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## Copyright (C) 2003 David Bateman
##
## 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} {z = } demodmap (@var{y},@var{fd},@var{fs},'ask',@var{m})
## @deftypefnx {Function File} {z = } demodmap (@var{y},@var{fd},@var{fs},'fsk',@var{m},@var{tone})
## @deftypefnx {Function File} {z = } demodmap (@var{y},@var{fd},@var{fs},'msk')
## @deftypefnx {Function File} {z = } demodmap (@var{y},@var{fd},@var{fs},'psk',@var{m})
## @deftypefnx {Function File} {z = } demodmap (@var{y},@var{fd},@var{fs},'qask',@var{m})
## @deftypefnx {Function File} {z = } demodmap (@var{y},@var{fd},@var{fs},'qask/cir',@var{nsig},@var{amp},@var{phs})
## @deftypefnx {Function File} {z = } demodmap (@var{y},@var{fd},@var{fs},'qask/arb',@var{inphase},@var{quadr})
## @deftypefnx {Function File} {z = } demodmap (@var{y},@var{fd},@var{fs},'qask/arb',@var{map})
## @deftypefnx {Function File} {z = } demodmap (@var{y},[@var{fd}, @var{off}],@var{...})
##
## Demapping of an analog signal to a digital signal. The function
## @dfn{demodmap} must have at least three input arguments and one
## output argument. Argument @var{y} is a complex variable representing
## the analog signal to be demapped. The variables @var{fd} and @var{fs} are
## the sampling rate of the of digital signal and the sampling rate of the
## analog signal respectively. It is required that @code{@var{fs}/@var{fd}}
## is an integer.
##
## The available mapping of the digital signal are
##
## @table @asis
## @item 'ask'
## Amplitude shift keying
## @item 'fsk'
## Frequency shift keying
## @item 'msk'
## Minimum shift keying
## @item 'psk'
## Phase shift keying
## @item 'qask'
## @itemx 'qsk'
## @itemx 'qam'
## Quadraure amplitude shift keying
## @end table
##
## In addition the 'qask', 'qsk' and 'qam' method can be modified with the
## flags '/cir' or '/arb'. That is 'qask/cir' and 'qask/arb', etc are valid
## methods and give circular- and arbitrary-qask mappings respectively. Also
## the method 'fsk' and 'msk' can be modified with the flag '/max', in
## which case @var{y} is assumed to be a matrix with @var{m} columns,
## representing the symbol correlations.
##
## The variable @var{m} is the order of the modulation to use. By default
## this is 2, and in general should be specified.
##
## For 'qask/cir', the additional arguments are the same as for
## @dfn{apkconst}, and you are referred to @dfn{apkconst} for the definitions
## of the additional variables.
##
## For 'qask/arb', the additional arguments @var{inphase} and @var{quadr} give
## the in-phase and quadrature components of the mapping, in a similar mapping
## to the outputs of @dfn{qaskenco} with one argument. Similar @var{map}
## represents the in-phase and quadrature components of the mapping as
## the real and imaginary parts of the variable @var{map}.
## @seealso{modmap, ddemodce, ademodce, apkconst, qaskenco}
## @end deftypefn
function z = demodmap (y, fd, fs, varargin)
if (nargin < 3)
print_usage ();
endif
if (!isscalar(fs) || !isreal(fs) || !isreal(fd) ||(fs <= 0) || (fd <= 0))
error ("demodmap: sampling rates must be positive real values");
endif
if (abs(fs/fd - floor(fs/fd)) > eps)
error ("demodmap: the sample rate Fs must be an integer multiple of Fd");
endif
if (!isscalar(fd))
if (isequal(size(fd),[1,2]))
off = fd(2);
fd = fd(1);
else
error ("demodmap: sampling rate Fd must be a scalar or two-element row-vector");
endif
else
off = 0;
endif
if (nargin > 3)
method = varargin{1};
if (!ischar(method) || (!strcmp(method,"ask") && ...
isempty(findstr(method,"msk")) && isempty(findstr(method,"fsk")) && ...
isempty(findstr(method,"samp")) && !strcmp(method,"psk") && ...
!strcmp(method,"qask") && !strcmp(method,"qam") && ...
