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#!/usr/bin/env python
#
# Copyright 2015 Free Software Foundation, Inc.
#
# This file is part of GNU Radio
#
# SPDX-License-Identifier: GPL-3.0-or-later
#
#
from .Generate_LDPC_matrix_functions import *
# This is an example of how to generate a parity check matrix for
# use with the LDPC Richardson Urbanke encoder. A significant amount
# of matrix manipulation is required, so this process should be done
# before using the encoder at run-time. This process can take quite
# a while, with more time required for larger matrices.
# Not all attempts to create a parity check matrix will be
# successful. The script will terminate and output error messages
# when the process fails. To increase verbosity, edit the verbose
# variable at the top of Generate_LDPC_matrix_functions.py.
# Because random number generation and
# shuffling methods are used, it is not possible to predict what
# starting conditions will result in success. It requires a bit of
# trial and error.
# ----------------------------------------------------------------- #
# First, generate a regular LDPC parity check matrix. Specify
# the properties desired. For example:
n = 200 # number of columns, corresponds to codeword length
p = 3 # column weight
q = 5 # row weight
parity_check_matrix = LDPC_matrix(n_p_q = [n,p,q])
# Richardson and Urbanke's preprocessing method requires a full rank
# matrix to start. The matrices generated by the
# regular_LDPC_code_contructor function will never be full rank. So,
# use the get_full_rank_H_matrix function.
newH = get_full_rank_H_matrix(parity_check_matrix.H)
# At this point, the matrix is no longer regular. (The row/column
# weights are not the same for all rows/columns.)
# Next, some preprocessing steps need to be performed as described
# Richardson and Urbanke in Modern Coding Theory, Appendix A. This
# can take a while...
[bestH,g] = get_best_matrix(newH,100)
# Print(out some of the resulting properties.)
n = bestH.shape[1]
k = n - bestH.shape[0]
print("Parity check matrix properties:")
print("\tSize :", bestH.shape)
print("\tRank :", linalg.matrix_rank(bestH))
print("\tRate : %.3f" % ((k*1.0) / n))
print("\tn :", n, " (codeword length)")
print("\tk :", k, " (info word length)")
print("\tgap : %i" % g)
# Save the matrix to an alist file for future use:
alist_filename = "n_%04i_k_%04i_gap_%02i.alist" % (n,k,g)
write_alist_file(alist_filename,bestH)
print('\nMatrix saved to alist file:', alist_filename, "\n")
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