gr::digital::ofdm_equalizer_simpledfe Class Reference

Simple decision feedback equalizer for OFDM. More...

#include <gnuradio/digital/ofdm_equalizer_simpledfe.h>

Public Types
typedef boost::shared_ptr < ofdm_equalizer_simpledfe >	sptr
Public Types inherited from gr::digital::ofdm_equalizer_1d_pilots
typedef boost::shared_ptr < ofdm_equalizer_1d_pilots >	sptr
Public Types inherited from gr::digital::ofdm_equalizer_base
typedef boost::shared_ptr < ofdm_equalizer_base >	sptr

Public Member Functions
	ofdm_equalizer_simpledfe (int fft_len, const gr::digital::constellation_sptr &constellation, const std::vector< std::vector< int > > &occupied_carriers=std::vector< std::vector< int > >(), const std::vector< std::vector< int > > &pilot_carriers=std::vector< std::vector< int > >(), const std::vector< std::vector< gr_complex > > &pilot_symbols=std::vector< std::vector< gr_complex > >(), int symbols_skipped=0, float alpha=0.1, bool input_is_shifted=true)
	~ofdm_equalizer_simpledfe ()
void	equalize (gr_complex *frame, int n_sym, const std::vector< gr_complex > &initial_taps=std::vector< gr_complex >(), const std::vector< tag_t > &tags=std::vector< tag_t >())
	Run the actual equalization. More...
Public Member Functions inherited from gr::digital::ofdm_equalizer_1d_pilots
	ofdm_equalizer_1d_pilots (int fft_len, const std::vector< std::vector< int > > &occupied_carriers, const std::vector< std::vector< int > > &pilot_carriers, const std::vector< std::vector< gr_complex > > &pilot_symbols, int symbols_skipped, bool input_is_shifted)
	~ofdm_equalizer_1d_pilots ()
void	reset ()
	Reset the channel information state knowledge. More...
void	get_channel_state (std::vector< gr_complex > &taps)
	Return the current channel state. More...
Public Member Functions inherited from gr::digital::ofdm_equalizer_base
	ofdm_equalizer_base (int fft_len)
virtual	~ofdm_equalizer_base ()
int	fft_len ()
sptr	base ()

Static Public Member Functions
static sptr	make (int fft_len, const gr::digital::constellation_sptr &constellation, const std::vector< std::vector< int > > &occupied_carriers=std::vector< std::vector< int > >(), const std::vector< std::vector< int > > &pilot_carriers=std::vector< std::vector< int > >(), const std::vector< std::vector< gr_complex > > &pilot_symbols=std::vector< std::vector< gr_complex > >(), int symbols_skipped=0, float alpha=0.1, bool input_is_shifted=true)

Additional Inherited Members
Protected Attributes inherited from gr::digital::ofdm_equalizer_1d_pilots
std::vector< bool >	d_occupied_carriers
	If d_occupied_carriers[k][l] is true, symbol k, carrier l is carrying data. More...
std::vector< std::vector< bool > >	d_pilot_carriers
	If d_pilot_carriers[k][l] is true, symbol k, carrier l is carrying data. More...
std::vector< std::vector < gr_complex > >	d_pilot_symbols
	If d_pilot_carriers[k][l] is true, d_pilot_symbols[k][l] is its tx'd value. More...
int	d_symbols_skipped
	In case the frame doesn't begin with OFDM symbol 0, this is the index of the first symbol. More...
int	d_pilot_carr_set
	The current position in the set of pilot symbols. More...
std::vector< gr_complex >	d_channel_state
	Vector of length d_fft_len saving the current channel state (on the occupied carriers) More...
Protected Attributes inherited from gr::digital::ofdm_equalizer_base
int	d_fft_len

Detailed Description

Simple decision feedback equalizer for OFDM.

Equalizes an OFDM signal symbol by symbol using knowledge of the complex modulations symbols. For every symbol, the following steps are performed:

• On every sub-carrier, decode the modulation symbol
• Use the difference between the decoded symbol and the received symbol to update the channel state on this carrier
• Whenever a pilot symbol is found, it uses the known pilot symbol to update the channel state.

This equalizer makes a lot of assumptions:

• The initial channel state is good enough to decode the first symbol without error (unless the first symbol only consists of pilot tones)
• The channel changes only very slowly, such that the channel state from one symbol is enough to decode the next
• SNR low enough that equalization will always suffice to correctly decode a symbol If these assumptions are not met, the most common error is that the channel state is estimated incorrectly during equalization; after that, all subsequent symbols will be completely wrong.

Note that the equalized symbols are exact points on the constellation. This means soft information of the modulation symbols is lost after the equalization, which is suboptimal for channel codes that use soft decision.

Member Typedef Documentation

typedef boost::shared_ptr<ofdm_equalizer_simpledfe> gr::digital::ofdm_equalizer_simpledfe::sptr

Constructor & Destructor Documentation

gr::digital::ofdm_equalizer_simpledfe::ofdm_equalizer_simpledfe	(	int	fft_len,
		const gr::digital::constellation_sptr &	constellation,
		const std::vector< std::vector< int > > &	occupied_carriers = std::vector< std::vector< int > >(),
		const std::vector< std::vector< int > > &	pilot_carriers = std::vector< std::vector< int > >(),
		const std::vector< std::vector< gr_complex > > &	pilot_symbols = std::vector< std::vector< gr_complex > >(),
		int	symbols_skipped = 0,
		float	alpha = 0.1,
		bool	input_is_shifted = true
	)

gr::digital::ofdm_equalizer_simpledfe::~ofdm_equalizer_simpledfe

(

)

Member Function Documentation

void gr::digital::ofdm_equalizer_simpledfe::equalize ( gr_complex *  frame, int  n_sym, const std::vector< gr_complex > &  initial_taps = std::vector< gr_complex >(), const std::vector< tag_t > &  tags = std::vector< tag_t >()  )

virtual

Run the actual equalization.

Implements gr::digital::ofdm_equalizer_base.

static sptr gr::digital::ofdm_equalizer_simpledfe::make ( int  fft_len, const gr::digital::constellation_sptr &  constellation, const std::vector< std::vector< int > > &  occupied_carriers = std::vector< std::vector< int > >(), const std::vector< std::vector< int > > &  pilot_carriers = std::vector< std::vector< int > >(), const std::vector< std::vector< gr_complex > > &  pilot_symbols = std::vector< std::vector< gr_complex > >(), int  symbols_skipped = 0, float  alpha = 0.1, bool  input_is_shifted = true  )

static

---

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

• ofdm_equalizer_simpledfe.h