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   1 #!/usr/bin/env python
   2 #
   3 # Copyright 2006, 2007, 2008 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 3, 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 from gnuradio.blks2impl.ofdm_sync_ml import ofdm_sync_ml
  27 from gnuradio.blks2impl.ofdm_sync_pn import ofdm_sync_pn
  28 from gnuradio.blks2impl.ofdm_sync_pnac import ofdm_sync_pnac
  29 from gnuradio.blks2impl.ofdm_sync_fixed import ofdm_sync_fixed
  30
  31 class ofdm_receiver(gr.hier_block2):
  32     """
  33     Performs receiver synchronization on OFDM symbols.
  34
  35     The receiver performs channel filtering as well as symbol, frequency, and phase synchronization.
  36     The synchronization routines are available in three flavors: preamble correlator (Schmidl and Cox),
  37     modifid preamble correlator with autocorrelation (not yet working), and cyclic prefix correlator
  38     (Van de Beeks).
  39     """
  40
  41     def __init__(self, fft_length, cp_length, occupied_tones, snr, ks, logging=False):
  42         """
  43         Hierarchical block for receiving OFDM symbols.
  44
  45         The input is the complex modulated signal at baseband.
  46         Synchronized packets are sent back to the demodulator.
  47
  48         @param fft_length: total number of subcarriers
  49         @type  fft_length: int
  50         @param cp_length: length of cyclic prefix as specified in subcarriers (<= fft_length)
  51         @type  cp_length: int
  52         @param occupied_tones: number of subcarriers used for data
  53         @type  occupied_tones: int
  54         @param snr: estimated signal to noise ratio used to guide cyclic prefix synchronizer
  55         @type  snr: float
  56         @param ks: known symbols used as preambles to each packet
  57         @type  ks: list of lists
  58         @param logging: turn file logging on or off
  59         @type  logging: bool
  60         """
  61
  62         gr.hier_block2.__init__(self, "ofdm_receiver",
  63                                 gr.io_signature(1, 1, gr.sizeof_gr_complex), # Input signature
  64                                 gr.io_signature2(2, 2, gr.sizeof_gr_complex*occupied_tones, gr.sizeof_char)) # Output signature
  65
  66         bw = (float(occupied_tones) / float(fft_length)) / 2.0
  67         tb = bw*0.08
  68         chan_coeffs = gr.firdes.low_pass (1.0,                     # gain
  69                                           1.0,                     # sampling rate
  70                                           bw+tb,                   # midpoint of trans. band
  71                                           tb,                      # width of trans. band
  72                                           gr.firdes.WIN_HAMMING)   # filter type
  73         self.chan_filt = gr.fft_filter_ccc(1, chan_coeffs)
  74
  75         win = [1 for i in range(fft_length)]
  76
  77         zeros_on_left = int(math.ceil((fft_length - occupied_tones)/2.0))
  78         ks0 = fft_length*[0,]
  79         ks0[zeros_on_left : zeros_on_left + occupied_tones] = ks[0]
  80
  81         ks0 = fft.ifftshift(ks0)
  82         ks0time = fft.ifft(ks0)
  83         # ADD SCALING FACTOR
  84         ks0time = ks0time.tolist()
  85
  86         SYNC = "pn"
  87         if SYNC == "ml":
  88             nco_sensitivity = -1.0/fft_length                             # correct for fine frequency
  89             self.ofdm_sync = ofdm_sync_ml(fft_length, cp_length, snr, ks0time, logging)
  90         elif SYNC == "pn":
  91             nco_sensitivity = -2.0/fft_length                             # correct for fine frequency
  92             self.ofdm_sync = ofdm_sync_pn(fft_length, cp_length, logging)
  93         elif SYNC == "pnac":
  94             nco_sensitivity = -2.0/fft_length                             # correct for fine frequency
  95             self.ofdm_sync = ofdm_sync_pnac(fft_length, cp_length, ks0time, logging)
  96         elif SYNC == "fixed":                                             # for testing only; do not user over the air
  97             self.chan_filt = gr.multiply_const_cc(1.0)                    # remove filter and filter delay for this
  98             nsymbols = 18                                                 # enter the number of symbols per packet
  99             freq_offset = 0.0                                             # if you use a frequency offset, enter it here
 100             nco_sensitivity = -2.0/fft_length                             # correct for fine frequency
 101             self.ofdm_sync = ofdm_sync_fixed(fft_length, cp_length, nsymbols, freq_offset, logging)
 102
 103         # Set up blocks
 104
 105         self.nco = gr.frequency_modulator_fc(nco_sensitivity)         # generate a signal proportional to frequency error of sync block
 106         self.sigmix = gr.multiply_cc()
 107         self.sampler = gr.ofdm_sampler(fft_length, fft_length+cp_length)
 108         self.fft_demod = gr.fft_vcc(fft_length, True, win, True)
 109         self.ofdm_frame_acq = gr.ofdm_frame_acquisition(occupied_tones, fft_length,
 110                                                         cp_length, ks[0])
 111
 112         self.connect(self, self.chan_filt)                            # filter the input channel
 113         self.connect(self.chan_filt, self.ofdm_sync)                  # into the synchronization alg.
 114         self.connect((self.ofdm_sync,0), self.nco, (self.sigmix,1))   # use sync freq. offset output to derotate input signal
 115         self.connect(self.chan_filt, (self.sigmix,0))                 # signal to be derotated
 116         self.connect(self.sigmix, (self.sampler,0))                   # sample off timing signal detected in sync alg
 117         self.connect((self.ofdm_sync,1), (self.sampler,1))            # timing signal to sample at
 118
 119         self.connect((self.sampler,0), self.fft_demod)                # send derotated sampled signal to FFT
 120         self.connect(self.fft_demod, (self.ofdm_frame_acq,0))         # find frame start and equalize signal
 121         self.connect((self.sampler,1), (self.ofdm_frame_acq,1))       # send timing signal to signal frame start
 122         self.connect((self.ofdm_frame_acq,0), (self,0))               # finished with fine/coarse freq correction,
 123         self.connect((self.ofdm_frame_acq,1), (self,1))               # frame and symbol timing, and equalization
 124
 125         if logging:
 126             self.connect(self.chan_filt, gr.file_sink(gr.sizeof_gr_complex, "ofdm_receiver-chan_filt_c.dat"))
 127             self.connect(self.fft_demod, gr.file_sink(gr.sizeof_gr_complex*fft_length, "ofdm_receiver-fft_out_c.dat"))
 128             self.connect(self.ofdm_frame_acq,
 129                          gr.file_sink(gr.sizeof_gr_complex*occupied_tones, "ofdm_receiver-frame_acq_c.dat"))
 130             self.connect((self.ofdm_frame_acq,1), gr.file_sink(1, "ofdm_receiver-found_corr_b.dat"))
 131             self.connect(self.sampler, gr.file_sink(gr.sizeof_gr_complex*fft_length, "ofdm_receiver-sampler_c.dat"))
 132             self.connect(self.sigmix, gr.file_sink(gr.sizeof_gr_complex, "ofdm_receiver-sigmix_c.dat"))
 133             self.connect(self.nco, gr.file_sink(gr.sizeof_gr_complex, "ofdm_receiver-nco_c.dat"))