#
# GMSK modulation and demodulation.
#
#
# Copyright 2005-2007,2012 Free Software Foundation, Inc.
#
# This file is part of GNU Radio
#
# SPDX-License-Identifier: GPL-3.0-or-later
#
#
# See gnuradio-examples/python/digital for examples
from math import pi
from pprint import pprint
import inspect
import numpy
from gnuradio import gr, blocks, analog, filter
from . import modulation_utils
from . import digital_python as digital
# default values (used in __init__ and add_options)
_def_samples_per_symbol = 2
_def_bt = 0.35
_def_verbose = False
_def_log = False
_def_gain_mu = None
_def_mu = 0.5
_def_freq_error = 0.0
_def_omega_relative_limit = 0.005
# FIXME: Figure out how to make GMSK work with pfb_arb_resampler_fff for both
# transmit and receive so we don't require integer samples per symbol.
# /////////////////////////////////////////////////////////////////////////////
# GMSK modulator
# /////////////////////////////////////////////////////////////////////////////
class gmsk_mod(gr.hier_block2):
"""
Hierarchical block for Gaussian Minimum Shift Key (GMSK)
modulation.
The input is a byte stream (unsigned char with packed bits)
and the output is the complex modulated signal at baseband.
Args:
samples_per_symbol: samples per baud >= 2 (integer)
bt: Gaussian filter bandwidth * symbol time (float)
verbose: Print information about modulator? (boolean)
log: Print modulation data to files? (boolean)
"""
def __init__(self,
samples_per_symbol=_def_samples_per_symbol,
bt=_def_bt,
verbose=_def_verbose,
log=_def_log):
gr.hier_block2.__init__(self, "gmsk_mod",
gr.io_signature(1, 1, gr.sizeof_char), # Input signature
gr.io_signature(1, 1, gr.sizeof_gr_complex)) # Output signature
samples_per_symbol = int(samples_per_symbol)
self._samples_per_symbol = samples_per_symbol
self._bt = bt
self._differential = False
if not isinstance(samples_per_symbol, int) or samples_per_symbol < 2:
raise TypeError("samples_per_symbol must be an integer >= 2, is %r" % (samples_per_symbol,))
ntaps = 4 * samples_per_symbol # up to 3 bits in filter at once
sensitivity = (pi / 2) / samples_per_symbol # phase change per bit = pi / 2
# Turn it into NRZ data.
#self.nrz = digital.bytes_to_syms()
self.unpack = blocks.packed_to_unpacked_bb(1, gr.GR_MSB_FIRST)
self.nrz = digital.chunks_to_symbols_bf([-1, 1], 1)
# Form Gaussian filter
# Generate Gaussian response (Needs to be convolved with window below).
self.gaussian_taps = filter.firdes.gaussian(
1, # gain
samples_per_symbol, # symbol_rate
bt, # bandwidth * symbol time
ntaps # number of taps
)
self.sqwave = (1,) * samples_per_symbol # rectangular window
self.taps = numpy.convolve(numpy.array(self.gaussian_taps),numpy.array(self.sqwave))
self.gaussian_filter = filter.interp_fir_filter_fff(samples_per_symbol, self.taps)
# FM modulation
self.fmmod = analog.frequency_modulator_fc(sensitivity)
if verbose:
self._print_verbage()
if log:
self._setup_logging()
# Connect & Initialize base class
self.connect(self, self.unpack, self.nrz, self.gaussian_filter, self.fmmod, self)
def samples_per_symbol(self):
return self._samples_per_symbol
@staticmethod
def bits_per_symbol(self=None): # staticmethod that's also callable on an instance
return 1
def _print_verbage(self):
print("bits per symbol = %d" % self.bits_per_symbol())
print("Gaussian filter bt = %.2f" % self._bt)
def _setup_logging(self):
print("Modulation logging turned on.")
self.connect(self.nrz,
blocks.file_sink(gr.sizeof_float, "nrz.dat"))
self.connect(self.gaussian_filter,
blocks.file_sink(gr.sizeof_float, "gaussian_filter.dat"))
self.connect(self.fmmod,
blocks.file_sink(gr.sizeof_gr_complex, "fmmod.dat"))
@staticmethod
def add_options(parser):
"""
Adds GMSK modulation-specific options to the standard parser
"""
parser.add_option("", "--bt", type="float", default=_def_bt,
help="set bandwidth-time product [default=%default] (GMSK)")
@staticmethod
def extract_kwargs_from_options(options):
"""
Given command line options, create dictionary suitable for passing to __init__
"""
return modulation_utils.extract_kwargs_from_options(gmsk_mod.__init__,
('self',), options)
# /////////////////////////////////////////////////////////////////////////////
# GMSK demodulator
# /////////////////////////////////////////////////////////////////////////////
class gmsk_demod(gr.hier_block2):
"""
Hierarchical block for Gaussian Minimum Shift Key (GMSK)
demodulation.
