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+/* -*- c++ -*- */
+/*
+ * Copyright 2011,2012 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.h>
+#include <stdexcept>
+#include <cstdio>
+
+namespace gr {
+ namespace digital {
+
+ mpsk_snr_est::mpsk_snr_est(double alpha)
+ {
+ set_alpha(alpha);
+ }
+
+ mpsk_snr_est::~mpsk_snr_est()
+ {}
+
+ void
+ mpsk_snr_est::set_alpha(double alpha)
+ {
+ d_alpha = alpha;
+ d_beta = 1.0-alpha;
+ }
+
+ double
+ mpsk_snr_est::alpha() const
+ {
+ return d_alpha;
+ }
+
+ int
+ mpsk_snr_est::update(int noutput_items,
+ const gr_complex *input)
+ {
+ throw std::runtime_error("mpsk_snr_est: Unimplemented");
+ }
+
+ double
+ mpsk_snr_est::snr()
+ {
+ throw std::runtime_error("mpsk_snr_est: Unimplemented");
+ }
+
+
+ /*****************************************************************/
+
+
+ mpsk_snr_est_simple::mpsk_snr_est_simple(double alpha) :
+ mpsk_snr_est(alpha)
+ {
+ d_y1 = 0;
+ d_y2 = 0;
+ }
+
+ int
+ mpsk_snr_est_simple::update(int noutput_items,
+ const gr_complex *input)
+ {
+ for(int i = 0; i < noutput_items; i++) {
+ double y1 = abs(input[i]);
+ d_y1 = d_alpha*y1 + d_beta*d_y1;
+
+ double y2 = real(input[i]*input[i]);
+ d_y2 = d_alpha*y2 + d_beta*d_y2;
+ }
+ return noutput_items;
+ }
+
+ double
+ mpsk_snr_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);
+ }
+
+
+ /*****************************************************************/
+
+
+ mpsk_snr_est_skew::mpsk_snr_est_skew(double alpha) :
+ mpsk_snr_est(alpha)
+ {
+ d_y1 = 0;
+ d_y2 = 0;
+ d_y3 = 0;
+ }
+
+ int
+ mpsk_snr_est_skew::update(int noutput_items,
+ const gr_complex *input)
+ {
+ for(int i = 0; i < noutput_items; i++) {
+ double y1 = abs(input[i]);
+ d_y1 = d_alpha*y1 + d_beta*d_y1;
+
+ double y2 = real(input[i]*input[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(input[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
+ mpsk_snr_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));
+ }
+
+
+ /*****************************************************************/
+
+
+ mpsk_snr_est_m2m4::mpsk_snr_est_m2m4(double alpha) :
+ mpsk_snr_est(alpha)
+ {
+ d_y1 = 0;
+ d_y2 = 0;
+ }
+
+ int
+ mpsk_snr_est_m2m4::update(int noutput_items,
+ const gr_complex *input)
+ {
+ for(int i = 0; i < noutput_items; i++) {
+ double y1 = abs(input[i])*abs(input[i]);
+ d_y1 = d_alpha*y1 + d_beta*d_y1;
+
+ double y2 = abs(input[i])*abs(input[i])*abs(input[i])*abs(input[i]);
+ d_y2 = d_alpha*y2 + d_beta*d_y2;
+ }
+ return noutput_items;
+ }
+
+ double
+ mpsk_snr_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)));
+ }
+
+
+ /*****************************************************************/
+
+
+ snr_est_m2m4::snr_est_m2m4(double alpha, double ka, double kw) :
+ mpsk_snr_est(alpha)
+ {
+ d_y1 = 0;
+ d_y2 = 0;
+ d_ka = ka;
+ d_kw = kw;
+ }
+
+ int
+ snr_est_m2m4::update(int noutput_items,
+ const gr_complex *input)
+ {
+ for(int i = 0; i < noutput_items; i++) {
+ double y1 = abs(input[i])*abs(input[i]);
+ d_y1 = d_alpha*y1 + d_beta*d_y1;
+
+ double y2 = abs(input[i])*abs(input[i])*abs(input[i])*abs(input[i]);
+ d_y2 = d_alpha*y2 + d_beta*d_y2;
+ }
+ return noutput_items;
+ }
+
+ double
+ snr_est_m2m4::snr()
+ {
+ double M2 = d_y1;
+ double M4 = d_y2;
+ double s = M2*(d_kw - 2) +
+ sqrt((4.0-d_ka*d_kw)*M2*M2 + M4*(d_ka+d_kw-4.0)) /
+ (d_ka + d_kw - 4.0);
+ double n = M2 - s;
+
+ return 10.0*log10(s / n);
+ }
+
+
+ /*****************************************************************/
+
+
+ mpsk_snr_est_svr::mpsk_snr_est_svr(double alpha) :
+ mpsk_snr_est(alpha)
+ {
+ d_y1 = 0;
+ d_y2 = 0;
+ }
+
+ int
+ mpsk_snr_est_svr::update(int noutput_items,
+ const gr_complex *input)
+ {
+ for(int i = 0; i < noutput_items; i++) {
+ double x = abs(input[i]);
+ double x1 = abs(input[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
+ mpsk_snr_est_svr::snr()
+ {
+ double x = d_y1 / (d_y2 - d_y1);
+ return 10.0*log10(2.*((x-1) + sqrt(x*(x-1))));
+ }
+
+ } /* namespace digital */
+} /* namespace gr */