X-Git-Url: https://git.creatis.insa-lyon.fr/pubgit/?p=CreaPhase.git;a=blobdiff_plain;f=octave_packages%2Fcommunications-1.1.1%2Fademodce.m;fp=octave_packages%2Fcommunications-1.1.1%2Fademodce.m;h=e610658b27c34330d49803a2490b388c3820015f;hp=0000000000000000000000000000000000000000;hb=f5f7a74bd8a4900f0b797da6783be80e11a68d86;hpb=1705066eceaaea976f010f669ce8e972f3734b05

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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} {@var{y} =} ademodce (@var{x},@var{Fs},'amdsb-tc',offset)
+## @deftypefnx {Function File} {@var{y} =} ademodce (@var{x},@var{Fs},'amdsb-tc/costas',offset)
+## @deftypefnx {Function File} {@var{y} =} ademodce (@var{x},@var{Fs},'amdsb-sc')
+## @deftypefnx {Function File} {@var{y} =} ademodce (@var{x},@var{Fs},'amdsb-sc/costas')
+## @deftypefnx {Function File} {@var{y} =} ademodce (@var{x},@var{Fs},'amssb')
+## @deftypefnx {Function File} {@var{y} =} ademodce (@var{x},@var{Fs},'qam')
+## @deftypefnx {Function File} {@var{y} =} ademodce (@var{x},@var{Fs},'qam/cmplx')
+## @deftypefnx {Function File} {@var{y} =} ademodce (@var{x},@var{Fs},'fm',@var{dev})
+## @deftypefnx {Function File} {@var{y} =} ademodce (@var{x},@var{Fs},'pm',@var{dev})
+## @deftypefnx {Function File} {@var{y} =} ademodce (@var{x},[@var{Fs},@var{iphs}],@var{...})
+## @deftypefnx {Function File} {@var{y} =} ademodce (@var{...},@var{num},@var{den})
+##
+## Baseband demodulator for analog signals. The input signal is specified by
+## @var{x}, its sampling frequency by @var{Fs} and the type of modulation
+## by the third argument, @var{typ}. The default values of @var{Fs} is 1 and 
+## @var{typ} is 'amdsb-tc'.
+##
+## If the argument @var{Fs} is a two element vector, the the first element
+## represents the sampling rate and the second the initial phase.
+##
+## The different types of demodulations that are available are
+##
+## @table @asis
+## @item 'am'
+## @itemx 'amdsb-tc'
+## Double-sideband with carrier
+## @item 'amdsb-tc/costas'
+## Double-sideband with carrier and Costas phase locked loop
+## @item 'amdsb-sc'
+## Double-sideband with suppressed carrier
+## @item 'amssb'
+## Single-sideband with frequency domain Hilbert filtering
+## @item 'qam'
+## Quadrature amplitude demodulation. In-phase in odd-columns and quadrature
+## in even-columns
+## @item 'qam/cmplx'
+## Quadrature amplitude demodulation with complex return value.
+## @item 'fm'
+## Frequency demodulation
+## @item 'pm'
+## Phase demodulation
+## @end table
+##
+## Additional arguments are available for the demodulations 'amdsb-tc', 'fm', 
+## 'pm'. These arguments are
+##
+## @table @code
+## @item offset
+## The offset in the input signal for the transmitted carrier.
+## @item dev
+## The deviation of the phase and frequency modulation
+## @end table
+##
+## It is possible to specify a low-pass filter, by the numerator @var{num} 
+## and denominator @var{den} that will be applied to the returned vector.
+##
+## @end deftypefn
+## @seealso{ademodce,dmodce}
+
+function y = ademodce (x, Fs, typ, varargin)
+
+  if (nargin < 1)
+    help("ademodce");
+  elseif (nargin < 2)
+    Fs = 1;
+    typ = "am";
+  elseif (nargin < 3)
+    typ = "am";
+  endif
+
+  if (isempty(Fs))
+    Fs = 1;
+    iphs = 0;
+  elseif (isscalar(Fs))
+    iphs = 0;
+  else
+    if ((max(size(Fs)) != 2) || (min(size(Fs)) != 1))
+      error ("ademodce: sampling frequency must be a scalar or 2-element vector");
+    endif
+    Fs = Fs(1);
+    iphs = Fs(2);
+  endif
+
+  ## Pass the optional arguments
+  dev = 1;
+  num = [];
+  den = [];
+  narg = 1;
+  if (!ischar(typ))
+    error ("ademodce: modulation type must be a string");
+  elseif (strcmp(typ,"am") || strcmp(typ,"amdsb-tc"))
+    if (length(varargin) > 0)
+      offset = varargin{1};
+      narg = narg + 1;
+    endif
+  elseif (strcmp(typ,"fm") || strcmp(typ,"pm"))
+    if (length(varargin) > 0)
+      dev = varargin{1};
+      narg = narg + 1;
+    endif
+  endif    
+  if (length(varargin) == narg)
+    error ("ademodce: must specify must numerator and denominator of transfer function");
+  elseif (length(varargin) == narg+1)
+    num = varargin{narg};
+    den = varargin{narg+1};
+  elseif (length(varargin) != narg - 1)
+    error ("ademodce: too many arguments");
+  endif
+
+  if (strcmp(typ,"am") || findstr(typ,"amdsb-tc"))
+    if (findstr(typ,"/costas"))
+      error ("ademodce: Costas phase locked loop not implemented");
+    endif
+    y = real(x * exp(-1i * iphs));
+    if (exist("offset","var"))
+      y = y - offset;
+    else
+      if (min(size(y)) == 1)
+	      y = y - mean(y);
+      else
+	      for i=1:size(y,2)
+	        y(:,i) = y(:,i) - mean(y(:,i));
+	      end
+      endif
+    endif
+  elseif (strcmp(typ,"amdsb-sc"))
+    y = real(x * exp(-1i * iphs));
+  elseif (findstr(typ,"amssb"))
+    if (findstr(typ,"/costas"))
+      error ("ademodce: Costas phase locked loop not implemented");
+    endif
+    y = real(x * exp(-1i * iphs));
+  elseif (strcmp(typ,"qam"))
+    y1 = x * exp(-1i * iphs);
+    y = zeros(size(y1,1),2*size(y1,2));
+    y(:,1:2:size(y,2)) = real(y1);
+    y(:,2:2:size(y,2)) = imag(y1);
+  elseif (strcmp(typ,"qam/cmplx"))
+    y = x * exp(-1i * iphs);
+  elseif (strcmp(typ,"pm"))
+    y = ( -1i * log(x) + iphs) / dev;
+  elseif (strcmp(typ,"fm"))
+    ## This can't work as it doesn't take into account the
+    ## phase wrapping in the modulation process. Therefore 
+    ## we'll get some of the demodulated values in error, with
+    ## most of the values being correct..
+    ##
+    ## Not sure the best approach to fixing this. Perhaps implement
+    ## a PLL with the ouput of the phase detector being the demodulated
+    ## signal...
+    warning("ademodce: FM demodulation broken!!")
+    pm = Fs / dev / pi * ( - 1i * log(x) + iphs)
+    y = [pm(:,1), (pm(:,2:size(pm,2)) - pm(:,1:size(pm,2)-1))]; 
+  else
+    error ("ademodce: unknown demodulation specified");
+  endif
+
+  if (!isempty(num) && !isempty(dem))
+    ## Low-pass filter the output
+    if (min(size(y)) == 1)
+      y = filter(num,den, y);
+    else    
+      for i=1:size(y,2)
+	      y(:,i) = filter(num, den, y(:,i));
+      end
+    endif
+  endif
+
+endfunction
+