The input is the complex modulated signal at baseband.
The output is a stream of bits packed 1 bit per byte (the LSB)
Args:
samples_per_symbol: samples per baud (integer)
gain_mu: controls rate of mu adjustment (float)
mu: fractional delay [0.0, 1.0] (float)
omega_relative_limit: sets max variation in omega (float)
freq_error: bit rate error as a fraction (float)
verbose: Print information about modulator? (boolean)
log: Print modualtion data to files? (boolean)
"""
def __init__(self,
samples_per_symbol=_def_samples_per_symbol,
gain_mu=_def_gain_mu,
mu=_def_mu,
omega_relative_limit=_def_omega_relative_limit,
freq_error=_def_freq_error,
verbose=_def_verbose,
log=_def_log):
gr.hier_block2.__init__(self, "gmsk_demod",
gr.io_signature(1, 1, gr.sizeof_gr_complex), # Input signature
gr.io_signature(1, 1, gr.sizeof_char)) # Output signature
self._samples_per_symbol = samples_per_symbol
self._gain_mu = gain_mu
self._mu = mu
self._omega_relative_limit = omega_relative_limit
self._freq_error = freq_error
self._differential = False
if samples_per_symbol < 2:
raise TypeError("samples_per_symbol >= 2, is %f" % samples_per_symbol)
self._omega = samples_per_symbol*(1+self._freq_error)
if not self._gain_mu:
self._gain_mu = 0.175
self._gain_omega = .25 * self._gain_mu * self._gain_mu # critically damped
# Demodulate FM
sensitivity = (pi / 2) / samples_per_symbol
self.fmdemod = analog.quadrature_demod_cf(1.0 / sensitivity)
# the clock recovery block tracks the symbol clock and resamples as needed.
# the output of the block is a stream of soft symbols (float)
self.clock_recovery = digital.clock_recovery_mm_ff(self._omega, self._gain_omega,
self._mu, self._gain_mu,
self._omega_relative_limit)
# slice the floats at 0, outputting 1 bit (the LSB of the output byte) per sample
self.slicer = digital.binary_slicer_fb()
if verbose:
self._print_verbage()
if log:
self._setup_logging()
# Connect & Initialize base class
self.connect(self, self.fmdemod, self.clock_recovery, self.slicer, self)
def samples_per_symbol(self):
return self._samples_per_symbol
@staticmethod
def bits_per_symbol(self=None): # staticmethod that's also callable on an instance
return 1
def _print_verbage(self):
print("bits per symbol = %d" % self.bits_per_symbol())
print("M&M clock recovery omega = %f" % self._omega)
print("M&M clock recovery gain mu = %f" % self._gain_mu)
print("M&M clock recovery mu = %f" % self._mu)
print("M&M clock recovery omega rel. limit = %f" % self._omega_relative_limit)
print("frequency error = %f" % self._freq_error)
def _setup_logging(self):
print("Demodulation logging turned on.")
self.connect(self.fmdemod,
blocks.file_sink(gr.sizeof_float, "fmdemod.dat"))
self.connect(self.clock_recovery,
blocks.file_sink(gr.sizeof_float, "clock_recovery.dat"))
self.connect(self.slicer,
blocks.file_sink(gr.sizeof_char, "slicer.dat"))
@staticmethod
def add_options(parser):
"""
Adds GMSK demodulation-specific options to the standard parser
"""
parser.add_option("", "--gain-mu", type="float", default=_def_gain_mu,
help="M&M clock recovery gain mu [default=%default] (GMSK/PSK)")
parser.add_option("", "--mu", type="float", default=_def_mu,
help="M&M clock recovery mu [default=%default] (GMSK/PSK)")
parser.add_option("", "--omega-relative-limit", type="float", default=_def_omega_relative_limit,
help="M&M clock recovery omega relative limit [default=%default] (GMSK/PSK)")
parser.add_option("", "--freq-error", type="float", default=_def_freq_error,
help="M&M clock recovery frequency error [default=%default] (GMSK)")
@staticmethod
def extract_kwargs_from_options(options):
"""
Given command line options, create dictionary suitable for passing to __init__
"""
return modulation_utils.extract_kwargs_from_options(gmsk_demod.__init__,
('self',), options)
#
# Add these to the mod/demod registry
#
modulation_utils.add_type_1_mod('gmsk', gmsk_mod)
modulation_utils.add_type_1_demod('gmsk', gmsk_demod)