[Commit-gnuradio] r9568 - in gnuradio/branches/developers/jcorgan/bert: gnuradio-core/src/lib/general gnuradio-examples/python/digital-bert

[jcorgan]

Author: jcorgan
Date: 2008-09-13 17:30:39 -0600 (Sat, 13 Sep 2008)
New Revision: 9568

Added:
   
gnuradio/branches/developers/jcorgan/bert/gnuradio-examples/python/digital-bert/README
Modified:
   
gnuradio/branches/developers/jcorgan/bert/gnuradio-core/src/lib/general/gr_probe_density_b.h
   
gnuradio/branches/developers/jcorgan/bert/gnuradio-examples/python/digital-bert/benchmark_rx.py
   
gnuradio/branches/developers/jcorgan/bert/gnuradio-examples/python/digital-bert/benchmark_tx.py
   
gnuradio/branches/developers/jcorgan/bert/gnuradio-examples/python/digital-bert/receive_path.py
Log:
docs, cleanup, more parameters

Modified: 
gnuradio/branches/developers/jcorgan/bert/gnuradio-core/src/lib/general/gr_probe_density_b.h
===================================================================
--- 
gnuradio/branches/developers/jcorgan/bert/gnuradio-core/src/lib/general/gr_probe_density_b.h
        2008-09-13 21:21:49 UTC (rev 9567)
+++ 
gnuradio/branches/developers/jcorgan/bert/gnuradio-core/src/lib/general/gr_probe_density_b.h
        2008-09-13 23:30:39 UTC (rev 9568)
@@ -28,6 +28,18 @@
 
 gr_probe_density_b_sptr gr_make_probe_density_b(double alpha);
 
+/*!
+ * This block maintains a running average of the input stream and
+ * makes it available as an accessor function.  The input stream
+ * is type unsigned char.
+ *
+ * If you send this block a stream of unpacked bytes, it will tell
+ * you what the bit density is.
+ *
+ * \param alpha     Average filter constant
+ *
+ */
+
 class gr_probe_density_b : public gr_sync_block
 {
 private:
@@ -42,8 +54,14 @@
 public:
   ~gr_probe_density_b();
   
+  /*!
+   * \brief Returns the current density value
+   */
   double density() const { return d_density; }
 
+  /*!
+   * \brief Set the average filter constant
+   */
   void set_alpha(double alpha);
 
