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Diffstat (limited to 'gr-digital/python/ofdm_sync_ml.py')
| -rw-r--r-- | gr-digital/python/ofdm_sync_ml.py | 165 |
1 files changed, 165 insertions, 0 deletions
diff --git a/gr-digital/python/ofdm_sync_ml.py b/gr-digital/python/ofdm_sync_ml.py new file mode 100644 index 000000000..7c75d7f1d --- /dev/null +++ b/gr-digital/python/ofdm_sync_ml.py @@ -0,0 +1,165 @@ +#!/usr/bin/env python +# +# Copyright 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 gnuradio import gr + +class ofdm_sync_ml(gr.hier_block2): + def __init__(self, fft_length, cp_length, snr, kstime, logging): + ''' Maximum Likelihood OFDM synchronizer: + J. van de Beek, M. Sandell, and P. O. Borjesson, "ML Estimation + of Time and Frequency Offset in OFDM Systems," IEEE Trans. + Signal Processing, vol. 45, no. 7, pp. 1800-1805, 1997. + ''' + + gr.hier_block2.__init__(self, "ofdm_sync_ml", + gr.io_signature(1, 1, gr.sizeof_gr_complex), # Input signature + gr.io_signature2(2, 2, gr.sizeof_float, gr.sizeof_char)) # Output signature + + self.input = gr.add_const_cc(0) + + SNR = 10.0**(snr/10.0) + rho = SNR / (SNR + 1.0) + symbol_length = fft_length + cp_length + + # ML Sync + + # Energy Detection from ML Sync + + self.connect(self, self.input) + + # Create a delay line + self.delay = gr.delay(gr.sizeof_gr_complex, fft_length) + self.connect(self.input, self.delay) + + # magnitude squared blocks + self.magsqrd1 = gr.complex_to_mag_squared() + self.magsqrd2 = gr.complex_to_mag_squared() + self.adder = gr.add_ff() + + moving_sum_taps = [rho/2 for i in range(cp_length)] + self.moving_sum_filter = gr.fir_filter_fff(1,moving_sum_taps) + + self.connect(self.input,self.magsqrd1) + self.connect(self.delay,self.magsqrd2) + self.connect(self.magsqrd1,(self.adder,0)) + self.connect(self.magsqrd2,(self.adder,1)) + self.connect(self.adder,self.moving_sum_filter) + + + # Correlation from ML Sync + self.conjg = gr.conjugate_cc(); + self.mixer = gr.multiply_cc(); + + movingsum2_taps = [1.0 for i in range(cp_length)] + self.movingsum2 = gr.fir_filter_ccf(1,movingsum2_taps) + + # Correlator data handler + self.c2mag = gr.complex_to_mag() + self.angle = gr.complex_to_arg() + self.connect(self.input,(self.mixer,1)) + self.connect(self.delay,self.conjg,(self.mixer,0)) + self.connect(self.mixer,self.movingsum2,self.c2mag) + self.connect(self.movingsum2,self.angle) + + # ML Sync output arg, need to find maximum point of this + self.diff = gr.sub_ff() + self.connect(self.c2mag,(self.diff,0)) + self.connect(self.moving_sum_filter,(self.diff,1)) + + #ML measurements input to sampler block and detect + self.f2c = gr.float_to_complex() + self.pk_detect = gr.peak_detector_fb(0.2, 0.25, 30, 0.0005) + self.sample_and_hold = gr.sample_and_hold_ff() + + # use the sync loop values to set the sampler and the NCO + # self.diff = theta + # self.angle = epsilon + + self.connect(self.diff, self.pk_detect) + + # The DPLL corrects for timing differences between CP correlations + use_dpll = 0 + if use_dpll: + self.dpll = gr.dpll_bb(float(symbol_length),0.01) + self.connect(self.pk_detect, self.dpll) + self.connect(self.dpll, (self.sample_and_hold,1)) + else: + self.connect(self.pk_detect, (self.sample_and_hold,1)) + + self.connect(self.angle, (self.sample_and_hold,0)) + + ################################ + # correlate against known symbol + # This gives us the same timing signal as the PN sync block only on the preamble + # we don't use the signal generated from the CP correlation because we don't want + # to readjust the timing in the middle of the packet or we ruin the equalizer settings. + kstime = [k.conjugate() for k in kstime] + kstime.reverse() + self.kscorr = gr.fir_filter_ccc(1, kstime) + self.corrmag = gr.complex_to_mag_squared() + self.div = gr.divide_ff() + + # The output signature of the correlation has a few spikes because the rest of the + # system uses the repeated preamble symbol. It needs to work that generically if + # anyone wants to use this against a WiMAX-like signal since it, too, repeats. + # The output theta of the correlator above is multiplied with this correlation to + # identify the proper peak and remove other products in this cross-correlation + self.threshold_factor = 0.1 + self.slice = gr.threshold_ff(self.threshold_factor, self.threshold_factor, 0) + self.f2b = gr.float_to_char() + self.b2f = gr.char_to_float() + self.mul = gr.multiply_ff() + + # Normalize the power of the corr output by the energy. This is not really needed + # and could be removed for performance, but it makes for a cleaner signal. + # if this is removed, the threshold value needs adjustment. + self.connect(self.input, self.kscorr, self.corrmag, (self.div,0)) + self.connect(self.moving_sum_filter, (self.div,1)) + + self.connect(self.div, (self.mul,0)) + self.connect(self.pk_detect, self.b2f, (self.mul,1)) + self.connect(self.mul, self.slice) + + # Set output signals + # Output 0: fine frequency correction value + # Output 1: timing signal + self.connect(self.sample_and_hold, (self,0)) + self.connect(self.slice, self.f2b, (self,1)) + + + if logging: + self.connect(self.moving_sum_filter, gr.file_sink(gr.sizeof_float, "ofdm_sync_ml-energy_f.dat")) + self.connect(self.diff, gr.file_sink(gr.sizeof_float, "ofdm_sync_ml-theta_f.dat")) + self.connect(self.angle, gr.file_sink(gr.sizeof_float, "ofdm_sync_ml-epsilon_f.dat")) + self.connect(self.corrmag, gr.file_sink(gr.sizeof_float, "ofdm_sync_ml-corrmag_f.dat")) + self.connect(self.kscorr, gr.file_sink(gr.sizeof_gr_complex, "ofdm_sync_ml-kscorr_c.dat")) + self.connect(self.div, gr.file_sink(gr.sizeof_float, "ofdm_sync_ml-div_f.dat")) + self.connect(self.mul, gr.file_sink(gr.sizeof_float, "ofdm_sync_ml-mul_f.dat")) + self.connect(self.slice, gr.file_sink(gr.sizeof_float, "ofdm_sync_ml-slice_f.dat")) + self.connect(self.pk_detect, gr.file_sink(gr.sizeof_char, "ofdm_sync_ml-peaks_b.dat")) + if use_dpll: + self.connect(self.dpll, gr.file_sink(gr.sizeof_char, "ofdm_sync_ml-dpll_b.dat")) + + self.connect(self.sample_and_hold, gr.file_sink(gr.sizeof_float, "ofdm_sync_ml-sample_and_hold_f.dat")) + self.connect(self.input, gr.file_sink(gr.sizeof_gr_complex, "ofdm_sync_ml-input_c.dat")) + |