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## 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])