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pamdemod.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 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
## @end deftypefn
## @seealso{pammod}

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

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

%!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])

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