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   1 #
   2 # CPM modulation and demodulation.
   3 #
   4 #
   5 # Copyright 2005,2006,2007 Free Software Foundation, Inc.
   6 #
   7 # This file is part of GNU Radio
   8 #
   9 # GNU Radio is free software; you can redistribute it and/or modify
  10 # it under the terms of the GNU General Public License as published by
  11 # the Free Software Foundation; either version 3, or (at your option)
  12 # any later version.
  13 #
  14 # GNU Radio is distributed in the hope that it will be useful,
  15 # but WITHOUT ANY WARRANTY; without even the implied warranty of
  16 # MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  17 # GNU General Public License for more details.
  18 #
  19 # You should have received a copy of the GNU General Public License
  20 # along with GNU Radio; see the file COPYING.  If not, write to
  21 # the Free Software Foundation, Inc., 51 Franklin Street,
  22 # Boston, MA 02110-1301, USA.
  23 #
  24
  25 # See gnuradio-examples/python/digital for examples
  26
  27 from gnuradio import gr
  28 from gnuradio import modulation_utils
  29 from math import pi
  30 import numpy
  31 from pprint import pprint
  32 import inspect
  33
  34 # default values (used in __init__ and add_options)
  35 _def_samples_per_symbol = 2
  36 _def_bits_per_symbol = 1
  37 _def_h_numerator = 1
  38 _def_h_denominator = 2
  39 _def_cpm_type = 0 # 0=CPFSK, 1=GMSK, 2=RC, 3=GENERAL
  40 _def_bt = 0.35
  41 _def_symbols_per_pulse = 1
  42 _def_generic_taps = numpy.empty(1)
  43 _def_verbose = False
  44 _def_log = False
  45
  46
  47 # /////////////////////////////////////////////////////////////////////////////
  48 #                              CPM modulator
  49 # /////////////////////////////////////////////////////////////////////////////
  50
  51 class cpm_mod(gr.hier_block2):
  52     def __init__(self,
  53                  samples_per_symbol=_def_samples_per_symbol,
  54                  bits_per_symbol=_def_bits_per_symbol,
  55                  h_numerator=_def_h_numerator,
  56                  h_denominator=_def_h_denominator,
  57                  cpm_type=_def_cpm_type,
  58                  bt=_def_bt,
  59                  symbols_per_pulse=_def_symbols_per_pulse,
  60                  generic_taps=_def_generic_taps,
  61                  verbose=_def_verbose,
  62                  log=_def_log):
  63         """
  64         Hierarchical block for Continuous Phase
  65         modulation.
  66
  67         The input is a byte stream (unsigned char)
  68         representing packed bits and the
  69         output is the complex modulated signal at baseband.
  70
  71         See Proakis for definition of generic CPM signals:
  72         s(t)=exp(j phi(t))
  73         phi(t)= 2 pi h int_0^t f(t') dt'
  74         f(t)=sum_k a_k g(t-kT)
  75         (normalizing assumption: int_0^infty g(t) dt = 1/2)
  76
  77         @param samples_per_symbol: samples per baud >= 2
  78         @type samples_per_symbol: integer
  79         @param bits_per_symbol: bits per symbol
  80         @type bits_per_symbol: integer
  81         @param h_numerator: numerator of modulation index
  82         @type h_numerator: integer
  83         @param h_denominator: denominator of modulation index (numerator and denominator must be relative primes)
  84         @type h_denominator: integer
  85         @param cpm_type: supported types are: 0=CPFSK, 1=GMSK, 2=RC, 3=GENERAL
  86         @type cpm_type: integer
  87         @param bt: bandwidth symbol time product for GMSK
  88         @type bt: float
  89         @param symbols_per_pulse: shaping pulse duration in symbols
  90         @type symbols_per_pulse: integer
  91         @param generic_taps: define a generic CPM pulse shape (sum = samples_per_symbol/2)
  92         @type generic_taps: array of floats
  93
  94         @param verbose: Print information about modulator?
  95         @type verbose: bool
  96         @param debug: Print modulation data to files?
  97         @type debug: bool
  98         """
  99
 100         gr.hier_block2.__init__("cpm_mod",
 101                                 gr.io_signature(1, 1, gr.sizeof_char),       # Input signature
 102                                 gr.io_signature(1, 1, gr.sizeof_gr_complex)) #  Output signature
 103
 104         self._samples_per_symbol = samples_per_symbol
 105         self._bits_per_symbol = bits_per_symbol
 106         self._h_numerator = h_numerator
 107         self._h_denominator = h_denominator
 108         self._cpm_type = cpm_type
 109         self._bt=bt
 110         if cpm_type == 0 or cpm_type == 2 or cpm_type == 3: # CPFSK, RC, Generic
 111             self._symbols_per_pulse = symbols_per_pulse
 112         elif cpm_type == 1: # GMSK
 113             self._symbols_per_pulse = 4
 114         else:
 115             raise TypeError, ("cpm_type must be an integer in {0,1,2,3}, is %r" % (cpm_type,))
 116
 117         self._generic_taps=numpy.array(generic_taps)
 118
 119         if not isinstance(samples_per_symbol, int) or samples_per_symbol < 2:
 120             raise TypeError, ("samples_per_symbol must be an integer >= 2, is %r" % (samples_per_symbol,))
 121
 122         self.nsymbols = 2**bits_per_symbol
 123         self.sym_alphabet=numpy.arange(-(self.nsymbols-1),self.nsymbols,2)
 124
 125
 126         self.ntaps = self._symbols_per_pulse * samples_per_symbol
 127         sensitivity = 2 * pi * h_numerator / h_denominator / samples_per_symbol
 128
 129         # Unpack Bytes into bits_per_symbol groups
 130         self.B2s = gr.packed_to_unpacked_bb(bits_per_symbol,gr.GR_MSB_FIRST)
 131
 132
 133         # Turn it into symmetric PAM data.
