[Commit-gnuradio] r3935 - gnuradio/branches/developers/trondeau/digital-wip/gnuradio-core/src/python/gnuradio/blksimpl

[trondeau]

Author: trondeau
Date: 2006-11-04 14:26:29 -0700 (Sat, 04 Nov 2006)
New Revision: 3935

Modified:
   
gnuradio/branches/developers/trondeau/digital-wip/gnuradio-core/src/python/gnuradio/blksimpl/dqpsk.py
Log:
Changed how Costas loop is handled in QPSK -- slightly overdamping for improved 
performance; might need more tweaking

Modified: 
gnuradio/branches/developers/trondeau/digital-wip/gnuradio-core/src/python/gnuradio/blksimpl/dqpsk.py
===================================================================
--- 
gnuradio/branches/developers/trondeau/digital-wip/gnuradio-core/src/python/gnuradio/blksimpl/dqpsk.py
       2006-11-04 21:25:35 UTC (rev 3934)
+++ 
gnuradio/branches/developers/trondeau/digital-wip/gnuradio-core/src/python/gnuradio/blksimpl/dqpsk.py
       2006-11-04 21:26:29 UTC (rev 3935)
@@ -238,10 +238,10 @@
         self.agc = gr.feedforward_agc_cc(16, 1.0)
        
         # Costas loop (carrier tracking)
-        # FIXME: need to decide how to handle this more generally; do we pull 
it from higher layer?
         costas_order = 4
-        beta = .25 * self._costas_alpha * self._costas_alpha
-        #self.costas_loop = gr.costas_loop_cc(self._costas_alpha, beta, 0.1, 
-0.1, costas_order)
+        # The value of beta is now set to be overdamped; this value can have a 
huge impact on the
+        # performance of QPSK. Set to 0.25 for critically damped or higher for 
underdamped responses.
+        beta = .10 * self._costas_alpha * self._costas_alpha
         self.costas_loop = gr.costas_loop_cc(self._costas_alpha, beta, 0.002, 
-0.002, costas_order)
 
         # RRC data filter