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#
# CPM modulation and demodulation.
#
#
# Copyright 2005-2007,2011 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.
#
# See gnuradio-examples/python/digital for examples
from gnuradio import gr, blks2
from math import pi
import numpy
import digital_swig
import modulation_utils
# default values (used in __init__ and add_options)
_def_samples_per_symbol = 2
_def_bits_per_symbol = 1
_def_h_numerator = 1
_def_h_denominator = 2
_def_cpm_type = 0 # 0=CPFSK, 1=GMSK, 2=RC, 3=GENERAL
_def_bt = 0.35
_def_symbols_per_pulse = 1
_def_generic_taps = numpy.empty(1)
_def_verbose = False
_def_log = False
# /////////////////////////////////////////////////////////////////////////////
# CPM modulator
# /////////////////////////////////////////////////////////////////////////////
class cpm_mod(gr.hier_block2):
def __init__(self,
samples_per_symbol=_def_samples_per_symbol,
bits_per_symbol=_def_bits_per_symbol,
h_numerator=_def_h_numerator,
h_denominator=_def_h_denominator,
cpm_type=_def_cpm_type,
bt=_def_bt,
symbols_per_pulse=_def_symbols_per_pulse,
generic_taps=_def_generic_taps,
verbose=_def_verbose,
log=_def_log):
"""
Hierarchical block for Continuous Phase
modulation.
The input is a byte stream (unsigned char)
representing packed bits and the
output is the complex modulated signal at baseband.
See Proakis for definition of generic CPM signals:
s(t)=exp(j phi(t))
phi(t)= 2 pi h int_0^t f(t') dt'
f(t)=sum_k a_k g(t-kT)
(normalizing assumption: int_0^infty g(t) dt = 1/2)
@param samples_per_symbol: samples per baud >= 2
@type samples_per_symbol: integer
@param bits_per_symbol: bits per symbol
@type bits_per_symbol: integer
@param h_numerator: numerator of modulation index
@type h_numerator: integer
@param h_denominator: denominator of modulation index (numerator and denominator must be relative primes)
@type h_denominator: integer
@param cpm_type: supported types are: 0=CPFSK, 1=GMSK, 2=RC, 3=GENERAL
@type cpm_type: integer
@param bt: bandwidth symbol time product for GMSK
@type bt: float
@param symbols_per_pulse: shaping pulse duration in symbols
@type symbols_per_pulse: integer
@param generic_taps: define a generic CPM pulse shape (sum = samples_per_symbol/2)
@type generic_taps: array of floats
@param verbose: Print information about modulator?
@type verbose: bool
@param debug: Print modulation data to files?
@type debug: bool
"""
gr.hier_block2.__init__(self, "cpm_mod",
gr.io_signature(1, 1, gr.sizeof_char), # Input signature
gr.io_signature(1, 1, gr.sizeof_gr_complex)) # Output signature
self._samples_per_symbol = samples_per_symbol
self._bits_per_symbol = bits_per_symbol
self._h_numerator = h_numerator
self._h_denominator = h_denominator
self._cpm_type = cpm_type
self._bt=bt
if cpm_type == 0 or cpm_type == 2 or cpm_type == 3: # CPFSK, RC, Generic
self._symbols_per_pulse = symbols_per_pulse
elif cpm_type == 1: # GMSK
self._symbols_per_pulse = 4
else:
raise TypeError, ("cpm_type must be an integer in {0,1,2,3}, is %r" % (cpm_type,))
self._generic_taps=numpy.array(generic_taps)
if samples_per_symbol < 2:
raise TypeError, ("samples_per_symbol must be >= 2, is %r" % (samples_per_symbol,))
self.nsymbols = 2**bits_per_symbol
self.sym_alphabet = numpy.arange(-(self.nsymbols-1),self.nsymbols,2).tolist()
self.ntaps = int(self._symbols_per_pulse * samples_per_symbol)
sensitivity = 2 * pi * h_numerator / h_denominator / samples_per_symbol
# Unpack Bytes into bits_per_symbol groups
self.B2s = gr.packed_to_unpacked_bb(bits_per_symbol,gr.GR_MSB_FIRST)
# Turn it into symmetric PAM data.
self.pam = gr.chunks_to_symbols_bf(self.sym_alphabet,1)
# Generate pulse (sum of taps = samples_per_symbol/2)
if cpm_type == 0: # CPFSK
self.taps= (1.0/self._symbols_per_pulse/2,) * self.ntaps
elif cpm_type == 1: # GMSK
gaussian_taps = gr.firdes.gaussian(
1.0/2, # gain
samples_per_symbol, # symbol_rate
bt, # bandwidth * symbol time
self.ntaps # number of taps
)
sqwave = (1,) * samples_per_symbol # rectangular window
self.taps = numpy.convolve(numpy.array(gaussian_taps),numpy.array(sqwave))
elif cpm_type == 2: # Raised Cosine
# generalize it for arbitrary roll-off factor
self.taps = (1-numpy.cos(2*pi*numpy.arange(0,self.ntaps)/samples_per_symbol/self._symbols_per_pulse))/(2*self._symbols_per_pulse)
elif cpm_type == 3: # Generic CPM
self.taps = generic_taps
else:
raise TypeError, ("cpm_type must be an integer in {0,1,2,3}, is %r" % (cpm_type,))
self.filter = blks2.pfb_arb_resampler_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
self.connect(self, self.B2s, self.pam, self.filter, self.fmmod, self)
def samples_per_symbol(self):
return self._samples_per_symbol
def bits_per_symbol(self):
return self._bits_per_symbol
def h_numerator(self):
return self._h_numerator
def h_denominator(self):
return self._h_denominator
def cpm_type(self):
return self._cpm_type
def bt(self):
return self._bt
def symbols_per_pulse(self):
return self._symbols_per_pulse
def _print_verbage(self):
print "Samples per symbol = %d" % self._samples_per_symbol
print "Bits per symbol = %d" % self._bits_per_symbol
print "h = " , self._h_numerator , " / " , self._h_denominator
print "Symbol alphabet = " , self.sym_alphabet
print "Symbols per pulse = %d" % self._symbols_per_pulse
print "taps = " , self.taps
print "CPM type = %d" % self._cpm_type
if self._cpm_type == 1:
print "Gaussian filter BT = %.2f" % self._bt
def _setup_logging(self):
print "Modulation logging turned on."
self.connect(self.B2s,
gr.file_sink(gr.sizeof_float, "symbols.dat"))
self.connect(self.pam,
gr.file_sink(gr.sizeof_float, "pam.dat"))
self.connect(self.filter,
gr.file_sink(gr.sizeof_float, "filter.dat"))
self.connect(self.fmmod,
gr.file_sink(gr.sizeof_gr_complex, "fmmod.dat"))
def add_options(parser):
"""
Adds CPM 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(cpm_mod.__init__,
('self',), options)
extract_kwargs_from_options=staticmethod(extract_kwargs_from_options)
# /////////////////////////////////////////////////////////////////////////////
# CPM demodulator
# /////////////////////////////////////////////////////////////////////////////
#
# Not yet implemented
#
#
# Add these to the mod/demod registry
#
modulation_utils.add_type_1_mod('cpm', cpm_mod)
#modulation_utils.add_type_1_demod('cpm', cpm_demod)
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