fec.ldpcenc - Construct LDPC encoder object

Syntax

l = fec.ldpcenc(H) l = fec.ldpcenc codeword = encode(l, msg)

Description

The fec.ldpcenc function creates a low-density parity-check (LDPC) encoder object that you can use with the encode method to encode a signal.

l = fec.ldpcenc(H) constructs an LDPC encoder object l for a binary systematic LDPC code with a parity-check matrix H.

H must be a sparse zero-one matrix. n and n-k are the number of columns and the number of rows, respectively, in H. The last n-k columns in H must be an invertible matrix in GF(2).

l = fec.ldpcenc constructs an LDPC encoder object l with a default parity-check matrix (32400-by-64800). For more information, see dvbs2ldpc.

Properties

The following table describes the properties of an LDPC encoder object. Only ParityCheckMatrix is writable. All other properties are derived from it.

Property	Description
`ParityCheckMatrix`	Parity-check matrix of the LDPC code. Stored as a sparse logical matrix with dimension n -k by n (where n >k > 0) of real numbers. All nonzero elements must be equal to 1. The upper bound limit for the value of n is 2³¹-1
`BlockLength`	Total number of bits in a codeword, n.
`NumInfoBits`	Number of information bits in a codeword, k.
`NumParityBits`	Number of parity bits in a codeword, n-k.
`EncodingAlgorithm`	Method for solving the parity-check equation to compute the parity bits using the information bits. Set to `'Forward Substitution'` if the last n-k columns in `H` are a lower triangular matrix, `'Backward Substitution'` if the last n-k columns in `H` are an upper triangular matrix, and `'Matrix Inverse'` in all other situations.

LDPC Encoding Method

This object has a method encode that is used to encode signals.

codeword = encode(l, msg) encodes msg using the LDPC code specified by the LDPC encoder object l. msg must be a binary 1-by-NumInfoBits vector.

codeword is a binary 1-by-BlockLength vector. The first NumInfoBits bits are the information bits (msg) and the last NumParityBits bits are the parity bits. The modulo-2 matrix product of ParityCheckMatrix and codeword' is a zero vector.

Usage Example

This example demonstrates the use of this object.

% Construct a default LDPC encoder object
l = fec.ldpcenc;

% Generate a random binary message
msg = randint(1,l.NumInfoBits,2);

% Encode the message
codeword = encode(l, msg);

% Verify the parity checks (which should be a zero vector)
paritychecks = mod(l.ParityCheckMatrix * codeword', 2);

Example with a Parity-Check Matrix

This example demonstrates the construction of an LDPC encoder object with a parity-check matrix.

i = [1  3  2  4  1  2  3  3  4];   % row indices of 1s
j = [1  1  2  2  3  4  4  5  6];   % column indices of 1s
H = sparse(i,j,ones(length(i),1)); % parity-check matrix H
l = fec.ldpcenc(H);

References

[1] Gallager, Robert G., Low-Density Parity-Check Codes, Cambridge, MA, MIT Press, 1963.