filter: adding a DC blocker algorithm.

5 files changed, 289 insertions, 2 deletions

diff --git a/gnuradio-core/src/lib/filter/Makefile.am b/gnuradio-core/src/lib/filter/Makefile.am
index dee13e239..95489156f 100644
--- a/gnuradio-core/src/lib/filter/Makefile.am
+++ b/gnuradio-core/src/lib/filter/Makefile.am
@@ -216,7 +216,8 @@ libfilter_la_common_SOURCES = 		\
 	gr_pfb_interpolator_ccf.cc	\
 	gr_pfb_arb_resampler_ccf.cc	\
 	gr_pfb_clock_sync_ccf.cc	\
-	gr_pfb_clock_sync_fff.cc
+	gr_pfb_clock_sync_fff.cc	\
+	gr_dc_blocker_cc.cc
 
 libfilter_qa_la_common_SOURCES = 	\
 	qa_filter.cc			\
@@ -306,7 +307,8 @@ grinclude_HEADERS = 			\
 	gr_pfb_interpolator_ccf.h	\
 	gr_pfb_arb_resampler_ccf.h	\
 	gr_pfb_clock_sync_ccf.h		\
-	gr_pfb_clock_sync_fff.h
+	gr_pfb_clock_sync_fff.h		\
+	gr_dc_blocker_cc.h
 
 noinst_HEADERS = 			\
 	assembly.h			\
@@ -372,6 +374,7 @@ swiginclude_HEADERS =			\
 	gr_pfb_arb_resampler_ccf.i	\
 	gr_pfb_clock_sync_ccf.i		\
 	gr_pfb_clock_sync_fff.i		\
+	gr_dc_blocker_cc.i		\
 	$(GENERATED_I)
 
 
diff --git a/gnuradio-core/src/lib/filter/filter.i b/gnuradio-core/src/lib/filter/filter.i
index 645607cba..b8f4d06eb 100644
--- a/gnuradio-core/src/lib/filter/filter.i
+++ b/gnuradio-core/src/lib/filter/filter.i
@@ -39,6 +39,7 @@
 #include <gr_pfb_arb_resampler_ccf.h>
 #include <gr_pfb_clock_sync_ccf.h>
 #include <gr_pfb_clock_sync_fff.h>
+#include <gr_dc_blocker_cc.h>
 %}
 
 %include "gr_iir_filter_ffd.i"
@@ -62,5 +63,6 @@
 %include "gr_pfb_arb_resampler_ccf.i"
 %include "gr_pfb_clock_sync_ccf.i"
 %include "gr_pfb_clock_sync_fff.i"
+%include "gr_dc_blocker_cc.i"
 
