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Diffstat (limited to 'gnuradio-examples/python/digital-bert/receive_path.py')
| -rw-r--r-- | gnuradio-examples/python/digital-bert/receive_path.py | 116 |
1 files changed, 116 insertions, 0 deletions
diff --git a/gnuradio-examples/python/digital-bert/receive_path.py b/gnuradio-examples/python/digital-bert/receive_path.py new file mode 100644 index 000000000..84ff32916 --- /dev/null +++ b/gnuradio-examples/python/digital-bert/receive_path.py @@ -0,0 +1,116 @@ +# +# Copyright 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. +# + +from gnuradio import gr, eng_notation +import math + +n2s = eng_notation.num_to_str + +class receive_path(gr.hier_block2): + def __init__(self, + if_rate, # Incoming sample rate + symbol_rate, # Original symbol rate + excess_bw, # RRC excess bandwidth, typically 0.35-0.5 + costas_alpha, # Costas loop 1st order gain, typically 0.01-0.2 + costas_beta, # Costas loop 2nd order gain, typically alpha^2/4.0 + costas_max, # Costas loop max frequency offset in radians/sample + mm_gain_mu, # M&M loop 1st order gain, typically 0.001-0.2 + mm_gain_omega, # M&M loop 2nd order gain, typically alpha^2/4.0 + mm_omega_limit, # M&M loop max timing error + ): + + gr.hier_block2.__init__(self, "receive_path", + gr.io_signature(1, 1, gr.sizeof_gr_complex), # Input signature + gr.io_signature(0, 0, 0)) # Output signature + + sps = int(if_rate/symbol_rate) + print "IF sample rate:", n2s(if_rate) + print "Symbol rate:", n2s(symbol_rate) + print "Samples/symbol:", sps + print "RRC bandwidth:", excess_bw + + # Create AGC to scale input to unity + self._agc = gr.agc_cc(1e-5, 1.0, 1.0, 1.0) + + # Create RRC with specified excess bandwidth + taps = gr.firdes.root_raised_cosine(1.0, # Gain + sps, # Sampling rate + 1.0, # Symbol rate + excess_bw, # Roll-off factor + 11*sps) # Number of taps + + self._rrc = gr.fir_filter_ccf(1, taps) + + # Create a Costas loop frequency/phase recovery block + + print "Costas alpha:", costas_alpha + print "Costas beta:", costas_beta + print "Costas max:", costas_max + + self._costas = gr.costas_loop_cc(costas_alpha, # PLL first order gain + costas_beta, # PLL second order gain + costas_max, # Max frequency offset rad/sample + -costas_max, # Min frequency offset rad/sample + 2) # BPSK + + # Create a M&M bit synchronization retiming block + mm_mu = 0.5 + mm_omega = sps + + print "MM gain mu:", mm_gain_mu + print "MM gain omega:", mm_gain_omega + print "MM omega limit:", mm_omega_limit + + self._mm = gr.clock_recovery_mm_cc(mm_omega, # Initial samples/symbol + mm_gain_omega, # Second order gain + mm_mu, # Initial symbol phase + mm_gain_mu, # First order gain + mm_omega_limit) # Maximum timing offset + + # Add an SNR probe on the demodulated constellation + self._snr_probe = gr.probe_mpsk_snr_c(10.0/symbol_rate) + self.connect(self._mm, self._snr_probe) + + # Slice the resulting constellation into bits. + # Get inphase channel and make decision about 0 + self._c2r = gr.complex_to_real() + self._slicer = gr.binary_slicer_fb() + + # Descramble BERT sequence. A channel error will create 3 incorrect bits + self._descrambler = gr.descrambler_bb(0x8A, 0x7F, 7) # CCSDS 7-bit descrambler + + # Measure BER by the density of 0s in the stream + self._ber = gr.probe_density_b(1.0/symbol_rate) + + self.connect(self, self._agc, self._rrc, self._costas, self._mm, + self._c2r, self._slicer, self._descrambler, self._ber) + + def snr(self): + return self._snr_probe.snr() + + def signal_mean(self): + return self._snr_probe.signal_mean() + + def noise_variance(self): + return self._snr_probe.noise_variance() + + def ber(self): + return (1.0-self._ber.density())/3.0 |