octave-communications-common 1.2.1-1build1 / usr / share / octave / packages / communications-1.2.1 / amodce.m

## 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: FS must be a scalar or a 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 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: Hilbert transform in time domain not yet implemented");
    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))
      xc = columns (x);
      if (xc/2 != fix (xc/2))
        error ("amodce: QAM modulation must have an even number of columns for real signals");
      endif
      y = (x(:,1:2:xc) + 1i * x(:,2:2:xc));
    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 '%s'", typ);
  endif

endfunction

%% Test input validation
%!error amodce ()
%!error amodce (1, 2, "invalid")
%!error amodce (1, 2, "am", 3, 4, 5, 6)