## Copyright (C) 2006 Charalampos C. Tsimenidis
##
## 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} =} pamdemod (@var{x}, @var{m})
## @deftypefnx {Function File} {@var{y} =} pamdemod (@var{x}, @var{m}, @var{phi})
## @deftypefnx {Function File} {@var{y} =} pamdemod (@var{x}, @var{m}, @var{phi}, @var{type})
##
## Demodulates a pulse amplitude modulated signal @var{x} into an
## information sequence of integers in the range @code{[0 @dots{} M-1]}.
## @var{phi} controls the initial phase and @var{type} controls the
## constellation mapping. If @var{type} is set to "Bin" will result in
## binary encoding, in contrast, if set to "Gray" will give Gray encoding.
## An example of Gray-encoded 8-PAM is
##
## @example
## @group
## d = randint (1, 1e4, 8);
## y = pammod (d, 8, 0, "gray");
## z = awgn (y, 20);
## d_est = pamdemod (z, 8, 0, "gray");
## plot (z, "rx")
## biterr (d, d_est)
## @end group
## @end example
## @seealso{pammod}
## @end deftypefn

function y = pamdemod (x, M, phi, type)

  if (nargin < 2)
    print_usage ();
  endif

  if (nargin < 3)
    phi = 0;
  endif

  if (nargin < 4)
    type = "Bin";
  endif

  index = genqamdemod (x, [-M+1:2:M-1] .* exp (-1j*phi));

  if (strcmp (type, "Bin") || strcmp (type, "bin"))
    y = index;
  elseif (strcmp (type, "Gray") || strcmp (type, "gray"))
    m = 0:M-1;
    map = bitxor (m, bitshift (m, -1));
    y = map(index+1);
  else
    print_usage ();
  endif

endfunction

%!assert (pamdemod ([-7:2:7], 8, 0, "Bin"), [0:7])
%!assert (pamdemod ([-7:2:7], 8, 0, "Gray"), [0 1 3 2 6 7 5 4])

%% Test input validation
%!error pamdemod ()
%!error pamdemod (1)
%!error pamdemod (1, 2, 3, "invalid")