   int work(int noutput_items,

Added: 
gnuradio/branches/developers/jcorgan/bert/gnuradio-examples/python/digital-bert/README
===================================================================
--- 
gnuradio/branches/developers/jcorgan/bert/gnuradio-examples/python/digital-bert/README
                              (rev 0)
+++ 
gnuradio/branches/developers/jcorgan/bert/gnuradio-examples/python/digital-bert/README
      2008-09-13 23:30:39 UTC (rev 9568)
@@ -0,0 +1,62 @@
+BERT testing example scripts
+
+
+benchmark_tx.py
+
+This sets up a BPSK transmitter that is modulated with a pseudorandom
+sequence of bits.  The PN code is generated by sending an all 1s
+sequence through a 7-bit scrambler. The transmitter performs the BPSK
+modulation, then passes the complex baseband waveform through a
+root-raised-cosine filter and onto the USRP.
+
+The --sps parameter controls how many baseband samples per symbol
+are created and passed through the RRC filter, prior to going to the
+USRP over the USB for interpolation to the final DAC rate.
+
+The baseband bit rate is controlled by -r or --rate.  This value, when
+multiplied by the --sps parameter, must result in valid interpolation
+rate for the USRP.  For example, if the baseband rate is 250k bits/sec,
+and the samples per symbol is 4, then the final rate is 1M samples/sec,
+which results in an interpolation rate of 128.  The valid interpolation
+rates for the USRP are multiples of 4 between 16 and 512.
+
+Finally, the RRC excess bandwidth may be specified by --excess-bw.
+(See ./benchmark_tx.py -h for additional parameters.)
+
+
+benchmark_rx.py
+
+This sets up a BPSK receiver to demodulate the received waveform.  It
+accepts a similar set of parameters as the transmitter, except that one
+specifies the USRP decimation rate desired.  The resulting sample stream
+rate must be an integral number of baseband symbols.  For example, the
+parameters corresponding to the above transmitter would be to use a
+decimation rate of 8 (32 sps), 16 (16 sps), 32 (8 sps), 64, (4 sps), or
+128 (2 sps).  The lower the USRP decimation, the more CPU is required to
+demodulate the signal, so not all valid decimation rates will work.
+
+The baseband signal from the USRP is first passed through an AGC to
+establish an average power of 1.0.  It is then passed through a matched
+filter (another RRC), a Costas phase-locked loop, and an M&M bit timing
+recovery loop.  The resulting constellation has an SNR estimation probe
+attached, and is then sliced into a bit stream.
+
+The recovered bits are then passed through a 7-bit descrambler.  If
+there are no channel errors, the all 1s sequence is recovered. In the 
+event of a channel error, there will be a 0 in the bit stream for each
+feedback tap in the descrambler.  In this case, the CCSDS descrambler is
+using 3 feedback taps.
+
+Finally, the signal is passed into a bit density measurement probe. The
+channel BER is measured by dividing the 0s density by three.  This
+measurement is inaccurate at high BER rates (>10%) as the error 0s
+begin to overlap.
+
+The benchmark script will, once per second, output the mean symbol power,
+the average noise variance, the estimated SNR, and the average BER.
+
+NOTE: The particular SNR estimator used is inaccurate below about 7dB,
+and will report erroneously high values even for random noise.
+
+There are a variety of Costas and M&M loop parameters one can adjust.
+See ./benchmark_rx.py -h for the full set.

Modified: 
gnuradio/branches/developers/jcorgan/bert/gnuradio-examples/python/digital-bert/benchmark_rx.py
===================================================================
--- 
gnuradio/branches/developers/jcorgan/bert/gnuradio-examples/python/digital-bert/benchmark_rx.py
     2008-09-13 21:21:49 UTC (rev 9567)
+++ 
gnuradio/branches/developers/jcorgan/bert/gnuradio-examples/python/digital-bert/benchmark_rx.py
     2008-09-13 23:30:39 UTC (rev 9568)
@@ -64,7 +64,13 @@
         if_rate = self._usrp.adc_rate()/options.decim_rate
         self._receiver = receive_path(if_rate,
                                       options.rate,
-                                      options.excess_bw)
+                                      options.excess_bw,
+                                      options.costas_alpha,
+                                      options.costas_beta,
+                                      options.costas_max,
+                                      options.mm_gain_mu,
+                                      options.mm_gain_omega,
+                                      options.mm_omega_limit)
         
         self.connect(self._usrp, self._receiver)
 
@@ -102,7 +108,7 @@
 def get_options():
     parser = OptionParser(option_class=eng_option)
     parser.add_option("-w", "--which", type="int", default=0,
-                      help="select which USRP (0, 1, ...) default is %default",
+                      help="select which USRP (0, 1, ...) (default is 
%default)",
                       metavar="NUM")
     parser.add_option("-R", "--rx-subdev-spec", type="subdev", default=None,
                       help="select USRP Rx side A or B (default=first one with 
a daughterboard)")
@@ -116,6 +122,19 @@
                       help="Select USRP decimation rate (default=%default)")
     parser.add_option("", "--excess-bw", type="eng_float", default=0.35,
                       help="Select RRC excess bandwidth (default=%default)")
+    parser.add_option("", "--costas-alpha", type="eng_float", default=0.2,
+                      help="set Costas loop 1st order gain, 
(default=%default)")
+    parser.add_option("", "--costas-beta", type="eng_float", default=0.01,
+                      help="set Costas loop 2nd order gain, 
(default=%default)")
+    parser.add_option("", "--costas-max", type="eng_float", default=0.005,
+                      help="set Costas loop max freq (rad/sample) 
(default=%default)")
+    parser.add_option("", "--mm-gain-mu", type="eng_float", default=0.2,
+                      help="set M&M loop 1st order gain, (default=%default)")
+    parser.add_option("", "--mm-gain-omega", type="eng_float", default=0.01,
+                      help="set M&M loop 2nd order gain, (default=%default)")
+    parser.add_option("", "--mm-omega-limit", type="eng_float", default=0.005,
+                      help="set M&M max timing error, (default=%default)")
+
                      
