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wgn.m

## Copyright (C) 2002 David Bateman
##
## 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, see <http://www.gnu.org/licenses/>.

## -*- texinfo -*-
## @deftypefn {Function File} {@var{y} =} wgn (@var{m},@var{n},@var{p})
## @deftypefnx {Function File} {@var{y} =} wgn (@var{m},@var{n},@var{p},@var{imp})
## @deftypefnx {Function File} {@var{y} =} wgn (@var{m},@var{n},@var{p},@var{imp},@var{seed},)
## @deftypefnx {Function File} {@var{y} =} wgn (@var{...},'@var{type}')
## @deftypefnx {Function File} {@var{y} =} wgn (@var{...},'@var{output}')
##
## Returns a M-by-N matrix @var{y} of white Gaussian noise. @var{p} specifies
## the power of the output noise, which is assumed to be referenced to an
## impedance of 1 Ohm, unless @var{imp} explicitly defines the impedance. 
##
## If @var{seed} is defined then the randn function is seeded with this
## value.
##
## The arguments @var{type} and @var{output} must follow the above numerial
## arguments, but can be specified in any order. @var{type} specifies the
## units of @var{p}, and can be 'dB', 'dBW', 'dBm' or 'linear'. 'dB' is
## in fact the same as 'dBW' and is keep as a misnomer of Matlab. The
## units of 'linear' are in Watts.
##
## The @var{output} variable should be either 'real' or 'complex'. If the 
## output is complex then the power @var{p} is divided equally betwen the
## real and imaginary parts.
##
## @seealso{randn,awgn}
## @end deftypefn

## 2003-01-28
##   initial release

function y = wgn (m, n, p, varargin)

  if ((nargin < 3) || (nargin > 7))
    error ("usage: wgn(m, n, p, imp, seed, type, output)");
  endif
    
  if (!isscalar(m) || !isreal(m) || (m < 0) || !isscalar(n) || ...
      !isreal(n) || (n<0))
    error ("wgn: matrix dimension error");
  endif
  
  type = "dBW";
  out = "real";
  imp = 1;
  seed = [];
  narg = 0;

  for i=1:length(varargin)
    arg = varargin{i};
    if (ischar(arg))
      if (strcmp(arg,"real"))
        out = "real";  
      elseif (strcmp(arg,"complex"))
        out = "complex";  
      elseif (strcmp(arg,"dB"))
        type = "dBW";  
      elseif (strcmp(arg,"dBW"))
        type = "dBW";  
      elseif (strcmp(arg,"dBm"))
        type = "dBm";  
      elseif (strcmp(arg,"linear"))
        type = "linear";  
      else
        error ("wgn: invalid argument");
      endif
    else
      narg++;
      switch (narg)
      case 1,
        imp = arg;
      case 2,
        seed = arg;
      otherwise
        error ("wgn: too many arguments");
      endswitch
    endif
  end

  if (isempty(imp))
    imp = 1;
  elseif (!isscalar(imp) || !isreal(imp) || (imp < 0))
    error ("wgn: impedance value illegal");
  endif

  if (!isempty(seed))
    if (!isscalar(seed) || !isreal(seed) || (seed < 0) || 
      ((seed-floor(seed)) != 0))
      error ("wgn: random seed must be integer");
    endif
  endif
    
  if (!isscalar(p) || !isreal(p))
    error("wgn: invalid power");
  endif
  if (strcmp(type,"linear") && (p < 0))
    error("wgn: invalid power");
  endif

  if (strcmp(type,"dBW"))
    np = 10 ^ (p/10);
  elseif (strcmp(type,"dBm"))
    np = 10 ^((p - 30)/10);
  elseif (strcmp(type,"linear"))
    np = p;
  endif

  if(!isempty(seed))
    randn("state",seed);
  endif

  if (strcmp(out,"complex"))
    y = (sqrt(imp*np/2))*(randn(m,n)+1i*randn(m,n));
  else
    y = (sqrt(imp*np))*randn(m,n);
  endif
  
endfunction

## Allow 30% error in standard deviation, due to randomness
%!error wgn ();
%!error wgn (1);
%!error wgn (1,1);
%!error wgn (1,1,1,1,1,1);
%!assert (isreal(wgn(10,10,30,1,"dBm","real")));
%!assert (iscomplex(wgn(10,10,30,1,"dBm","complex")));
%!assert (abs(std(wgn(10000,1,30,1,"dBm")) - 1) < 0.3);
%!assert (abs(std(wgn(10000,1,0,1,"dBW")) - 1) < 0.3);
%!assert (abs(std(wgn(10000,1,1,1,"linear")) - 1) < 0.3);

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