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   1 #!/usr/bin/env python
   2 #
   3 # Copyright 2007 Free Software Foundation, Inc.
   4 #
   5 # This file is part of GNU Radio
   6 #
   7 # GNU Radio is free software; you can redistribute it and/or modify
   8 # it under the terms of the GNU General Public License as published by
   9 # the Free Software Foundation; either version 2, or (at your option)
  10 # any later version.
  11 #
  12 # GNU Radio is distributed in the hope that it will be useful,
  13 # but WITHOUT ANY WARRANTY; without even the implied warranty of
  14 # MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  15 # GNU General Public License for more details.
  16 #
  17 # You should have received a copy of the GNU General Public License
  18 # along with GNU Radio; see the file COPYING.  If not, write to
  19 # the Free Software Foundation, Inc., 51 Franklin Street,
  20 # Boston, MA 02110-1301, USA.
  21 #
  22
  23 import math
  24 from numpy import fft
  25 from gnuradio import gr
  26
  27 class ofdm_sync_pn(gr.hier_block):
  28     def __init__(self, fg, fft_length, cp_length, logging=False):
  29         ''' OFDM synchronization using PN Correlation:
  30         T. M. Schmidl and D. C. Cox, "Robust Frequency and Timing
  31         Synchonization for OFDM," IEEE Trans. Communications, vol. 45,
  32         no. 12, 1997.
  33         '''
  34
  35         self.fg = fg
  36
  37         # FIXME: when converting to hier_block2's, the output signature
  38         # should be the output of the divider (the normalized peaks) and
  39         # the angle value out of the sample and hold block
  40
  41         self.input = gr.add_const_cc(0)
  42
  43         symbol_length = fft_length + cp_length
  44
  45         # PN Sync
  46
  47         # Create a delay line
  48         self.delay = gr.delay(gr.sizeof_gr_complex, fft_length/2)
  49
  50         # Correlation from ML Sync
  51         self.conjg = gr.conjugate_cc();
  52         self.corr = gr.multiply_cc();
  53
  54         # Create a moving sum filter for the corr output
  55         if 1:
  56             moving_sum_taps = [1.0 for i in range(fft_length//2)]
  57             self.moving_sum_filter = gr.fir_filter_ccf(1,moving_sum_taps)
  58         else:
  59             moving_sum_taps = [complex(1.0,0.0) for i in range(fft_length//2)]
  60             self.moving_sum_filter = gr.fft_filter_ccc(1,moving_sum_taps)
  61
  62         # Create a moving sum filter for the input
  63         self.inputmag2 = gr.complex_to_mag_squared()
  64         movingsum2_taps = [1.0 for i in range(fft_length//2)]
  65
  66         if 1:
  67             self.inputmovingsum = gr.fir_filter_fff(1,movingsum2_taps)
  68         else:
  69             self.inputmovingsum = gr.fft_filter_fff(1,movingsum2_taps)
  70
  71         self.square = gr.multiply_ff()
  72         self.normalize = gr.divide_ff()
  73
  74         # Get magnitude (peaks) and angle (phase/freq error)
  75         self.c2mag = gr.complex_to_mag_squared()
  76         self.angle = gr.complex_to_arg()
  77
  78         self.sample_and_hold = gr.sample_and_hold_ff()
  79
  80         # Mix the signal with an NCO controlled by the sync loop
  81         nco_sensitivity = -2.0/fft_length
  82         self.nco = gr.frequency_modulator_fc(nco_sensitivity)
  83         self.sigmix = gr.multiply_cc()
  84
  85         #ML measurements input to sampler block and detect
  86         self.sub1 = gr.add_const_ff(-1)
  87         self.pk_detect = gr.peak_detector_fb(0.2, 0.25, 30, 0.0005)
  88         self.regen = gr.regenerate_bb(symbol_length)
  89
  90         self.sampler = gr.ofdm_sampler(fft_length,symbol_length)
  91
  92         self.fg.connect(self.input, self.delay)
  93         self.fg.connect(self.input, (self.corr,0))
  94         self.fg.connect(self.delay, self.conjg)
  95         self.fg.connect(self.conjg, (self.corr,1))
  96         self.fg.connect(self.corr, self.moving_sum_filter)
  97         self.fg.connect(self.moving_sum_filter, self.c2mag)
  98         self.fg.connect(self.moving_sum_filter, self.angle)
  99         self.fg.connect(self.angle, (self.sample_and_hold,0))
 100         self.fg.connect(self.sample_and_hold, self.nco)
 101
 102         self.fg.connect(self.input, (self.sigmix,0))
 103         self.fg.connect(self.nco, (self.sigmix,1))
 104         self.fg.connect(self.sigmix, (self.sampler,0))
 105
 106         self.fg.connect(self.input, self.inputmag2, self.inputmovingsum)
 107         self.fg.connect(self.inputmovingsum, (self.square,0))
 108         self.fg.connect(self.inputmovingsum, (self.square,1))
 109         self.fg.connect(self.square, (self.normalize,1))
 110         self.fg.connect(self.c2mag, (self.normalize,0))
 111
 112         # Create a moving sum filter for the corr output
 113         matched_filter_taps = [1.0/cp_length for i in range(cp_length)]
 114         self.matched_filter = gr.fir_filter_fff(1,matched_filter_taps)
 115         self.fg.connect(self.normalize, self.matched_filter)
 116
 117         self.fg.connect(self.matched_filter, self.sub1, self.pk_detect)
 118         self.fg.connect(self.pk_detect, self.regen)
 119         self.fg.connect(self.regen, (self.sampler,1))
 120         self.fg.connect(self.pk_detect, (self.sample_and_hold,1))
 121
 122
 123         if logging:
 124             self.fg.connect(self.matched_filter, gr.file_sink(gr.sizeof_float, "ofdm_sync_pn-mf_f.dat"))
 125             self.fg.connect(self.normalize, gr.file_sink(gr.sizeof_float, "ofdm_sync_pn-theta_f.dat"))
 126             self.fg.connect(self.angle, gr.file_sink(gr.sizeof_float, "ofdm_sync_pn-epsilon_f.dat"))
 127             self.fg.connect(self.pk_detect, gr.file_sink(gr.sizeof_char, "ofdm_sync_pn-peaks_b.dat"))
 128             self.fg.connect(self.regen, gr.file_sink(gr.sizeof_char, "ofdm_sync_pn-regen_b.dat"))
 129             self.fg.connect(self.sigmix, gr.file_sink(gr.sizeof_gr_complex, "ofdm_sync_pn-sigmix_c.dat"))
 130             self.fg.connect(self.sampler, gr.file_sink(gr.sizeof_gr_complex*fft_length, "ofdm_sync_pn-sampler_c.dat"))
 131             self.fg.connect(self.sample_and_hold, gr.file_sink(gr.sizeof_float, "ofdm_sync_pn-sample_and_hold_f.dat"))
 132             self.fg.connect(self.nco, gr.file_sink(gr.sizeof_gr_complex, "ofdm_sync_pn-nco_c.dat"))
 133             self.fg.connect(self.input, gr.file_sink(gr.sizeof_gr_complex, "ofdm_sync_pn-input_c.dat"))
 134
 135         gr.hier_block.__init__(self, fg, self.input, self.sampler)