# 3.2.4.3.1. LDPC Encoder parameters¶

## 3.2.4.3.1.1. --enc-cw-size, -N¶

Type: integer --enc-cw-size 1024

Set the codeword size $$N$$.

Note

This parameter value is automatically deduced if the $$H$$ parity matrix is given with the --dec-h-path parameter or if the $$G$$ generator matrix is given with the --enc-g-path parameter.

## 3.2.4.3.1.2. --enc-info-bits, -K¶

Type: integer --enc-info-bits 512

Set the number of information bits $$K$$.

Note

This parameter value is automatically deduced if the $$G$$ generator matrix is given with the --enc-g-path parameter.

Note

In some cases, this parameter value can be automatically deduced if the $$H$$ parity matrix is given with the --dec-h-path parameter. For regular matrices, $$K = N - M$$ where $$N$$ and $$M$$ are the $$H$$ parity matrix dimensions. For non-regular matrices, $$K$$ has to be given.

## 3.2.4.3.1.3. --enc-type¶

Type: text LDPC LDPC_H LDPC_DVBS2 LDPC_IRA LDPC_QC AZCW COSET USER AZCW --enc-type AZCW

Select the encoder type.

Description of the allowed values:

Value Description
LDPC Select the generic encoder that encode from a given $$G$$ generator matrix (to use with the --enc-g-path parameter).
LDPC_H Build the $$G$$ generator matrix from the given $$H$$ parity matrix and then encode with the LDPC method (to use with the --dec-h-path parameter).
LDPC_DVBS2 Select the optimized encoding process for the DVB-S2 $$H$$ matrices (to use with the --enc-cw-size, -N and --enc-info-bits, -K parameters).
LDPC_IRA Select the optimized encoding process for the IRA $$H$$ parity matrices (to use with the --dec-h-path parameter).
LDPC_QC Select the optimized encoding process for the QC $$H$$ parity matrices (to use with the --dec-h-path parameter).
AZCW See the common --enc-type parameter.
COSET See the common --enc-type parameter.
USER See the common --enc-type parameter.

Note

The LDPC_DVBS2 encoder type allow the simulation of the DVB-S2 standard but without the BCH code. All matrices described by the standard (Tables 5a/5b page 22-23) are available. You just need to give to the arguments --enc-info-bits, -K and --enc-cw-size, -N the real $$K$$ and $$N$$ LDPC dimensions, respectively.

## 3.2.4.3.1.4. --enc-g-path¶

Type: file read only --enc-g-path example/path/to/the/G_matrix.alist

Give the path to the $$G$$ generator matrix in an AList or QC formated file.

## 3.2.4.3.1.5. --enc-g-method¶

Type: text IDENTITY LU_DEC IDENTITY --enc-g-method IDENTITY

Specify the method used to build the $$G$$ generator matrix from the $$H$$ parity matrix when using the LDPC_H encoder.

Description of the allowed values:

Value Description
IDENTITY Generate an identity on $$H$$ to get the parity part.
LU_DEC Generate a hollow $$G$$ thanks to the LU decomposition with a guarantee to have the systematic identity. Do not work with irregular matrices.

LU_DEC method is faster than IDENTITY.

## 3.2.4.3.1.6. --enc-g-save-path¶

Type: file write only --enc-g-save-path example/path/to/the/generated/G_matrix.alist

Set the file path where the $$G$$ generator matrix will be saved (AList file format). To use with the LDPC_H encoder.

Hint

When running the LDPC_H encoder, the generation of the $$G$$ matrix can take a non-negligible part of the simulation time. With this option the $$G$$ matrix can be saved once for all and used in the standard LDPC decoder after.