned int max_fft_shift_len)
	Build an OFDM correlator and equalizer.

---

Detailed Description

take a vector of complex constellation points in from an FFT and performs a correlation and equalization.

This block takes the output of an FFT of a received OFDM symbol and finds the start of a frame based on two known symbols. It also looks at the surrounding bins in the FFT output for the correlation in case there is a large frequency shift in the data. This block assumes that the fine frequency shift has already been corrected and that the samples fall in the middle of one FFT bin.

It then uses one of those known symbols to estimate the channel response over all subcarriers and does a simple 1-tap equalization on all subcarriers. This corrects for the phase and amplitude distortion caused by the channel.

---

Constructor & Destructor Documentation

digital_ofdm_frame_acquisition::digital_ofdm_frame_acquisition	(	unsigned int	occupied_carriers,
		unsigned int	fft_length,
		unsigned int	cplen,
		const std::vector< gr_complex > &	known_symbol,
		unsigned int	max_fft_shift_len
	)		[protected]

digital_ofdm_frame_acquisition::~digital_ofdm_frame_acquisition

(

void

)

---

Member Function Documentation

int digital_ofdm_frame_acquisition::general_work	(	int	noutput_items,
		gr_vector_int &	ninput_items,
		gr_vector_const_void_star &	input_items,
		gr_vector_void_star &	output_items
	)		[virtual]

compute output items from input items

Parameters:

noutput_items	number of output items to write on each output stream
ninput_items	number of input items available on each input stream
input_items	vector of pointers to the input items, one entry per input stream
output_items	vector of pointers to the output items, one entry per output stream

Returns:

number of items actually written to each output stream, or -1 on EOF. It is OK to return a value less than noutput_items. -1 <= return value <= noutput_items

general_work must call consume or consume_each to indicate how many items were consumed on each input stream.

Reimplemented from gr_block.

float digital_ofdm_frame_acquisition::snr

(

)

[inline]

Return an estimate of the SNR of the channel.

---

Friends And Related Function Documentation

DIGITAL_API digital_ofdm_frame_acquisition_sptr digital_make_ofdm_frame_acquisition	(	unsigned int	occupied_carriers,
		unsigned int	fft_length,
		unsigned int	cplen,
		const std::vector< gr_complex > &	known_symbol,
		unsigned int	max_fft_shift_len
	)		[friend]

Build an OFDM correlator and equalizer.

Parameters:

occupied_carriers	The number of subcarriers with data in the received symbol
fft_length	The size of the FFT vector (occupied_carriers + unused carriers)
cplen	The length of the cycle prefix
known_symbol	A vector of complex numbers representing a known symbol at the start of a frame (usually a BPSK PN sequence)
max_fft_shift_len	Set's the maximum distance you can look between bins for correlation

---

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

• digital_ofdm_frame_acquisition.h