abstract base class for ATSC equalizer More...

#include <gnuradio/atsc/equalizer_impl.h>

Public Member Functions
	atsci_equalizer ()

virtual	~atsci_equalizer ()

virtual std::vector< double >	taps ()

virtual void	reset ()
	reset state (e.g., on channel change) More...

virtual void	filter (const float input_samples, const atsc::syminfo input_tags, float *output_samples, int nsamples)
	produce `nsamples` of output from given inputs and tags More...

virtual int	ntaps () const =0
	how much history the input data stream requires. More...

virtual int	npretaps () const =0
	how many taps are "in the future". More...

Protected Member Functions
virtual void	filter_normal (const float input_samples, float output_samples, int nsamples)=0

virtual void	filter_data_seg_sync (const float input_samples, float output_samples, int nsamples, int offset)=0

virtual void	filter_field_sync (const float input_samples, float output_samples, int nsamples, int offset, int which_field)=0

Detailed Description

abstract base class for ATSC equalizer

Constructor & Destructor Documentation

atsci_equalizer::atsci_equalizer ( )

virtual atsci_equalizer::~atsci_equalizer ( )

virtual

Member Function Documentation

virtual void atsci_equalizer::filter	(	const float *	input_samples,
		const atsc::syminfo *	input_tags,
		float *	output_samples,
		int	nsamples
	)

virtual

produce nsamples of output from given inputs and tags

This is the main entry point. It examines the input_tags and local state and invokes the appropriate virtual function to handle each sub-segment of the input data.

input_samples must have (nsamples + ntaps() - 1) valid entries. input_samples[0] .. input_samples[nsamples - 1 + ntaps() - 1] are referenced to compute the output values.

input_tags must have nsamples valid entries. input_tags[0] .. input_tags[nsamples - 1] are referenced to compute the output values.

virtual void atsci_equalizer::filter_data_seg_sync	(	const float *	input_samples,
		float *	output_samples,
		int	nsamples,
		int	offset
	)

protectedpure virtual

Input range is known to consist of only a data segment sync or a portion of a data segment sync. nsamples will be in [1,4]. offset will be in [0,3]. offset is the offset of the input from the beginning of the data segment sync pattern.

input_samples has (nsamples + ntaps() - 1) valid entries. input_samples[0] .. input_samples[nsamples - 1 + ntaps() - 1] may be referenced to compute the output values.

Implemented in atsci_equalizer_lms, atsci_equalizer_nop, and atsci_equalizer_lms2.

virtual void atsci_equalizer::filter_field_sync	(	const float *	input_samples,
		float *	output_samples,
		int	nsamples,
		int	offset,
		int	which_field
	)

protectedpure virtual

Input range is known to consist of only a field sync segment or a portion of a field sync segment. nsamples will be in [1,832]. offset will be in [0,831]. offset is the offset of the input from the beginning of the data segment sync pattern. We consider the 4 symbols of the immediately preceding data segment sync to be the first symbols of the field sync segment. which_field is in [0,1] and specifies which field (duh).

input_samples has (nsamples + ntaps() - 1) valid entries. input_samples[0] .. input_samples[nsamples - 1 + ntaps() - 1] may be referenced to compute the output values.

Implemented in atsci_equalizer_lms, atsci_equalizer_nop, and atsci_equalizer_lms2.

virtual void atsci_equalizer::filter_normal	(	const float *	input_samples,
		float *	output_samples,
		int	nsamples
	)

protectedpure virtual

Input range is known NOT TO CONTAIN data segment syncs or field syncs. This should be the fast path. In the non decicion directed case, this just runs the input through the filter without adapting it.

input_samples has (nsamples + ntaps() - 1) valid entries. input_samples[0] .. input_samples[nsamples - 1 + ntaps() - 1] may be referenced to compute the output values.

Implemented in atsci_equalizer_lms, atsci_equalizer_nop, and atsci_equalizer_lms2.

virtual int atsci_equalizer::npretaps ( ) const

pure virtual

how many taps are "in the future".

This allows us to handle what the ATSC folks call "pre-ghosts". What it really does is allow the caller to jack with the offset between the tags and the data so that everything magically works out.

npretaps () must return a value between 0 and ntaps() - 1.

If npretaps () returns 0, this means that the equalizer will only handle multipath "in the past." I suspect that a good value would be something like 15% - 20% of ntaps ().

Implemented in atsci_equalizer_nop, atsci_equalizer_lms2, and atsci_equalizer_lms.

virtual int atsci_equalizer::ntaps ( ) const

pure virtual

how much history the input data stream requires.

This must return a value >= 1. Think of this as the number of samples you need to look at to compute a single output sample.

Implemented in atsci_equalizer_nop, atsci_equalizer_lms2, and atsci_equalizer_lms.

virtual void atsci_equalizer::reset ( )

virtual

reset state (e.g., on channel change)

Note, subclasses must invoke the superclass's method too!

Reimplemented in atsci_equalizer_nop, atsci_equalizer_lms2, and atsci_equalizer_lms.

virtual std::vector<double> atsci_equalizer::taps ( )