#
# GMSK modulation and demodulation.
#
#
# Copyright 2005,2006,2007 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.
#
# See gnuradio-examples/python/digital for examples
from gnuradio import gr
import modulation_utils
import digital_swig as digital
from math import pi
import numpy
from pprint import pprint
import inspect
# 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):
def __init__(self,
samples_per_symbol=_def_samples_per_symbol,
bt=_def_bt,
verbose=_def_verbose,
log=_def_log):
"""
Hierarchical block for Gaussian Minimum Shift Key (GMSK)
modulation.
The input is a byte stream (unsigned char) and the
output is the complex modulated signal at baseband.
@param samples_per_symbol: samples per baud >= 2
@type samples_per_symbol: integer
@param bt: Gaussian filter bandwidth * symbol time
@type bt: float
@param verbose: Print information about modulator?
@type verbose: bool
@param debug: Print modualtion data to files?
@type debug: bool
"""
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 = gr.bytes_to_syms()
# Form Gaussian filter
# Generate Gaussian response (Needs to be convolved with window below).
self.gaussian_taps = gr.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 = gr.interp_fir_filter_fff(samples_per_symbol, self.taps)
# FM modulation
self.fmmod = gr.frequency_modulator_fc(sensitivity)
if verbose:
self._print_verbage()
if log:
self._setup_logging()
# Connect & Initialize base class
self.connect(self, self.nrz, self.gaussian_filter, self.fmmod, self)
def samples_per_symbol(self):
return self._samples_per_symbol
def bits_per_symbol(self=None): # staticmethod that's also callable on an instance
return 1
bits_per_symbol = staticmethod(bits_per_symbol) # make it a static method.
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,
gr.file_sink(gr.sizeof_float, "nrz.dat"))
self.connect(self.gaussian_filter,
gr.file_sink(gr.sizeof_float, "gaussian_filter.dat"))
self.connect(self.fmmod,
gr.file_sink(gr.sizeof_gr_complex, "fmmod.dat"))
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)")
add_options=staticmethod(add_options)
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)
extract_kwargs_from_options=staticmethod(extract_kwargs_from_options)
# /////////////////////////////////////////////////////////////////////////////
# GMSK demodulator
# /////////////////////////////////////////////////////////////////////////////
class gmsk_demod(gr.hier_block2):
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):
"""
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)
@param samples_per_symbol: samples per baud
@type samples_per_symbol: integer
@param verbose: Print information about modulator?
@type verbose: bool
@param log: Print modualtion data to files?
@type log: bool
Clock recovery parameters. These all have reasonble defaults.
@param gain_mu: controls rate of mu adjustment
@type gain_mu: float
@param mu: fractional delay [0.0, 1.0]
@type mu: float
@param omega_relative_limit: sets max variation in omega
@type omega_relative_limit: float, typically 0.000200 (200 ppm)
@param freq_error: bit rate error as a fraction
@param float
"""
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 = gr.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
def bits_per_symbol(self=None): # staticmethod that's also callable on an instance
return 1
bits_per_symbol = staticmethod(bits_per_symbol) # make it a static method.
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,
gr.file_sink(gr.sizeof_float, "fmdemod.dat"))
self.connect(self.clock_recovery,
gr.file_sink(gr.sizeof_float, "clock_recovery.dat"))
self.connect(self.slicer,
gr.file_sink(gr.sizeof_char, "slicer.dat"))
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)")
add_options=staticmethod(add_options)
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)
extract_kwargs_from_options=staticmethod(extract_kwargs_from_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)