Block LDPC code parity-check matrix. More...

#include <itpp/comm/ldpc.h>

Inheritance diagram for itpp::BLDPC_Parity:

Public Member Functions
	BLDPC_Parity ()
	Default constructor.

	BLDPC_Parity (const imat &base_matrix, int exp_factor)
	Construct BLDPC matrix from base matrix.

	BLDPC_Parity (const std::string &filename, int exp_factor)
	Construct BLDPC matrix parsing base matrix from a text file.

void	expand_base (const imat &base_matrix, int exp_factor)
	Create BLDPC matrix from base matrix by expansion.

int	get_exp_factor () const
	Get expansion factor.

imat	get_base_matrix () const
	Get base matrix.

bool	is_valid () const
	Verify initialisation.

void	set_exp_factor (int exp_factor)
	Set expansion factor.

void	load_base_matrix (const std::string &filename)
	Load base matrix from a text file.

void	save_base_matrix (const std::string &filename) const
	Save base matrix to a text file.

void	initialize (int ncheck, int nvar)
	Initialize an empty matrix of size ncheck x nvar.

GF2mat_sparse	get_H (bool transpose=false) const
	Get the parity check matrix, optionally its transposed form.

Sparse_Vec< bin >	get_col (int c) const
	Get a specific column from the matrix.

Sparse_Vec< bin >	get_row (int r) const
	Get a specific row from the matrix.

int	get_nvar () const
	Get the number of variable nodes (number of columns)

int	get_ncheck () const
	Get the number of check nodes (number of rows)

void	set (int i, int j, bin value)
	Set element (i,j) of the parity check matrix to value.

bin	get (int i, int j) const
	Get element (i,j) of the parity check matrix.

bin	operator() (int i, int j) const
	Get element (i,j) of the parity check matrix.

virtual void	display_stats () const
	Display some information about the matrix.

double	get_rate () const
	Get the code rate.

void	import_alist (const GF2mat_sparse_alist &H_alist)
	Import matrix from `GF2mat_sparse_alist` format.

GF2mat_sparse_alist	export_alist () const
	Export matrix to `GF2mat_sparse_alist` format.

void	load_alist (const std::string &alist_file)
	Load matrix from `alist_file` text file in alist format.

void	save_alist (const std::string &alist_file) const
	Save matrix to `alist_file` text file in alist format.

Protected Member Functions
int	check_for_cycles (int L) const
	Check for cycles of length L.

int	check_connectivity (int from_m, int from_n, int to_m, int to_n, int g, int L) const
	Check for connectivity between nodes.

Protected Attributes
bool	init_flag
	Flag that indicates proper initialization.

GF2mat_sparse	H
	The parity check matrix.

GF2mat_sparse	Ht
	The transposed parity check matrix.

int	nvar
	Number of variable nodes.

int	ncheck
	Number of check nodes.

ivec	sumX1
	Actual number of ones in each column.

ivec	sumX2
	Actual number of ones in each row.

Static Protected Attributes
static const int	Nmax = 200
	Maximum node degree class can handle.

Detailed Description

Block LDPC code parity-check matrix.

Author: Adam Piatyszek

Block LDPC Codes (B-LDPC) are a special class of Quasi-Cyclic LDPC Codes (QC-LDPC). Linear encoding properties and memory efficiency are their main advantages.

B-LDPC codes' parity-check matrix is constructed from so-called base matrix by expansion of each single value with a zero matrix or cyclic-shifted identity matrix of size Z x Z, where Z is an expansion factor. Each non negative value of the base matrix represents the cyclic shift value, e.g. 0 means that the identity matrix should not be shifted; 6 means than the identity matrix should be circularly right-shifted by (6 mod Z). Negative values (usually -1) represents zero matrix of size Z x Z.

Please refer to [MYK05] for more details.

References:

[MYK05] S. Myung, K. Yang, J. Kim, "Quasi-Cyclic LDPC Codes for Fast Encoding", IEEE Trans. on Inform. Theory, vol. 51, no. 8, August 2005

Definition at line 461 of file ldpc.h.

Member Function Documentation

int itpp::LDPC_Parity::check_for_cycles ( int L ) const

protectedinherited

Check for cycles of length L.

This function implements a recursive routine to find loops. The function is mainly a tool for testing and debugging more sophisticated functions for graph manipulation.

Parameters

L	length of cycles to look for

Returns: The function returns the number of cycles found of length L or shorter. Cycles may be counted multiple times.

Note: This function can be very slow for large matrices. It is mainly intended as a debugging aid.

Definition at line 249 of file ldpc.cpp.

References itpp::LDPC_Parity::check_connectivity(), itpp::LDPC_Parity::get_col(), itpp::Sparse_Vec< T >::get_nz_indices(), itpp::LDPC_Parity::init_flag, it_assert, itpp::length(), and itpp::LDPC_Parity::nvar.

int itpp::LDPC_Parity::check_connectivity	(	int	from_m,
		int	from_n,
		int	to_m,
		int	to_n,
		int	g,
		int	L
	)		const

protectedinherited

Check for connectivity between nodes.

This function examines whether the point (to_m, to_n) in the matrix can be reached from the point (from_m, from_n) using at most L steps. A recursive search is used.

The function can be used to search for cycles in the matrix. To search for a cycle of length L, set from_m=to_m and from_n=to_n, and godir=0.

Parameters

from_m	starting coordinate, row number
to_m	goal coordinate, row number
from_n	starting coordinate, column number
to_n	goal coordinate, row number
g	direction: 1=start going vertically, 2=start going horizontally
L	number of permitted steps

Returns

-1 or -3 : destination unreachable
-2 : meaningless search (started in a "0" point),
-4 : meaningless search
>=0 : destination reached with certain number of steps left

Note: This function can be very slow depending on the nature of the matrix.

Note that smaller cycles may appear as longer cycles when using this method. More specifically, suppose the method is run with a given L and there are cycles in the neighborhood of (from_m,from_n) of length L-2 or less, but which do not contain (from_m,from_n). These shorter cycles may then also be reported as a cycle of length L. For example, if one of the immediate neighbors of (from_m,from_n) is part of a cycle of length 4 this method will report that (from_m,from_n) is part of a cycle of length 6, if run with L=6. However, if it is known that there are no cycles of length L-2 or smaller, and check_connectivity(from_m,from_n,from_m,from_n,0,L) returns a non-negative value, then one will know with certainty that the point (from_m,from_n) is part of a cycle of length L. (This behavior is inherent to the simple recursive search used.)

Definition at line 192 of file ldpc.cpp.

References itpp::LDPC_Parity::get_col(), itpp::Sparse_Vec< T >::get_nz_indices(), itpp::LDPC_Parity::get_row(), itpp::LDPC_Parity::init_flag, it_assert, and itpp::length().

Referenced by itpp::LDPC_Parity::check_for_cycles(), and itpp::LDPC_Parity_Unstructured::generate_random_H().

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

itpp/comm/ldpc.h
itpp/comm/ldpc.cpp

Public Member Functions

Protected Member Functions

Protected Attributes

Static Protected Attributes

Detailed Description

Member Function Documentation