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## Copyright (C) 2003 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 3 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} =} amodce (@var{x}, @var{Fs}, "amdsb-tc", offset)
## @deftypefnx {Function File} {@var{y} =} amodce (@var{x}, @var{Fs}, "amdsb-sc")
## @deftypefnx {Function File} {@var{y} =} amodce (@var{x}, @var{Fs}, "amssb")
## @deftypefnx {Function File} {@var{y} =} amodce (@var{x}, @var{Fs}, "amssb/time", @var{num}, @var{den})
## @deftypefnx {Function File} {@var{y} =} amodce (@var{x}, @var{Fs}, "qam")
## @deftypefnx {Function File} {@var{y} =} amodce (@var{x}, @var{Fs}, "fm", @var{dev})
## @deftypefnx {Function File} {@var{y} =} amodce (@var{x}, @var{Fs}, "pm", @var{dev})
## @deftypefnx {Function File} {@var{y} =} amodce (@var{x}, [@var{Fs}, @var{iphs}], @dots{})
##
## Baseband modulator for analog signals. The input signal is specified by
## @var{x}, its sampling frequency by @var{Fs} and the type of modulation
## by the third argument, @var{typ}. The default values of @var{Fs} is 1 and
## @var{typ} is "amdsb-tc".
##
## If the argument @var{Fs} is a two element vector, the first element
## represents the sampling rate and the second the initial phase.
##
## The different types of modulations that are available are
##
## @table @asis
## @item "am"
## @itemx "amdsb-tc"
## Double-sideband with carrier
## @item "amdsb-sc"
## Double-sideband with suppressed carrier
## @item "amssb"
## Single-sideband with frequency domain Hilbert filtering
## @item "amssb/time"
## Single-sideband with time domain filtering. Hilbert filter is used by
## default, but the filter can be specified
## @item "qam"
## Quadrature amplitude modulation
## @item "fm"
## Frequency modulation
## @item "pm"
## Phase modulation
## @end table
##
## Additional arguments are available for the modulations "amdsb-tc", "fm",
## "pm" and "amssb/time". These arguments are
##
## @table @code
## @item offset
## The offset in the input signal for the transmitted carrier.
## @item dev
## The deviation of the phase and frequency modulation
## @item num
## @itemx den
## The numerator and denominator of the filter transfer function for the
## time domain filtering of the SSB modulation
## @end table
##
## @seealso{ademodce, dmodce}
## @end deftypefn
function y = amodce (x, Fs, typ, varargin)
if (nargin < 1)
print_usage ();
elseif (nargin < 2)
Fs = 1;
typ = "am";
elseif (nargin < 3)
typ = "am";
endif
if (isempty (Fs))
Fs = 1;
iphs = 0;
elseif (isscalar (Fs))
iphs = 0;
else
if ((max (size (Fs)) != 2) || (min (size (Fs)) != 1))
error ("amodce: sampling frequency must be a scalar or 2-element vector");
endif
Fs = Fs(1);
iphs = Fs(2);
endif
## Pass the optional arguments
offset = min (x(:));
dev = 1;
num = [];
den = [];
narg = 1;
if (!ischar (typ))
error ("amodce: modulation type must be a string");
elseif (strcmp (typ, "am") || strcmp (typ, "amdsb-tc"))
if (length (varargin) > 0)
offset = varargin{1};
narg = narg + 1;
endif
elseif (strcmp (typ, "fm") || strcmp (typ, "pm"))
if (length (varargin) > 0)
dev = varargin{1};
narg = narg + 1;
endif
endif
if (length (varargin) == narg)
error ("amodce: must specify must numerator and denominator of transfer function");
elseif (length (varargin) == narg+1)
num = varargin{narg};
den = varargin{narg+1};
elseif (length (varargin) != narg - 1)
error ("amodce: too many arguments");
endif
if (strcmp (typ, "am") || strcmp (typ, "amdsb-tc"))
y = (x + offset) * exp (1i * iphs);
elseif (strcmp (typ, "amdsb-sc"))
y = x * exp (1i * iphs);
elseif (strcmp (typ, "amssb"))
if (!isreal (x))
error ("amodce: SSB modulated signal must be real");
endif
## Damn, must treat Hilbert transform row-by-row!!!
y = zeros (size (x));
for i = 1:size (x, 2)
y(:,i) = hilbert (x(:,i)) * exp (1i * iphs);
endfor
elseif (strcmp (typ, "amssb/time"))
if (isempty (num) || isempty (dem))
error ("amodce: have not implemented Hilbert transform in time domain yet");
endif
y = zeros (size (x));
for i = 1:size (x, 2)
y(:,i) = filter (num, den, x(:,i));
y(:,i) = (x(:,i) + 1i*y(:,i)) * exp (1i * iphs);
endfor
elseif (strcmp (typ, "qam"))
if (isreal (x))
if (floor (size (x, 2)/2) != (size (x, 2)/2))
error ("amodce: QAM modulation must have an even number of columns for real signals");
endif
y = (x(:,1:2:size (x, 2)) + 1i * x(:,2:2:size (x, 2)));
else
y = x;
endif
y = y * exp (1i * iphs);
elseif (strcmp (typ, "pm"))
y = exp (1i * (dev*x + iphs));
elseif (strcmp (typ, "fm"))
## To convert to PM signal, need to evaluate
## p(t) = \int_0^t dev * x(T) dT
## As x(t) is discrete and not a function, the only way to perform the
## above integration is with Simpson's rule. Note \Delta T = 2 * pi / Fs.
pm = pi / Fs * dev * (cumsum ([zeros(1, size (x, 2)); x(1:size (x, 1) - 1,:)]) ...
+ cumsum (x));
y = exp (1i * (pm + iphs));
else
error ("amodce: unknown modulation specified");
endif
endfunction