dpskdemod.m

这里有DPSK的解调源代码

function z = dpskdemod(y,M,varargin)
% DPSKDEMOD Differential phase shift keying demodulation.
%   Z = DPSKDEMOD(Y,M) demodulates the complex envelope Y of a DPSK
%   modulated signal. M is the alphabet size and must be an integer. For
%   two-dimensional signals, the function treats each column as 1 channel.
%
%   Z = DPSKDEMOD(Y,M,PHASEROT) specifies the phase rotation (rad). In this
%   case, the total per-symbol phase shift is the sum of PHASEROT and the
%   phase generated by the differential modulation.
%
%   Z = DPSKDEMOD(X,M,PHASEROT,SYMBOL_ORDER) specifies how the function 
%   assigns binary words to corresponding integers. If SYMBOL_ORDER is set 
%   to 'bin' (default), then the function uses a natural binary-coded ordering.  
%   If SYMBOL_ORDER is set to 'gray', then the function uses a Gray-coded ordering.
%
%   See also DPSKMOD, PSKDEMOD, PSKMOD. 

%    Copyright 1996-2005 The MathWorks, Inc. 
%    $Revision: 1.1.6.5 $  $Date: 2004/12/10 19:22:25 $ 

% error checks
if(nargin<2)
    error('comm:dpskdemod:numarg','Too few input arguments.');
end

if(nargin>4)
    error('comm:dpskdemod:numarg','Too many input arguments.');
end

%Check y, phase, Symbol set ordering
if( ~isnumeric(y))
    error('comm:dpskdemod:Ynum','Y must be numeric.');
end

if(~isreal(M) || ~isscalar(M) || M<=0 || (ceil(M)~=M) || ~isnumeric(M) )
    error('comm:dpskdemod:Mreal','M must be a scalar positive integer.');
end

if(nargin==2 || isempty(varargin{1}) )    
   Phase_Rotation = 0;
else
    Phase_Rotation = varargin{1};
    if(~isreal(Phase_Rotation) || ~isscalar(Phase_Rotation)|| ~isnumeric(Phase_Rotation) )
        error('comm:dpskdemod:phaserotReal','PHASEROT must be a real scalar.');    
    end
end

% Check SYMBOL_ORDER
if(nargin==2 || nargin==3 )    
   Symbol_Ordering = 'bin'; % default
else
    Symbol_Ordering = varargin{2};
    if (~ischar(Symbol_Ordering)) || (~strcmpi(Symbol_Ordering,'GRAY')) && (~strcmpi(Symbol_Ordering,'BIN'))
        error('comm:dpskdemod:SymbolOrder','Invalid symbol set ordering.');    
    end
end


% --- Assure that Y, if one dimensional, has the correct orientation --- %
wid = size(y,1);
if(wid ==1)
    y = y(:);
end

%create the map
modmap = 2*pi*(0:M-1)/M + Phase_Rotation;

%get the phase difference
ang = diff(unwrap(angle(y)));

%adjust the negative angles to be positive instead
ind = find(ang < -(pi/M - Phase_Rotation/2));
ang(ind) = ang(ind) + 2*pi;

% de-map
pi2 = 2*pi - pi/M;  % to ensure minimum distance decision
z = zeros(size(y));
for i = 1:size(ang,1)
    for j = 1:size(ang,2)
        minDiff = ang(i,j) - modmap;
        [tmp,ind] = min(mod(abs(minDiff), pi2));
        z(i+1,j) = ind-1;
    end
end

% --- restore the output signal to the original orientation --- %
if(wid == 1)
    z = z';
end

% Gray decode if necessary
if (strcmpi(Symbol_Ordering,'GRAY'))
    % DPSK's first element differs, In case of a rectangular
    % matrix the columns are interpreted as independent
    % column vectors (similar to frames in Simulink) with different
    % first elements
    [z_degray,gray_map] = gray2bin(z,'dpsk',M);   % Gray decode
    z = gray_map(z+1);    
end


% [EOF]