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#
# Copyright 2005,2006,2011 Free Software Foundation, Inc.
#
# This file is part of GNU Radio
#
# 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.
#
"""
PSK modulation and demodulation.
"""
from math import pi, log
from cmath import exp
import digital_swig
import modulation_utils
from utils import mod_codes, gray_code
from generic_mod_demod import generic_mod, generic_demod
from generic_mod_demod import shared_mod_args, shared_demod_args
# Default number of points in constellation.
_def_constellation_points = 4
# The default encoding (e.g. gray-code, set-partition)
_def_mod_code = mod_codes.GRAY_CODE
# Default use of differential encoding
_def_differential = True
def create_encodings(mod_code, arity, differential):
post_diff_code = None
if mod_code not in mod_codes.codes:
raise ValueError('That modulation code does not exist.')
if mod_code == mod_codes.GRAY_CODE:
if differential:
pre_diff_code = gray_code.gray_code(arity)
post_diff_code = None
else:
pre_diff_code = []
post_diff_code = gray_code.gray_code(arity)
elif mod_code == mod_codes.NO_CODE:
pre_diff_code = []
post_diff_code = None
else:
raise ValueError('That modulation code is not implemented for this constellation.')
return (pre_diff_code, post_diff_code)
# /////////////////////////////////////////////////////////////////////////////
# PSK constellation
# /////////////////////////////////////////////////////////////////////////////
def psk_constellation(m=_def_constellation_points, mod_code=_def_mod_code,
differential=_def_differential):
"""
Creates a PSK constellation object.
"""
k = log(m) / log(2.0)
if (k != int(k)):
raise StandardError('Number of constellation points must be a power of two.')
points = [exp(2*pi*(0+1j)*i/m) for i in range(0,m)]
pre_diff_code, post_diff_code = create_encodings(mod_code, m, differential)
if post_diff_code is not None:
inverse_post_diff_code = mod_codes.invert_code(post_diff_code)
points = [points[x] for x in inverse_post_diff_code]
constellation = digital_swig.constellation_psk(points, pre_diff_code, m)
return constellation
# /////////////////////////////////////////////////////////////////////////////
# PSK modulator
# /////////////////////////////////////////////////////////////////////////////
class psk_mod(generic_mod):
"""
Hierarchical block for RRC-filtered PSK modulation.
The input is a byte stream (unsigned char) and the
output is the complex modulated signal at baseband.
Args:
constellation_points: Number of constellation points (must be a power of two) (integer).
mod_code: Whether to use a gray_code (digital.mod_codes.GRAY_CODE) or not (digital.mod_codes.NO_CODE).
differential: Whether to use differential encoding (boolean).
"""
# See generic_mod for additional arguments
__doc__ += shared_mod_args
def __init__(self, constellation_points=_def_constellation_points,
mod_code=_def_mod_code,
differential=_def_differential,
*args, **kwargs):
constellation = psk_constellation(constellation_points, mod_code, differential)
super(psk_mod, self).__init__(constellation, differential, *args, **kwargs)
# /////////////////////////////////////////////////////////////////////////////
# PSK demodulator
#
# /////////////////////////////////////////////////////////////////////////////
class psk_demod(generic_demod):
"""
Hierarchical block for RRC-filtered PSK modulation.
The input is a byte stream (unsigned char) and the
output is the complex modulated signal at baseband.
Args:
constellation_points: Number of constellation points (must be a power of two) (integer).
mod_code: Whether to use a gray_code (digital.mod_codes.GRAY_CODE) or not (digital.mod_codes.NO_CODE).
differential: Whether to use differential encoding (boolean).
"""
# See generic_mod for additional arguments
__doc__ += shared_mod_args
def __init__(self, constellation_points=_def_constellation_points,
mod_code=_def_mod_code,
differential=_def_differential,
*args, **kwargs):
constellation = psk_constellation(constellation_points, mod_code, differential)
super(psk_demod, self).__init__(constellation, differential, *args, **kwargs)
#
# Add these to the mod/demod registry
#
modulation_utils.add_type_1_mod('psk', psk_mod)
modulation_utils.add_type_1_demod('psk', psk_demod)
modulation_utils.add_type_1_constellation('psk', psk_constellation)
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