#!/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"))