 134         self.pam = gr.chunks_to_symbols_bf(self.sym_alphabet,1)
 135
 136         # Generate pulse (sum of taps = samples_per_symbol/2)
 137         if cpm_type == 0: # CPFSK
 138             self.taps= (1.0/self._symbols_per_pulse/2,) * self.ntaps
 139         elif cpm_type == 1: # GMSK
 140             gaussian_taps = gr.firdes.gaussian(
 141                 1.0/2,                     # gain
 142                 samples_per_symbol,    # symbol_rate
 143                 bt,                    # bandwidth * symbol time
 144                 self.ntaps                  # number of taps
 145                 )
 146             sqwave = (1,) * samples_per_symbol       # rectangular window
 147             self.taps = numpy.convolve(numpy.array(gaussian_taps),numpy.array(sqwave))
 148         elif cpm_type == 2: # Raised Cosine
 149             # generalize it for arbitrary roll-off factor
 150             self.taps = (1-numpy.cos(2*pi*numpy.arange(0,self.ntaps)/samples_per_symbol/self._symbols_per_pulse))/(2*self._symbols_per_pulse)
 151         elif cpm_type == 3: # Generic CPM
 152             self.taps = generic_taps
 153         else:
 154             raise TypeError, ("cpm_type must be an integer in {0,1,2,3}, is %r" % (cpm_type,))
 155
 156         self.filter = gr.interp_fir_filter_fff(samples_per_symbol, self.taps)
 157
 158         # FM modulation
 159         self.fmmod = gr.frequency_modulator_fc(sensitivity)
 160
 161         if verbose:
 162             self._print_verbage()
 163
 164         if log:
 165             self._setup_logging()
 166
 167         # Connect
 168         self.connect(self, self.B2s, self.pam, self.filter, self.fmmod, self)
 169
 170     #def samples_per_symbol(self):
 171         #return self._samples_per_symbol
 172
 173     #def bits_per_symbol(self):
 174         #return self._bits_per_symbol
 175
 176     #def h_numerator(self):
 177         #return self._h_numerator
 178
 179     #def h_denominator(self):
 180         #return self._h_denominator
 181
 182     #def cpm_type(self):
 183         #return self._cpm_type
 184
 185     #def bt(self):
 186         #return self._bt
 187
 188     #def symbols_per_pulse(self):
 189         #return self._symbols_per_pulse
 190
 191
 192     def _print_verbage(self):
 193         print "Samples per symbol = %d" % self._samples_per_symbol
 194         print "Bits per symbol = %d" % self._bits_per_symbol
 195         print "h = " , self._h_numerator , " / " ,  self._h_denominator
 196         print "Symbol alphabet = " , self.sym_alphabet
 197         print "Symbols per pulse = %d" % self._symbols_per_pulse
 198         print "taps = " , self.taps
 199
 200         print "CPM type = %d" % self._cpm_type
 201         if self._cpm_type == 1:
 202              print "Gaussian filter BT = %.2f" % self._bt
 203
 204
 205     def _setup_logging(self):
 206         print "Modulation logging turned on."
 207         self.connect(self.B2s,
 208                      gr.file_sink(gr.sizeof_float, "symbols.dat"))
 209         self.connect(self.pam,
 210                      gr.file_sink(gr.sizeof_float, "pam.dat"))
 211         self.connect(self.filter,
 212                      gr.file_sink(gr.sizeof_float, "filter.dat"))
 213         self.connect(self.fmmod,
 214                      gr.file_sink(gr.sizeof_gr_complex, "fmmod.dat"))
 215
 216
 217     def add_options(parser):
 218         """
 219         Adds CPM modulation-specific options to the standard parser
 220         """
 221         parser.add_option("", "--bt", type="float", default=_def_bt,
 222                           help="set bandwidth-time product [default=%default] (GMSK)")
 223     add_options=staticmethod(add_options)
 224
 225
 226     def extract_kwargs_from_options(options):
 227         """
 228         Given command line options, create dictionary suitable for passing to __init__
 229         """
 230         return modulation_utils.extract_kwargs_from_options(cpm_mod.__init__,
 231                                                             ('self',), options)
 232     extract_kwargs_from_options=staticmethod(extract_kwargs_from_options)
 233
 234
 235
 236 # /////////////////////////////////////////////////////////////////////////////
 237 #                            CPM demodulator
 238 # /////////////////////////////////////////////////////////////////////////////
 239 #
 240 # Not yet implemented
 241 #
 242
 243
 244
 245 #
 246 # Add these to the mod/demod registry
 247 #
 248 modulation_utils.add_type_1_mod('cpm', cpm_mod)
 249 #modulation_utils.add_type_1_demod('cpm', cpm_demod)