digital: added a class, digital_mpsk_snr_est_cc, that estimates the SNR of an M-ary PSK signal.

This block can calculate the SNR using 1 of 4 different methods specified in the block's constructor. They (tend to) trade off accuracy for computational performnace.

1 files changed, 226 insertions, 0 deletions

diff --git a/gr-digital/lib/digital_mpsk_snr_est_cc.cc b/gr-digital/lib/digital_mpsk_snr_est_cc.cc
new file mode 100644
index 000000000..7793eed1d
--- /dev/null
+++ b/gr-digital/lib/digital_mpsk_snr_est_cc.cc
@@ -0,0 +1,226 @@
+/* -*- 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 <digital_mpsk_snr_est_cc.h>
+#include <gr_io_signature.h>
+#include <cstdio>
+
+digital_mpsk_snr_est_cc_sptr
+digital_make_mpsk_snr_est_cc(snr_est_type_t type,
+			     double alpha)
+{
+  return gnuradio::get_initial_sptr(new digital_mpsk_snr_est_cc(type, alpha));
+}
+
+digital_mpsk_snr_est_cc::digital_mpsk_snr_est_cc(snr_est_type_t type,
+						 double alpha)
+  : gr_sync_block ("mpsk_snr_est_cc",
+		   gr_make_io_signature(1, 1, sizeof(gr_complex)),
+		   gr_make_io_signature(1, 1, sizeof(gr_complex))),
+    d_type(type), d_y1(0), d_y2(0), d_y3(0), d_y4(0)
+{
+  set_type(type);
+  set_alpha(alpha);
+  set_history(2);
+}
+
+digital_mpsk_snr_est_cc::~digital_mpsk_snr_est_cc()
+{
+}
+
+int
+digital_mpsk_snr_est_cc::est_simple(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];
+
+  for (int i = 0; i < noutput_items; i++){
+    double y1 = abs(in[i]);
+    d_y1 = d_alpha*y1 + d_beta*d_y1;
+
+    double y2 = real(in[i]*in[i]);
+    d_y2 = d_alpha*y2 + d_beta*d_y2;
+  }
+  return noutput_items;
+}
+
+double
+digital_mpsk_snr_est_cc::est_simple_snr()
+{
+  double y1_2 = d_y1*d_y1;
+  double y3 = y1_2 - d_y2 + 1e-20;
+  return 10.0*log10(y1_2/y3);
+}
+
+int
+digital_mpsk_snr_est_cc::est_skew(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];
+
+  for (int i = 0; i < noutput_items; i++){
+    double y1 = abs(in[i]);
+    d_y1 = d_alpha*y1 + d_beta*d_y1;
+
+    double y2 = real(in[i]*in[i]);
+    d_y2 = d_alpha*y2 + d_beta*d_y2;
+
+    // online algorithm for calculating skewness
+    // See:
+    // http://en.wikipedia.org/wiki/Algorithms_for_calculating_variance#Higher-order_statistics
+    double d = abs(in[i]) - d_y1;
+    double d_i = d / (i+1);
+    double y3 = (d*d_i*i)*d_i*(i-1) - 3.0*d_i*d_y2;
+    d_y3 = d_alpha*y3 + d_beta*d_y3;
+  }
+  return noutput_items;
+}
+
+double
+digital_mpsk_snr_est_cc::est_skew_snr()
+{
+  double y3 = d_y3*d_y3 / (d_y2*d_y2*d_y2);
+  double y1_2 = d_y1*d_y1;
+  double x = y1_2 - d_y2;
+  return 10.0*log10(y1_2 / (x + y3*y1_2));
+}
+
+int
+digital_mpsk_snr_est_cc::est_m2m4(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];
+
+  for (int i = 0; i < noutput_items; i++){
+    double y1 = abs(in[i])*abs(in[i]);
+    d_y1 = d_alpha*y1 + d_beta*d_y1;
+
+    double y2 = abs(in[i])*abs(in[i])*abs(in[i])*abs(in[i]);
+    d_y2 = d_alpha*y2 + d_beta*d_y2;
+  }
+  return noutput_items;
+}
+
+double
+digital_mpsk_snr_est_cc::est_m2m4_snr()
+{
+  double y1_2 = d_y1*d_y1;
+  return 10.0*log10(2.0*sqrt(2*y1_2 - d_y2) / (d_y1 - sqrt(2*y1_2 - d_y2)));
+}
+
+
+int
+digital_mpsk_snr_est_cc::est_svn(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];
+
+  for (int i = 0; i < noutput_items; i++){
+    double x = abs(in[i]);
+      double x1 = abs(in[i-1]);
+    double y1 = (x*x)*(x1*x1);
+    d_y1 = d_alpha*y1 + d_beta*d_y1;
+    
+    double y2 = x*x*x*x;
+    d_y2 = d_alpha*y2 + d_beta*d_y2;
+  }
+  return noutput_items;
+}
+
+double
+digital_mpsk_snr_est_cc::est_svn_snr()
+{
+  double x = d_y1 / (d_y2 - d_y1);
+  return 10.0*log10(2.*((x-1) + sqrt(x*(x-1))));
+}
+
+int
+digital_mpsk_snr_est_cc::work(int noutput_items,
+			      gr_vector_const_void_star &input_items,
+			      gr_vector_void_star &output_items)
+{
+  return (*this.*d_estimator)(noutput_items, input_items, output_items);
+}
+
+double
+digital_mpsk_snr_est_cc::snr()
+{
+  return (*this.*d_calculator)();
+}
+
+snr_est_type_t
+digital_mpsk_snr_est_cc::type() const
+{
+  return d_type;
+}
+
+double
+digital_mpsk_snr_est_cc::alpha() const
+{
+  return d_alpha;
+}
+
+void
+digital_mpsk_snr_est_cc::set_type(snr_est_type_t t)
+{
+  d_type = t;
+  d_y1 = 0;
+  d_y2 = 0;
+  d_y3 = 0;
+  d_y4 = 0;
+
+  switch (d_type) {
+  case(SNR_EST_SIMPLE):
+    d_estimator = &digital_mpsk_snr_est_cc::est_simple;
+    d_calculator = &digital_mpsk_snr_est_cc::est_simple_snr;
+    break;
+  case(SNR_EST_SKEW):
+    d_estimator = &digital_mpsk_snr_est_cc::est_skew;
+    d_calculator = &digital_mpsk_snr_est_cc::est_skew_snr;
+    break;
+  case(SNR_EST_M2M4):
+    d_estimator = &digital_mpsk_snr_est_cc::est_m2m4;
+    d_calculator = &digital_mpsk_snr_est_cc::est_m2m4_snr;
+    break;
+  case(SNR_EST_SVN):
+    d_estimator = &digital_mpsk_snr_est_cc::est_svn;
+    d_calculator = &digital_mpsk_snr_est_cc::est_svn_snr;
+    break;
+  default:
+    throw std::invalid_argument("digital_mpsk_snr_est_cc: unknown type specified.\n");
+  }
+}
+
+void
+digital_mpsk_snr_est_cc::set_alpha(double alpha)
+{
+  d_alpha = alpha;
+  d_beta = 1.0-alpha;
+}