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#!/usr/bin/env python
#
# Copyright 2015 Free Software Foundation, Inc.
#
# GNU Radio is free software; you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation; either version 3, or (at your option)
# any later version.
#
# GNU Radio is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with GNU Radio; see the file COPYING. If not, write to
# the Free Software Foundation, Inc., 51 Franklin Street,
# Boston, MA 02110-1301, USA.
#
'''
[0] Erdal Arikan: 'Channel Polarization: A Method for Constructing Capacity-Achieving Codes for Symmetric Binary-Input Memoryless Channels', 2009
foundational paper for polar codes.
'''
from channel_construction_bec import calculate_bec_channel_capacities
from channel_construction_bec import design_snr_to_bec_eta
from channel_construction_bec import bhattacharyya_bounds
from channel_construction_bsc import tal_vardy_tpm_algorithm
from helper_functions import *
import matplotlib.pyplot as plt
Z_PARAM_FIRST_HEADER_LINE = "Bhattacharyya parameters (Z-parameters) for a polar code"
def get_frozen_bit_indices_from_capacities(chan_caps, nfrozen):
indexes = np.array([], dtype=int)
while indexes.size < nfrozen:
index = np.argmin(chan_caps)
indexes = np.append(indexes, index)
chan_caps[index] = 2.0 # make absolutely sure value is out of range!
return np.sort(indexes)
def get_frozen_bit_indices_from_z_parameters(z_params, nfrozen):
indexes = np.array([], dtype=int)
while indexes.size < nfrozen:
index = np.argmax(z_params)
indexes = np.append(indexes, index)
z_params[index] = 0.0
return np.sort(indexes)
def get_bec_frozen_indices(nblock, kfrozen, eta):
bec_caps = calculate_bec_channel_capacities(eta, nblock)
positions = get_frozen_bit_indices_from_capacities(bec_caps, kfrozen)
return positions
def get_frozen_bit_mask(frozen_indices, block_size):
frozen_mask = np.zeros(block_size, dtype=int)
frozen_mask[frozen_indices] = 1
return frozen_mask
def frozen_bit_positions(block_size, info_size, design_snr=0.0):
if not design_snr > -1.5917:
print('bad value for design_nsr, must be > -1.5917! default=0.0')
design_snr = 0.0
eta = design_snr_to_bec_eta(design_snr)
return get_bec_frozen_indices(block_size, block_size - info_size, eta)
def generate_filename(block_size, design_snr, mu):
filename = "polar_code_z_parameters_N" + str(int(block_size))
filename += "_SNR" + str(float(design_snr)) + "_MU" + str(int(mu)) + ".polar"
return filename
def default_dir():
dir_def = "~/.gnuradio/polar/"
import os
path = os.path.expanduser(dir_def)
try:
os.makedirs(path)
except OSError:
if not os.path.isdir(path):
raise
return path
def save_z_parameters(z_params, block_size, design_snr, mu):
path = default_dir()
filename = generate_filename(block_size, design_snr, mu)
header = Z_PARAM_FIRST_HEADER_LINE + "\n"
header += "Channel construction method: Tal-Vardy algorithm\n"
header += "Parameters:\n"
header += "block_size=" + str(block_size) + "\n"
header += "design_snr=" + str(design_snr) + "\n"
header += "mu=" + str(mu)
np.savetxt(path + filename, z_params, header=header)
def load_z_parameters(block_size, design_snr, mu):
path = default_dir()
filename = generate_filename(block_size, design_snr, mu)
full_file = path + filename
import os
if not os.path.isfile(full_file):
z_params = tal_vardy_tpm_algorithm(block_size, design_snr, mu)
save_z_parameters(z_params, block_size, design_snr, mu)
z_params = np.loadtxt(full_file)
return z_params
def main():
np.set_printoptions(precision=3, linewidth=150)
print 'channel construction Bhattacharyya bounds by Arikan'
n = 10
m = 2 ** n
k = m // 2
design_snr = 0.0
mu = 32
z_params = load_z_parameters(m, design_snr, mu)
z_bounds = bhattacharyya_bounds(design_snr, m)
print(z_params[-10:])
plt.plot(z_params)
plt.plot(z_bounds)
plt.show()
if __name__ == '__main__':
main()
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