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/*!
* \file
* \brief Implementation of some specific functions useful in communications
* \author Tony Ottosson and Erik G. Larsson
*
* -------------------------------------------------------------------------
*
* IT++ - C++ library of mathematical, signal processing, speech processing,
* and communications classes and functions
*
* Copyright (C) 1995-2008 (see AUTHORS file for a list of contributors)
*
* This program 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 of the License, or
* (at your option) any later version.
*
* This program 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 this program; if not, write to the Free Software
* Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
*
* -------------------------------------------------------------------------
*/
#include <itpp/comm/commfunc.h>
#include <itpp/base/converters.h>
#include <itpp/base/specmat.h>
#include <itpp/base/matfunc.h>
#include <itpp/base/binary.h>
#include <itpp/base/sort.h>
namespace itpp {
bmat graycode(int m)
{
if (m == 1) {
smat temp = "0;1";
return to_bmat(temp);
} else {
bvec temp(1<<(m-1));
bmat bb = graycode(m-1);
bmat out(1<<m, m);
out.zeros();
out.set_col(0, concat(zeros_b(1<<(m-1)), ones_b(1<<(m-1))) );
for (int i=0; i<m-1; i++) {
temp = bb.get_col(i);
out.set_col(i+1, concat(temp, reverse(temp)) );
}
return out;
}
}
int hamming_distance(const bvec &a, const bvec &b)
{
int i, n=0;
it_assert_debug(a.size() == b.size(), "hamming_distance()");
for (i=0; i<a.size(); i++)
if (a(i) != b(i))
n++;
return n;
}
int weight(const bvec &a)
{
int i, n=0;
for (i=0; i<a.size(); i++)
if (a(i)==bin(1))
n++;
return n;
}
vec waterfilling(const vec &alpha, double P) // added by EGL April 2007
{
int n=length(alpha);
it_assert(n > 0, "waterfilling(): alpha vector cannot have zero length");
it_assert(P > 0, "waterfilling(): Power constraint must be positive");
ivec ind=sort_index(alpha); // indices in increasing order
it_assert(alpha(ind(0)) > 0, "waterfilling(): Gains must be positive");
// find lambda
double lambda = 0.0;
for (int m=0; m<n; m++) {
// try m,...,n-1 nonzero allocation
double t=0;
for (int j=m; j<n; j++) {
t+=1.0/alpha(ind(j));
}
t=(t+P)/(n-m);
lambda=1.0/t;
if (lambda < alpha(ind(m)))
break;
}
vec result(n);
for (int j=0; j<n; j++) {
result(j) = ((lambda < alpha(j)) ? (1.0/lambda - 1.0/alpha(j)) : 0.0);
}
return result;
}
} // namespace itpp
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