2 # Copyright 2008 Free Software Foundation, Inc.
4 # This file is part of GNU Radio
6 # GNU Radio is free software; you can redistribute it and/or modify
7 # it under the terms of the GNU General Public License as published by
8 # the Free Software Foundation; either version 3, or (at your option)
11 # GNU Radio is distributed in the hope that it will be useful,
12 # but WITHOUT ANY WARRANTY; without even the implied warranty of
13 # MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
14 # GNU General Public License for more details.
16 # You should have received a copy of the GNU General Public License
17 # along with GNU Radio; see the file COPYING. If not, write to
18 # the Free Software Foundation, Inc., 51 Franklin Street,
19 # Boston, MA 02110-1301, USA.
22 from gnuradio import gr, eng_notation
25 n2s = eng_notation.num_to_str
27 class receive_path(gr.hier_block2):
29 if_rate, # Incoming sample rate
30 symbol_rate, # Original symbol rate
31 excess_bw, # RRC excess bandwidth, typically 0.35-0.5
32 costas_alpha, # Costas loop 1st order gain, typically 0.01-0.2
33 costas_beta, # Costas loop 2nd order gain, typically alpha^2/4.0
34 costas_max, # Costas loop max frequency offset in radians/sample
35 mm_gain_mu, # M&M loop 1st order gain, typically 0.001-0.2
36 mm_gain_omega, # M&M loop 2nd order gain, typically alpha^2/4.0
37 mm_omega_limit, # M&M loop max timing error
40 gr.hier_block2.__init__(self, "receive_path",
41 gr.io_signature(1, 1, gr.sizeof_gr_complex), # Input signature
42 gr.io_signature(0, 0, 0)) # Output signature
44 self._if_rate = if_rate
45 self._sps = int(self._if_rate/symbol_rate)
46 print "IF sample rate:", n2s(self._if_rate)
47 print "Symbol rate:", n2s(symbol_rate)
48 print "Samples/symbol:", self._sps
49 print "RRC bandwidth:", excess_bw
51 # Create AGC to scale input to unity
52 self._agc = gr.agc_cc(1e-5, 1.0, 1.0, 1.0)
54 # Create RRC with specified excess bandwidth
55 taps = gr.firdes.root_raised_cosine(1.0, # Gain
56 self._sps, # Sampling rate
58 excess_bw, # Roll-off factor
59 11*self._sps) # Number of taps
61 self._rrc = gr.fir_filter_ccf(1, taps)
63 # Create a Costas loop frequency/phase recovery block
65 print "Costas alpha:", costas_alpha
66 print "Costas beta:", costas_beta
67 print "Costas max:", costas_max
69 self._costas = gr.costas_loop_cc(costas_alpha, # PLL first order gain
70 costas_beta, # PLL second order gain
71 costas_max, # Max frequency offset rad/sample
72 -costas_max, # Min frequency offset rad/sample
75 # Create a M&M bit synchronization retiming block
79 print "MM gain mu:", mm_gain_mu
80 print "MM gain omega:", mm_gain_omega
81 print "MM omega limit:", mm_omega_limit
83 self._mm = gr.clock_recovery_mm_cc(mm_omega, # Initial samples/symbol
84 mm_gain_omega, # Second order gain
85 mm_mu, # Initial symbol phase
86 mm_gain_mu, # First order gain
87 mm_omega_limit) # Maximum timing offset
89 # Add an SNR probe on the demodulated constellation
90 self._snr_probe = gr.probe_mpsk_snr_c(10.0/symbol_rate)
91 self.connect(self._mm, self._snr_probe)
93 # Slice the resulting constellation into bits.
94 # Get inphase channel and make decision about 0
95 self._c2r = gr.complex_to_real()
96 self._slicer = gr.binary_slicer_fb()
98 # Descramble BERT sequence. A channel error will create 3 incorrect bits
99 self._descrambler = gr.descrambler_bb(0x8A, 0x7F, 7) # CCSDS 7-bit descrambler
101 # Measure BER by the density of 0s in the stream
102 self._ber = gr.probe_density_b(1.0/symbol_rate)
104 self.connect(self, self._agc, self._rrc, self._costas, self._mm,
105 self._c2r, self._slicer, self._descrambler, self._ber)
107 def frequency_offset(self):
108 return self._costas.freq()*self._if_rate/(2*math.pi)
110 def timing_offset(self):
111 return self._mm.omega()/self._sps-1.0
114 return self._snr_probe.snr()
117 return (1.0-self._ber.density())/3.0