7ad09f5b14
Pulse matched filtering places a boxcar filter upstream of the averager and preamble detector. The filter length is equivalent to the number of samples in one Mode S chip (0.5us). This technique enhances operation when using sample rates > 4Msps. When using --pmf, the threshold may need to be reduced a dB or two from what would have been optimal without --pmf. * rx_path.py now takes 'use_pmf', defaults to False * modes_rx has new CLI option '-p' or '--pmf' to turn on PMF * modes_gui has new checkbox on Setup tab
61 lines
2.2 KiB
Python
61 lines
2.2 KiB
Python
#
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# Copyright 2012 Corgan Labs
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#
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# This file is part of gr-air-modes
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#
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# gr-air-modes is free software; you can redistribute it and/or modify
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# it under the terms of the GNU General Public License as published by
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# the Free Software Foundation; either version 3, or (at your option)
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# any later version.
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#
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# gr-air-modes is distributed in the hope that it will be useful,
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# but WITHOUT ANY WARRANTY; without even the implied warranty of
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# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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# GNU General Public License for more details.
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#
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# You should have received a copy of the GNU General Public License
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# along with gr-air-modes; see the file COPYING. If not, write to
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# the Free Software Foundation, Inc., 51 Franklin Street,
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# Boston, MA 02110-1301, USA.
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#
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from gnuradio import gr
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import air_modes_swig
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class rx_path(gr.hier_block2):
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def __init__(self, rate, threshold, queue, use_pmf=False):
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gr.hier_block2.__init__(self, "modes_rx_path",
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gr.io_signature(1, 1, gr.sizeof_gr_complex),
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gr.io_signature(0,0,0))
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self._rate = int(rate)
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self._threshold = threshold
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self._queue = queue
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self._spc = int(rate/2e6)
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# Convert incoming I/Q baseband to amplitude
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self._demod = gr.complex_to_mag()
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self._bb = self._demod
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# Pulse matched filter for 0.5us pulses
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if use_pmf:
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self._pmf = gr.moving_average_ff(self._spc, 1.0/self._spc, self._rate)
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self.connect(self._demod, self._pmf)
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self._bb = self._pmf
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# Establish baseline amplitude (noise, interference)
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self._avg = gr.moving_average_ff(48*self._spc, 1.0/(48*self._spc), self._rate) # 3 preambles
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# Synchronize to Mode-S preamble
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self._sync = air_modes_swig.modes_preamble(self._rate, self._threshold)
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# Slice Mode-S bits and send to message queue
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self._slicer = air_modes_swig.modes_slicer(self._rate, self._queue)
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# Wire up the flowgraph
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self.connect(self, self._demod)
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self.connect(self._bb, (self._sync, 0))
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self.connect(self._bb, self._avg, (self._sync, 1))
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self.connect(self._sync, self._slicer)
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