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pskdemod.m

## 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 2, 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; see the file COPYING.  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
## @end deftypefn
## @seealso{pskmod}

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

if nargin<2
      usage("y = pskdemod (x, M, [phi, [type]])");   
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
    usage("y = pskdemod (x, M, [phi, [type]])");   
endif

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

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