comnum.CcsdsLdpc#

class comnum.CcsdsLdpc(rate, k=None, *, rule=Ellipsis, alpha=Ellipsis, max_iterations=Ellipsis, layered=Ellipsis)#

An LDPC code of CCSDS 131.0-B-5, Sec. 7: the (8160, 7136) code of rate 223/255 (Sec. 7.3, CcsdsLdpc("7/8")), or an AR4JA code of k = 1024, 4096 or 16384 bits and rate 1/2, 2/3 or 4/5 (Sec. 7.4, CcsdsLdpc("1/2", 1024)), with the encoder of the standard (the circulants of Table C-1, the matrix C of Sec. 7.4.2), the virtual zeros and the punctured bits, decoded by belief propagation on the full parity-check matrix.

Building the AR4JA code of k = 16384 and rate 1/2 inverts an 8192 × 8192 binary matrix: about a second.

Parameters:

  • rate (str) – "7/8" (the (8160, 7136) code), "1/2", "2/3" or "4/5".

  • k (int | None) – the information bits of an AR4JA code (1024, 4096 or 16384).

  • rule (str) – the check-node rule (as LdpcCode.set_decoder).

  • alpha (float) – the scale or the offset of the min-sum rules.

  • max_iterations (int) – the maximum number of iterations.

  • layered (bool) – the layered schedule (default), or flooding (False).

Raises:

ValueError – for another rate or k.

Examples

The lengths of Table 7-5 and a codeword decoded through a noisy channel:

>>> import comnum, numpy as np
>>> code = comnum.CcsdsLdpc("2/3", 1024)
>>> (code.k, code.n)
(1024, 1536)
>>> b = comnum.bits(1024, comnum.Rng(1))
>>> bool(np.array_equal(code.decode(4.0 - 8.0 * code.encode(b)), b))
True
>>> comnum.CcsdsLdpc("7/8").n
8160
app(llr)#

The a posteriori LLRs of the information bits of one codeword.

Parameters:

llr (array_like) – n LLRs.

Returns:

k LLRs (float64).

Return type:

numpy.ndarray

Raises:

ValueError – unless llr has n values.

decode(llr)#

Decode whole codewords of LLRs.

Parameters:

llr (array_like) – a multiple of n LLRs (positive for a 0).

Returns:

k bits per codeword (uint8).

Return type:

numpy.ndarray

Raises:

ValueError – for an input that is not an array of numbers of the expected shape.

encode(bits)#

Encode whole codewords.

Parameters:

bits (array_like) – a multiple of k bits.

Returns:

n bits per codeword (uint8).

Return type:

numpy.ndarray

Raises:

ValueError – for an input that is not an array of bits of the expected shape.

full_codeword(info)#

The codeword of the full parity-check matrix: the 18 virtual zeros of the rate-7/8 code, the information and every parity bit, the punctured ones included.

Parameters:

info (array_like) – k bits.

Returns:

the bits (uint8), a codeword of ldpc.

Return type:

numpy.ndarray

Raises:

ValueError – unless info has k bits.

k#

Information bits per codeword.

Type:

int

ldpc#

The code of the full parity-check matrix (the virtual and punctured bits included), a copy.

Type:

LdpcCode

n#

Transmitted bits per codeword (Table 7-5; 8160 for the rate-7/8 code).

Type:

int

rate#

The rate, "7/8", "1/2", "2/3" or "4/5".

Type:

str