Added option for pulse matched filtering

Pulse matched filtering places a boxcar filter upstream of the
averager and preamble detector.  The filter length is equivalent
to the number of samples in one Mode S chip (0.5us).  This
technique enhances operation when using sample rates > 4Msps.

* rx_path.py now takes 'use_pmf', defaults to False

* modes_rx has new CLI option '-p' or '--pmf' to turn on PMF

* modes_gui has new checkbox on Setup tab

apps/modes_gui

@@ -239,6 +239,7 @@ class mainwindow(QtGui.QMainWindow):
             options["gain"] = float(self.ui.line_gain.text())
             options["threshold"] = float(self.ui.line_threshold.text())
             options["filename"] = str(self.ui.line_inputfile.text())
+            options["pmf"] = self.ui.check_pmf.checkState()
 
             self.fg = adsb_rx_block(options, self.queue) #create top RX block
             self.runner = top_block_runner(self.fg) #spawn new thread to do RX
@@ -409,7 +410,7 @@ class adsb_rx_block (gr.top_block):
         else:
             raise NotImplementedError
 
-        self.rx_path = air_modes.rx_path(rate, options["threshold"], queue)
+        self.rx_path = air_modes.rx_path(rate, options["threshold"], queue, options["pmf"])
 
         if use_resampler:
             self.lpfiltcoeffs = gr.firdes.low_pass(1, 5*3.2e6, 1.6e6, 300e3)

apps/modes_rx

@@ -110,7 +110,7 @@ class adsb_rx_block (gr.top_block):
     if options.output_all :
       pass_all = 1
 
-    self.rx_path = air_modes.rx_path(rate, options.threshold, queue)
+    self.rx_path = air_modes.rx_path(rate, options.threshold, queue, options.pmf)
 
     if use_resampler:
         self.lpfiltcoeffs = gr.firdes.low_pass(1, 5*3.2e6, 1.6e6, 300e3)
@@ -163,6 +163,8 @@ if __name__ == '__main__':
                       help="FlightGear server to send aircraft data, in format host:port")
   parser.add_option("-d","--rtlsdr", action="store_true", default=False,
                       help="Use RTLSDR dongle instead of UHD source")
+  parser.add_option("-p","--pmf", action="store_true", default=False,
+                      help="Use pulse matched filtering")
                       
   (options, args) = parser.parse_args()
 

python/rx_path.py

@@ -24,7 +24,7 @@ import air_modes_swig
 
 class rx_path(gr.hier_block2):
 
-    def __init__(self, rate, threshold, queue):
+    def __init__(self, rate, threshold, queue, use_pmf=False):
         gr.hier_block2.__init__(self, "modes_rx_path",
                                 gr.io_signature(1, 1, gr.sizeof_gr_complex),
                                 gr.io_signature(0,0,0))
@@ -32,12 +32,20 @@ class rx_path(gr.hier_block2):
         self._rate = int(rate)
         self._threshold = threshold
         self._queue = queue
+        self._spc = int(rate/2e6)
 
         # Convert incoming I/Q baseband to amplitude
         self._demod = gr.complex_to_mag()
+        self._bb = self._demod
+
+        # Pulse matched filter for 0.5us pulses
+        if use_pmf:
+            self._pmf = gr.moving_average_ff(self._spc, 1.0/self._spc, self._rate)
+            self.connect(self._demod, self._pmf)
+            self._bb = self._pmf
 
         # Establish baseline amplitude (noise, interference)
-        self._avg = gr.moving_average_ff(100, 1.0/100, 400) # FIXME
+        self._avg = gr.moving_average_ff(48*self._spc, 1.0/(48*self._spc), self._rate) # 3 preambles
 
         # Synchronize to Mode-S preamble
         self._sync = air_modes_swig.modes_preamble(self._rate, self._threshold)
@@ -45,6 +53,8 @@ class rx_path(gr.hier_block2):
         # Slice Mode-S bits and send to message queue
         self._slicer = air_modes_swig.modes_slicer(self._rate, self._queue)
 
-        self.connect(self, self._demod, (self._sync, 0))
-        self.connect(self._demod, self._avg, (self._sync, 1))
+        # Wire up the flowgraph
+        self.connect(self, self._demod)
+        self.connect(self._bb, (self._sync, 0))
+        self.connect(self._bb, self._avg, (self._sync, 1))
         self.connect(self._sync, self._slicer)

res/modes_rx.ui

@@ -24,7 +24,7 @@
      </rect>
     </property>
     <property name="currentIndex">
-     <number>1</number>
+     <number>0</number>
     </property>
     <widget class="QWidget" name="tab">
      <attribute name="title">
@@ -147,7 +147,7 @@
         </rect>
        </property>
        <property name="currentIndex">
-        <number>1</number>
+        <number>0</number>
        </property>
        <widget class="QWidget" name="page_rf">
         <widget class="QComboBox" name="combo_ant">
@@ -234,10 +234,6 @@
           <string>Filename</string>
          </property>
         </widget>
-        <zorder>line_inputfile</zorder>
-        <zorder>label_13</zorder>
-        <zorder>combo_rate</zorder>
-        <zorder>label_27</zorder>
        </widget>
       </widget>
      </widget>
@@ -460,6 +456,19 @@
        </property>
       </widget>
      </widget>
+     <widget class="QCheckBox" name="check_pmf">
+      <property name="geometry">
+       <rect>
+        <x>20</x>
+        <y>210</y>
+        <width>221</width>
+        <height>22</height>
+       </rect>
+      </property>
+      <property name="text">
+       <string>Use Pulse Matched Filtering</string>
+      </property>
+     </widget>
     </widget>
     <widget class="QWidget" name="dashboard">
      <attribute name="title">