## 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 complex-baseband phase shift keying modulated signal
## 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-PSK is
##
## @example
## @group
## d = randint (1, 1e3, 8);
## y = pskmod (d, 8, 0, "gray");
## z = awgn (y, 20);
## d_est = pskdemod (z, 8, 0, "gray");
## plot (z, "rx")
## biterr (d, d_est)
## @end group
## @end example
## @seealso{pskmod}
## @end deftypefn

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

  if (nargin < 2)
    print_usage ();
  endif

  if (nargin < 3)
    phi = 0;
  endif

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

  m = 0:M-1;
  index = mod (round ((arg (x) - phi) * M/2/pi), M) + 1;

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

endfunction

%!assert (pskdemod ([1 j -1 -j], 4, 0, "Bin"), [0:3])
%!assert (pskdemod ([1 j -j -1], 4, 0, "Gray"), [0:3])

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