From e4c8d59714eff4ef571a43f7952a9af2f3d28a98 Mon Sep 17 00:00:00 2001
From: Tom <trondeau@vt.edu>
Date: Sun, 20 Dec 2009 21:57:40 -0500
Subject: Adding FLL to DBPSK demodulator block. Need OTA testing.
---
.../src/python/gnuradio/blks2impl/dbpsk2.py | 41 +++++++++++++++-------
1 file changed, 28 insertions(+), 13 deletions(-)
(limited to 'gnuradio-core/src/python/gnuradio/blks2impl/dbpsk2.py')
diff --git a/gnuradio-core/src/python/gnuradio/blks2impl/dbpsk2.py b/gnuradio-core/src/python/gnuradio/blks2impl/dbpsk2.py
index cd9a207c87..07e1c945b9 100644
--- a/gnuradio-core/src/python/gnuradio/blks2impl/dbpsk2.py
+++ b/gnuradio-core/src/python/gnuradio/blks2impl/dbpsk2.py
@@ -38,6 +38,7 @@ _def_gray_code = True
_def_verbose = False
_def_log = False
+_def_freq_alpha = 4e-3
_def_costas_alpha = 0.1
_def_timing_alpha = 0.100
_def_timing_beta = 0.010
@@ -182,6 +183,7 @@ class dbpsk2_demod(gr.hier_block2):
def __init__(self,
samples_per_symbol=_def_samples_per_symbol,
excess_bw=_def_excess_bw,
+ freq_alpha=_def_freq_alpha,
costas_alpha=_def_costas_alpha,
timing_alpha=_def_timing_alpha,
timing_max_dev=_def_timing_max_dev,
@@ -199,9 +201,11 @@ class dbpsk2_demod(gr.hier_block2):
@type samples_per_symbol: float
@param excess_bw: Root-raised cosine filter excess bandwidth
@type excess_bw: float
- @param costas_alpha: loop filter gain
+ @param freq_alpha: loop filter gain for frequency recovery
+ @type freq_alpha: float
+ @param costas_alpha: loop filter gain for phase/fine frequency recovery
@type costas_alpha: float
- @param timing_alpha: timing loop alpha gain
+ @param timing_alpha: loop alpha gain for timing recovery
@type timing_alpha: float
@param timing_max: timing loop maximum rate deviations
@type timing_max: float
@@ -223,6 +227,8 @@ class dbpsk2_demod(gr.hier_block2):
self._samples_per_symbol = samples_per_symbol
self._excess_bw = excess_bw
+ self._freq_alpha = freq_alpha
+ self._freq_beta = 0.25*self._freq_alpha**2
self._costas_alpha = costas_alpha
self._timing_alpha = timing_alpha
self._timing_beta = _def_timing_beta
@@ -238,14 +244,12 @@ class dbpsk2_demod(gr.hier_block2):
self.agc = gr.agc2_cc(0.6e-1, 1e-3, 1, 1, 100)
#self.agc = gr.feedforward_agc_cc(16, 1.0)
- self._costas_beta = 0.25 * self._costas_alpha * self._costas_alpha
- # Allow a frequency swing of +/- half of the sample rate
- fmin = -0.5
- fmax = 0.5
-
- self.clock_recov = gr.costas_loop_cc(self._costas_alpha,
- self._costas_beta,
- fmax, fmin, arity)
+
+ # Frequency correction
+ self.freq_recov = gr.fll_band_edge_cc(self._samples_per_symbol, self._excess_bw,
+ 11*self._samples_per_symbol,
+ self._freq_alpha, self._freq_beta)
+
# symbol timing recovery with RRC data filter
nfilts = 32
@@ -255,7 +259,17 @@ class dbpsk2_demod(gr.hier_block2):
self._timing_alpha,
taps, nfilts, nfilts/2, self._timing_max_dev)
self.time_recov.set_beta(self._timing_beta)
-
+
+ # Perform phase / fine frequency correction
+ self._costas_beta = 0.25 * self._costas_alpha * self._costas_alpha
+ # Allow a frequency swing of +/- half of the sample rate
+ fmin = -0.5
+ fmax = 0.5
+
+ self.phase_recov = gr.costas_loop_cc(self._costas_alpha,
+ self._costas_beta,
+ fmax, fmin, arity)
+
# Do differential decoding based on phase change of symbols
self.diffdec = gr.diff_phasor_cc()
@@ -280,8 +294,7 @@ class dbpsk2_demod(gr.hier_block2):
# Connect
self.connect(self, self.agc,
- self.clock_recov,
- self.time_recov,
+ self.freq_recov, self.time_recov, self.phase_recov,
self.diffdec, self.slicer, self.symbol_mapper, self.unpack, self)
if sync_out: self.connect(self.time_recov, (self, 1))
@@ -333,6 +346,8 @@ class dbpsk2_demod(gr.hier_block2):
parser.add_option("", "--no-gray-code", dest="gray_code",
action="store_false", default=_def_gray_code,
help="disable gray coding on modulated bits (PSK)")
+ parser.add_option("", "--freq-alpha", type="float", default=_def_freq_alpha,
+ help="set frequency lock loop alpha gain value [default=%default] (PSK)")
parser.add_option("", "--costas-alpha", type="float", default=None,
help="set Costas loop alpha value [default=%default] (PSK)")
parser.add_option("", "--gain-alpha", type="float", default=_def_timing_alpha,
--
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