# # 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)