 %include "filter_generated.i"
diff --git a/gnuradio-core/src/lib/filter/gr_dc_blocker_cc.cc b/gnuradio-core/src/lib/filter/gr_dc_blocker_cc.cc
new file mode 100644
index 000000000..66f59f240
--- /dev/null
+++ b/gnuradio-core/src/lib/filter/gr_dc_blocker_cc.cc
@@ -0,0 +1,138 @@
+/* -*- c++ -*- */
+/*
+ * Copyright 2011 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 3, 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., 51 Franklin Street,
+ * Boston, MA 02110-1301, USA.
+ */
+
+#ifdef HAVE_CONFIG_H
+#include "config.h"
+#endif
+
+#include <gr_dc_blocker_cc.h>
+#include <gr_io_signature.h>
+#include <cstdio>
+
+moving_averager::moving_averager(int D)
+  : d_length(D), d_out(0), d_out_d1(0), d_out_d2(0)
+{
+  d_delay_line = std::deque<gr_complex>(d_length-1, gr_complex(0,0));
+}
+
+moving_averager::~moving_averager()
+{
+}
+
+gr_complex
+moving_averager::filter(gr_complex x)
+{
+  d_out_d1 = d_out;
+  d_delay_line.push_back(x);
+  d_out = d_delay_line[0];
+  d_delay_line.pop_front();
+    
+  gr_complex y = x - d_out_d1 + d_out_d2;
+  d_out_d2 = y;
+    
+  return (y / (float)(d_length)); 
+}
+
+
+
+gr_dc_blocker_cc_sptr gr_make_dc_blocker_cc (int D, bool long_form)
+{
+  return gnuradio::get_initial_sptr(new gr_dc_blocker_cc(D, long_form));
+}
+
+
+gr_dc_blocker_cc::gr_dc_blocker_cc (int D, bool long_form)
+  : gr_sync_block ("dc_blocker_cc",
+		   gr_make_io_signature (1, 1, sizeof(gr_complex)),
+		   gr_make_io_signature (1, 1, sizeof(gr_complex))),
+    d_length(D), d_long_form(long_form)
+{
+  if(d_long_form) {
+    d_ma_0 = new moving_averager(D);
+    d_ma_1 = new moving_averager(D);
+    d_ma_2 = new moving_averager(D);
+    d_ma_3 = new moving_averager(D);
+    d_delay_line = std::deque<gr_complex>(d_length-1, gr_complex(0,0));
+  }
+  else {
+    d_ma_0 = new moving_averager(D);
+    d_ma_1 = new moving_averager(D);
+  }
+}
+
+gr_dc_blocker_cc::~gr_dc_blocker_cc()
+{
+  if(d_long_form) {
+    delete d_ma_0;
+    delete d_ma_1;
+    delete d_ma_2;
+    delete d_ma_3;
+  }
+  else {
+    delete d_ma_0;
+    delete d_ma_1;
+  }
+}
+
+int
+gr_dc_blocker_cc::get_group_delay()
+{
+  if(d_long_form)
+    return (2*d_length-2);
+  else
+    return d_length - 1;
+}
+
+int
+gr_dc_blocker_cc::work(int noutput_items,
+		       gr_vector_const_void_star &input_items,
+		       gr_vector_void_star &output_items)
+{
+  const gr_complex *in = (const gr_complex*)input_items[0];
+  gr_complex *out = (gr_complex*)output_items[0];
+
+  if(d_long_form) {
+    gr_complex y1, y2, y3, y4, d;
+    for(int i = 0; i < noutput_items; i++) {
+      y1 = d_ma_0->filter(in[i]);
+      y2 = d_ma_1->filter(y1);
+      y3 = d_ma_2->filter(y2);
+      y4 = d_ma_3->filter(y3);
+
+      d_delay_line.push_back(d_ma_0->delayed_sig());
+      d = d_delay_line[0];
+      d_delay_line.pop_front();
+
+      out[i] = d - y4;
+    }
+  }
+  else {
+    gr_complex y1, y2;
+    for(int i = 0; i < noutput_items; i++) {
+      y1 = d_ma_0->filter(in[i]);
+      y2 = d_ma_1->filter(y1);
+      out[i] = d_ma_0->delayed_sig() - y2;
+    }
+  }
+
+  return noutput_items;
+}
diff --git a/gnuradio-core/src/lib/filter/gr_dc_blocker_cc.h b/gnuradio-core/src/lib/filter/gr_dc_blocker_cc.h
new file mode 100644
index 000000000..26a2247ea
--- /dev/null
+++ b/gnuradio-core/src/lib/filter/gr_dc_blocker_cc.h
@@ -0,0 +1,110 @@
+/* -*- c++ -*- */
+/*
+ * Copyright 2011 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 3, 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., 51 Franklin Street,
+ * Boston, MA 02110-1301, USA.
+ */
+
+
+#ifndef INCLUDED_GR_DC_BLOCKER_CC_H
+#define	INCLUDED_GR_DC_BLOCKER_CC_H
+
+#include <gr_sync_block.h>
+#include <deque>
+
+class gr_dc_blocker_cc;
+typedef boost::shared_ptr<gr_dc_blocker_cc> gr_dc_blocker_cc_sptr;
+gr_dc_blocker_cc_sptr gr_make_dc_blocker_cc (int D=32, bool long_form=true);
+
+/*!
+ * \class gr_dc_blocker_cc
+ * \brief a computationally efficient controllabel DC blocker
+ *
+ * \ingroup filter_blk
+ * 
+ * This block implements a computationally efficient DC blocker that produces
+ * a tigher notch filter around DC for a smaller group delay than an
+ * equivalent FIR filter or using a single pole IIR filter.
+ *
+ * The block defaults to using a delay line of length 32 and the long form
+ * of the filter. Optionally, the delay line length can be changed to alter
+ * the width of the DC notch (longer lines will decrease the width).
+ *
+ * The long form of the filter produces a nearly flat response outside of
+ * the notch but at the cost of a group delay of 2D-2.
+ *
+ * The short form of the filter does not have a flat a response in the
+ * passband but has a group delay of only D-1 and is cheaper to compute.
+ *
+ * The theory behind this block can be found in the paper:
+ *
+ *    <B><EM>R. Yates, "DC Blocker Algorithms," IEEE Signal Processing Magazine,
+ *        Mar. 2008, pp 132-134.</EM></B>
+ */
+class moving_averager
+{
+public:
+  moving_averager(int D);
+  ~moving_averager();
+
+  gr_complex filter(gr_complex x);
+  gr_complex delayed_sig() { return d_out; }
+
+private:
+  int d_length;
+  gr_complex d_out, d_out_d1, d_out_d2;
+  std::deque<gr_complex> d_delay_line;
+};
+
+class gr_dc_blocker_cc : public gr_sync_block
+{
+ private:
+  /*!
+   * Build the DC blocker.
+   * \param D          (int) the length of the delay line
+   * \param long_form  (bool) whether to use long (true, default) or short form
+   * \param channel (unsigned integer) Selects the channel to return [default=0].
+   */
+  friend gr_dc_blocker_cc_sptr gr_make_dc_blocker_cc (int D, bool long_form);
+
+  int d_length;
+  bool d_long_form;
+  moving_averager *d_ma_0;
+  moving_averager *d_ma_1;
+  moving_averager *d_ma_2;
+  moving_averager *d_ma_3;
+  std::deque<gr_complex> d_delay_line;
+
+  gr_dc_blocker_cc (int D, bool long_form);
+
+public:
+  ~gr_dc_blocker_cc ();
+
+  /*!
+   * Get the blocker's group delay that is based on length of delay lines
+   */
+  int get_group_delay();
+
+  //int set_length(int D);
+  
+  int work (int noutput_items,
+	    gr_vector_const_void_star &input_items,
+	    gr_vector_void_star &output_items);
+};
+
+#endif
diff --git a/gnuradio-core/src/lib/filter/gr_dc_blocker_cc.i b/gnuradio-core/src/lib/filter/gr_dc_blocker_cc.i
new file mode 100644
index 000000000..b88fecbde
--- /dev/null
+++ b/gnuradio-core/src/lib/filter/gr_dc_blocker_cc.i
@@ -0,0 +1,34 @@
+/* -*- c++ -*- */
+/*
+ * Copyright 2011 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 3, 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., 51 Franklin Street,
+ * Boston, MA 02110-1301, USA.
+ */
+
+GR_SWIG_BLOCK_MAGIC(gr,dc_blocker_cc);
+
+gr_dc_blocker_cc_sptr gr_make_dc_blocker_cc (int D=32, bool long_form=true);
+
+class gr_dc_blocker_cc : public gr_sync_block
+{
+ private:
+  gr_dc_blocker_cc (int D, bool long_form);
+
+ public:
+  ~gr_dc_blocker_cc ();
+};