From 7ad09f5b14eb4c7972029428393ac974ea822f46 Mon Sep 17 00:00:00 2001
From: Johnathan Corgan <johnathan@corganlabs.com>
Date: Sat, 27 Oct 2012 11:28:06 -0700
Subject: [PATCH] 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.

When using --pmf, the threshold may need to be reduced a dB or
two from what would have been optimal without --pmf.

* 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    |  3 ++-
 apps/modes_rx     |  4 +++-
 python/rx_path.py | 18 ++++++++++++++----
 res/modes_rx.ui   | 19 ++++++++++++++++---
 4 files changed, 35 insertions(+), 9 deletions(-)

diff --git a/apps/modes_gui b/apps/modes_gui
index 48368ed..5287579 100755
--- a/apps/modes_gui
+++ b/apps/modes_gui
@@ -242,6 +242,7 @@ 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
@@ -423,7 +424,7 @@ 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)
diff --git a/apps/modes_rx b/apps/modes_rx
index ff582f3..550ffcb 100755
--- a/apps/modes_rx
+++ b/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()
 
diff --git a/python/rx_path.py b/python/rx_path.py
index 09d9a2f..63911de 100644
--- a/python/rx_path.py
+++ b/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)
diff --git a/res/modes_rx.ui b/res/modes_rx.ui
index 3fce593..335b099 100644
--- a/res/modes_rx.ui
+++ b/res/modes_rx.ui
@@ -85,7 +85,7 @@
            </sizepolicy>
           </property>
           <property name="currentIndex">
-           <number>3</number>
+           <number>0</number>
           </property>
           <widget class="QWidget" name="setup">
            <property name="sizePolicy">
@@ -103,7 +103,7 @@
               <x>10</x>
               <y>20</y>
               <width>236</width>
-              <height>193</height>
+              <height>251</height>
              </rect>
             </property>
             <property name="title">
@@ -214,7 +214,7 @@
               </rect>
              </property>
              <property name="currentIndex">
-              <number>1</number>
+              <number>0</number>
              </property>
              <widget class="QWidget" name="page_rf">
               <widget class="QComboBox" name="combo_ant">
@@ -303,6 +303,19 @@
               </widget>
              </widget>
             </widget>
+            <widget class="QCheckBox" name="check_pmf">
+             <property name="geometry">
+              <rect>
+               <x>10</x>
+               <y>200</y>
+               <width>221</width>
+               <height>22</height>
+              </rect>
+             </property>
+             <property name="text">
+              <string>Use Pulse Matched Filtering</string>
+             </property>
+            </widget>
            </widget>
            <widget class="QGroupBox" name="group_output">
             <property name="geometry">