!strcmp(method,"qsk") && !strcmp(method,"qask/cir") && ...
!strcmp(method,"qam/cir") && !strcmp(method,"qsk/cir") && ...
!strcmp(method,"qask/arb") && !strcmp(method,"qam/arb") && ...
!strcmp(method,"qsk/arb")))
error ("modmap: unknown mapping method");
endif
else
method = "sample";
endif
if (!isreal(off) || (off < 0) || (off != floor(off)) || ...
(off >= fs/fd))
error ("demodmap: offset must be an integer in the range [0, Fs/Fd)");
endif
if (off == 0)
off = round(fs/fd);
endif
if (min(size(y)) == 1)
y = y(off:round(fs/fd):length(y));
else
y = y(off:round(fs/fd):size(y,1),:);
endif
if (strcmp(method,"ask") || !isempty(findstr(method,"fsk")) || ...
strcmp(method,"psk") || strcmp(method,"qask") || ...
strcmp(method,"qam") || strcmp(method,"qsk"))
if (nargin > 4)
M = varargin{2};
else
M = 2;
endif
if (!isempty(findstr(method,"fsk")) && (nargin > 5))
error ("demodmap: too many arguments");
endif
endif
z = [];
if (!isempty(findstr(method,"fsk")) || !isempty(findstr(method,"msk")))
if (findstr(method,"msk"))
if (nargin > 4)
error ("demodmap: too many arguments");
endif
M = 2;
tone = fd/2;
else
if (nargin > 5)
tone = varargin{3};
else
tone = fd;
endif
if (nargin > 6)
error ("demodmap: too many arguments");
endif
endif
if (findstr(method,"/max"))
if (size(y,2) != M)
error ("demodmap: when using correlation must have M columns");
endif
## We have an M-column maximum from which with pick index of the maximum
## value in each row as the decoded value
[a, b] = max(y');
z = (b - 1)';
else
c = [0:M-1]*tone;
endif
elseif (strcmp(method,"ask"))
if (floor(M/2) == M/2)
c = [ -2*([M/2:-1:1]-0.5)/(M-1), 2*([1:M/2]-0.5)/(M-1)];
else
c = [ -2*([floor(M/2):-1:1])/(M-1), 0, 2*([1:floor(M/2)])/(M-1)];
endif
elseif (strcmp(method,"psk"))
c = apkconst(M,[],[]);
elseif (!isempty(findstr(method,"qask")) || ...
!isempty(findstr(method,"qsk")) || ...
!isempty(findstr(method,"qam")))
if (findstr(method,"/cir"))
nsig = 2;
amp = [];
phs = [];
if (nargin > 4)
nsig = varargin{2};
if (!isvector(nsig))
error ("modmap: invalid number of constellation point in qask/cir");
endif
endif
if (nargin > 5)
amp = varargin{3};
endif
if (nargin > 6)
phs = varargin{4};
endif
c = apkconst(nsig,amp,phs);
M = length(c);
elseif (findstr(method,"/arb"))
if (nargin == 4)
c = qaskenco(2);
elseif (nargin == 5)
c = varargin{2};
elseif (nargin == 6)
inphase = varargin{2};
quadr = varargin{3};
c = inphase + 1i*quadr;
elseif (nargin > 6)
error ("demodmap: too many arguments");
endif
M = length(c);
else
## Could do "c = qaskenco(M)", but qaskdeco's speed is not dependent
## on M, while speed of code below is O(M).
z = qaskdeco(y,M);
endif
endif
## Have we decoded yet? If not have a mapping that we can use.
if (isempty(z))
c = c(:);
z = zeros(size(y));
if (size(y,1) == 1)
[a, b] = min(abs(repmat(y(:).',M,1) - repmat(c,1,size(y,2))));
z = b - 1;
elseif (size(y,1) == 1)
[a, b] = min(abs(repmat(y(:),M,1) - repmat(c,1,size(y,1))));
z = (b - 1).';
else
for i=1:size(y,1)
[a, b] = min(abs(repmat(y(i,:),M,1) - repmat(c,1,size(y,2))));
z(i,:) = b - 1;
endfor
endif
endif
endfunction