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#!/usr/bin/env python
#
# Copyright 2006, 2007, 2008 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.
#
import math
from numpy import fft
from gnuradio import gr
import digital_swig
from ofdm_sync_pn import ofdm_sync_pn
from ofdm_sync_fixed import ofdm_sync_fixed
from ofdm_sync_pnac import ofdm_sync_pnac
from ofdm_sync_ml import ofdm_sync_ml
class ofdm_receiver(gr.hier_block2):
"""
Performs receiver synchronization on OFDM symbols.
The receiver performs channel filtering as well as symbol, frequency, and phase synchronization.
The synchronization routines are available in three flavors: preamble correlator (Schmidl and Cox),
modifid preamble correlator with autocorrelation (not yet working), and cyclic prefix correlator
(Van de Beeks).
"""
def __init__(self, fft_length, cp_length, occupied_tones, snr, ks, logging=False):
"""
Hierarchical block for receiving OFDM symbols.
The input is the complex modulated signal at baseband.
Synchronized packets are sent back to the demodulator.
@param fft_length: total number of subcarriers
@type fft_length: int
@param cp_length: length of cyclic prefix as specified in subcarriers (<= fft_length)
@type cp_length: int
@param occupied_tones: number of subcarriers used for data
@type occupied_tones: int
@param snr: estimated signal to noise ratio used to guide cyclic prefix synchronizer
@type snr: float
@param ks: known symbols used as preambles to each packet
@type ks: list of lists
@param logging: turn file logging on or off
@type logging: bool
"""
gr.hier_block2.__init__(self, "ofdm_receiver",
gr.io_signature(1, 1, gr.sizeof_gr_complex), # Input signature
gr.io_signature2(2, 2, gr.sizeof_gr_complex*occupied_tones, gr.sizeof_char)) # Output signature
bw = (float(occupied_tones) / float(fft_length)) / 2.0
tb = bw*0.08
chan_coeffs = gr.firdes.low_pass (1.0, # gain
1.0, # sampling rate
bw+tb, # midpoint of trans. band
tb, # width of trans. band
gr.firdes.WIN_HAMMING) # filter type
self.chan_filt = gr.fft_filter_ccc(1, chan_coeffs)
win = [1 for i in range(fft_length)]
zeros_on_left = int(math.ceil((fft_length - occupied_tones)/2.0))
ks0 = fft_length*[0,]
ks0[zeros_on_left : zeros_on_left + occupied_tones] = ks[0]
ks0 = fft.ifftshift(ks0)
ks0time = fft.ifft(ks0)
# ADD SCALING FACTOR
ks0time = ks0time.tolist()
SYNC = "pn"
if SYNC == "ml":
nco_sensitivity = -1.0/fft_length # correct for fine frequency
self.ofdm_sync = ofdm_sync_ml(fft_length,
cp_length,
snr,
ks0time,
logging)
elif SYNC == "pn":
nco_sensitivity = -2.0/fft_length # correct for fine frequency
self.ofdm_sync = ofdm_sync_pn(fft_length,
cp_length,
logging)
elif SYNC == "pnac":
nco_sensitivity = -2.0/fft_length # correct for fine frequency
self.ofdm_sync = ofdm_sync_pnac(fft_length,
cp_length,
ks0time,
logging)
# for testing only; do not user over the air
# remove filter and filter delay for this
elif SYNC == "fixed":
self.chan_filt = gr.multiply_const_cc(1.0)
nsymbols = 18 # enter the number of symbols per packet
freq_offset = 0.0 # if you use a frequency offset, enter it here
nco_sensitivity = -2.0/fft_length # correct for fine frequency
self.ofdm_sync = ofdm_sync_fixed(fft_length,
cp_length,
nsymbols,
freq_offset,
logging)
# Set up blocks
self.nco = gr.frequency_modulator_fc(nco_sensitivity) # generate a signal proportional to frequency error of sync block
self.sigmix = gr.multiply_cc()
self.sampler = digital_swig.ofdm_sampler(fft_length, fft_length+cp_length)
self.fft_demod = gr.fft_vcc(fft_length, True, win, True)
self.ofdm_frame_acq = digital_swig.ofdm_frame_acquisition(occupied_tones,
fft_length,
cp_length, ks[0])
self.connect(self, self.chan_filt) # filter the input channel
self.connect(self.chan_filt, self.ofdm_sync) # into the synchronization alg.
self.connect((self.ofdm_sync,0), self.nco, (self.sigmix,1)) # use sync freq. offset output to derotate input signal
self.connect(self.chan_filt, (self.sigmix,0)) # signal to be derotated
self.connect(self.sigmix, (self.sampler,0)) # sample off timing signal detected in sync alg
self.connect((self.ofdm_sync,1), (self.sampler,1)) # timing signal to sample at
self.connect((self.sampler,0), self.fft_demod) # send derotated sampled signal to FFT
self.connect(self.fft_demod, (self.ofdm_frame_acq,0)) # find frame start and equalize signal
self.connect((self.sampler,1), (self.ofdm_frame_acq,1)) # send timing signal to signal frame start
self.connect((self.ofdm_frame_acq,0), (self,0)) # finished with fine/coarse freq correction,
self.connect((self.ofdm_frame_acq,1), (self,1)) # frame and symbol timing, and equalization
if logging:
self.connect(self.chan_filt, gr.file_sink(gr.sizeof_gr_complex, "ofdm_receiver-chan_filt_c.dat"))
self.connect(self.fft_demod, gr.file_sink(gr.sizeof_gr_complex*fft_length, "ofdm_receiver-fft_out_c.dat"))
self.connect(self.ofdm_frame_acq,
gr.file_sink(gr.sizeof_gr_complex*occupied_tones, "ofdm_receiver-frame_acq_c.dat"))
self.connect((self.ofdm_frame_acq,1), gr.file_sink(1, "ofdm_receiver-found_corr_b.dat"))
self.connect(self.sampler, gr.file_sink(gr.sizeof_gr_complex*fft_length, "ofdm_receiver-sampler_c.dat"))
self.connect(self.sigmix, gr.file_sink(gr.sizeof_gr_complex, "ofdm_receiver-sigmix_c.dat"))
self.connect(self.nco, gr.file_sink(gr.sizeof_gr_complex, "ofdm_receiver-nco_c.dat"))
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