     (options, args) = parser.parse_args()
     if len(args) != 0:
@@ -134,8 +153,8 @@
 
     tb = rx_bpsk_block(options)
 
-    print "\nSNR estimator is inaccurate below about 7dB"
-
+    print "\n*** SNR estimator is inaccurate below about 7dB"
+    print "*** BER estimator is inaccurate above about 10%\n"
     updater = status_thread(tb)
 
     try:

Modified: 
gnuradio/branches/developers/jcorgan/bert/gnuradio-examples/python/digital-bert/benchmark_tx.py
===================================================================
--- 
gnuradio/branches/developers/jcorgan/bert/gnuradio-examples/python/digital-bert/benchmark_tx.py
     2008-09-13 21:21:49 UTC (rev 9567)
+++ 
gnuradio/branches/developers/jcorgan/bert/gnuradio-examples/python/digital-bert/benchmark_tx.py
     2008-09-13 23:30:39 UTC (rev 9568)
@@ -24,6 +24,7 @@
 from gnuradio.eng_option import eng_option
 from optparse import OptionParser
 from transmit_path import transmit_path
+import sys
 
 _dac_rate = 128e6
 
@@ -93,6 +94,10 @@
         parser.print_help()
         sys.exit(1)
        
+    if options.freq == None:
+        print "Must supply frequency as -f or --freq"
+        sys.exit(1)
+
     return (options, args)
 
 if __name__ == "__main__":

Modified: 
gnuradio/branches/developers/jcorgan/bert/gnuradio-examples/python/digital-bert/receive_path.py
===================================================================
--- 
gnuradio/branches/developers/jcorgan/bert/gnuradio-examples/python/digital-bert/receive_path.py
     2008-09-13 21:21:49 UTC (rev 9567)
+++ 
gnuradio/branches/developers/jcorgan/bert/gnuradio-examples/python/digital-bert/receive_path.py
     2008-09-13 23:30:39 UTC (rev 9568)
@@ -26,9 +26,15 @@
 
 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
+                 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",
@@ -54,9 +60,6 @@
        self._rrc = gr.fir_filter_ccf(1, taps)
         
         # Create a Costas loop frequency/phase recovery block
-        costas_alpha=0.2
-        costas_beta=costas_alpha*costas_alpha/4.0;
-        costas_max = 0.005
 
         print "Costas alpha:", costas_alpha
         print "Costas beta:", costas_beta
@@ -71,12 +74,8 @@
         # Create a M&M bit synchronization retiming block
         mm_mu = 0.5
         mm_omega = sps
-        mm_gain_mu=0.2
-        mm_gain_omega = mm_gain_mu*mm_gain_mu/0.4
-        mm_omega_limit=0.005
 
         print "MM gain mu:", mm_gain_mu
-        print "MM omega:", mm_omega
         print "MM gain omega:", mm_gain_omega
         print "MM omega limit:", mm_omega_limit
         
@@ -87,7 +86,7 @@
                                            mm_omega_limit) # Maximum timing 
offset
 
         # Add an SNR probe on the demodulated constellation
-        self._snr_probe = gr.probe_mpsk_snr_c(1.0/symbol_rate)
+        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.
@@ -98,8 +97,8 @@
         # Descramble BERT sequence.  A channel error will create 3 incorrect 
bits
         self._descrambler = gr.descrambler_bb(0x8A, 0x7F, 7) # CCSDS 7-bit 
descrambler
 
-        # This will be replaced with the density measurement block
-        self._ber = gr.probe_density_b(1/symbol_rate)
+        # 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)