Houston, we have a trunk.

git-svn-id: http://gnuradio.org/svn/gnuradio/trunk@3122 221aa14e-8319-0410-a670-987f0aec2ac5

1 files changed, 173 insertions, 0 deletions

diff --git a/gr-atsc/src/lib/GrAtscBitTimingLoop2.cc b/gr-atsc/src/lib/GrAtscBitTimingLoop2.cc
new file mode 100644
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+++ b/gr-atsc/src/lib/GrAtscBitTimingLoop2.cc
@@ -0,0 +1,173 @@
+/* -*- c++ -*- */
+/*
+ * Copyright 2002 Free Software Foundation, Inc.
+ * 
+ * This file is part of GNU Radio
+ * 
+ * GNU Radio is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2, or (at your option)
+ * any later version.
+ * 
+ * GNU Radio is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ * 
+ * You should have received a copy of the GNU General Public License
+ * along with GNU Radio; see the file COPYING.  If not, write to
+ * the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
+ * Boston, MA 02111-1307, USA.
+ */
+
+#include <GrAtscBitTimingLoop2.h>
+#include <algorithm>
+#include <atsc_consts.h>
+#include <stdio.h>
+#include <assert.h>
+
+
+static const int	DEC = 2;	// nominal decimation factor
+
+static const unsigned	AVG_WINDOW_LEN = 256;
+static const float	TIMING_RATE_CONST = 1e-5;    // FIXME document interaction with AGC
+
+
+GrAtscBitTimingLoop2::GrAtscBitTimingLoop2 ()
+  : VrDecimatingSigProc<float,float> (1, DEC),
+    next_input(0), dc (0.0002), mu (0.0), last_right(0), use_right_p (true)
+{
+  history = 100;  	// spare input samples in case we need them.
+
+#ifdef _BT_DIAG_OUTPUT_
+  fp_loop = fopen ("loop.out", "w");
+  if (fp_loop == 0){
+    perror ("loop.out");
+    exit (1);
+  }
+    
+  fp_ps = fopen ("ps.out", "w");
+  if (fp_ps == 0){
+    perror ("ps.out");
+    exit (1);
+  }
+#endif
+
+}
+
+//
+// We are nominally a 2x decimator, but our actual rate varies slightly
+// depending on the difference between the transmitter and receiver
+// sampling clocks.  Hence, we need to compute our input ranges
+// explictly.
+
+int
+GrAtscBitTimingLoop2::forecast(VrSampleRange output,
+			      VrSampleRange inputs[]) {
+  /* dec:1 ratio with history */
+  for(unsigned int i=0;i<numberInputs;i++) {
+    inputs[i].index=next_input;
+    inputs[i].size=output.size*decimation + history-1;
+  }
+  return 0;
+}  
+
+inline float
+GrAtscBitTimingLoop2::filter_error (float e)
+{
+  return e;	// identity function
+}
+
+int 
+GrAtscBitTimingLoop2::work (VrSampleRange output, void *ao[],
+			   VrSampleRange inputs[], void *ai[])
+{
+  iType	 *in = ((iType **)ai)[0];
+  oType  *out = ((oType **)ao)[0];
+
+  // Force in-order computation of output stream.
+  // This is required because of our slightly variable decimation factor
+  sync (output.index);
+
+  
+  // We are tasked with producing output.size output samples.  
+  // We will consume approximately 2 * output.size input samples.
+
+
+  unsigned int	ii = 0;		// input index
+  unsigned int	k;		// output index
+
+  // We look at a window of 3 samples that we call left (oldest),
+  // middle, right (newest).  Each time through the loop, the previous
+  // right becomes the new left, and the new samples are middle and
+  // right.
+  //
+  // The basic game plan is to drive the average difference between
+  // right and left to zero.  Given that all transitions are
+  // equiprobable (the data is white) and that the composite matched
+  // filter is symmetric (raised cosine) it turns out that in the
+  // average, if we drive that difference to zero, (implying that the
+  // average slope at the middle point is zero), we'll be sampling
+  // middle at the maximum or minimum point in the pulse.
+
+  iType	left;
+  iType middle;
+  iType	right = last_right;
+
+  for (k = 0; k < output.size; k++){
+
+    left = right;
+    
+    iType middle_raw = produce_sample (in, ii);
+    iType middle_dc = dc.filter (middle_raw);
+    middle = middle_raw - middle_dc;
+
+    iType right_raw = produce_sample (in, ii);
+    iType right_dc = dc.filter (right_raw);
+    right = right_raw - right_dc;
+
+    if (use_right_p)	// produce our output
+      out[k] = right;	
+    else
+      out[k] = middle;
+  }
+
+#ifdef _BT_DIAG_OUTPUT_
+  float	iodata[8];
+  iodata[0] = 0;
+  iodata[1] = out[k];
+  iodata[2] = 0;
+  iodata[3] = 0;
+  iodata[4] = 0;
+  iodata[5] = mu;
+  iodata[6] = 0;
+  iodata[7] = 0;	// spare
+  if (fwrite (iodata, sizeof (iodata), 1, fp_loop) != 1){
+    perror ("fwrite: loop");
+    exit (1);
+  }
+#endif
+
+
+  last_right = right;
+  next_input += ii;	// update next_input so forecast can get us what we need
+  return output.size;
+}
+
+/*!
+ * Produce samples equally spaced in time that are referenced
+ * to the transmitter's sample clock, not ours.
+ *
+ * See pp 523-527 of "Digital Communication Receivers", Meyr,
+ * Moeneclaey and Fechtel, Wiley, 1998.
+ */
+
+GrAtscBitTimingLoop2::iType
+GrAtscBitTimingLoop2::produce_sample (const iType *in, unsigned int &index)
+{
+  iType n = intr.interpolate (&in[index], mu);
+
+  index++;
+  return n;
+}
+