oqpskdemod.m

这里有一个OQPSK的源代码

function z = oqpskdemod(y,varargin)
% OQPSKDEMOD Offset quadrature phase shift keying demodulation.
%   Z = OQPSKDEMOD(Y) demodulates the complex envelope Y of an OQPSK
%   modulated signal. For two-dimensional signals, the function treats
%   each column as 1 channel. This function implicitly downsamples by a
%   factor of 2, because an odd number of samples per symbol is not allowed
%   for OQPSK.
% 
%   Z = OQPSKDEMOD(Y,INI_PHASE) specifies the phase offset (rad) of the
%   modulated signal.
%
%   See also OQPSKMOD, PSKMOD, PSKDEMOD, QAMMOD, QAMDEMOD, MODNORM.

%    Copyright 1996-2003 The MathWorks, Inc. 
%    $Revision: 1.1.6.1 $  $Date: 2003/02/14 20:50:36 $ 

% error checks
if(nargin>2)
    error('comm:oqpskdemod:numarg','Too many input arguments.');
end

%Check y, ini_phase
if( ~isnumeric(y))
    error('comm:oqpskdemod:Ynum','Y must be numeric.');
end

Nsamp = 2;

if(nargin==1 || isempty(varargin) )    
    ini_phase = 0;
else
    ini_phase = varargin{1};
    if(~isreal(ini_phase) || ~isscalar(ini_phase)|| ~isnumeric(ini_phase) )
        error('comm:oqpskdemod:ini_phaseReal','INI_PHASE must be a real scalar.');    
    end
end

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

% separate the signal into I and Q
yI = real(y);
yQ = imag(y);

%remove offset 
yQ = yQ(2:end,:);
yI = yI(1:end-1,:);

% create non-offset signal
y = yI + j*yQ;

% create the modmap
modmap = zeros(1,4);
modmap(1) = cos(ini_phase + pi/4) + j* sin(ini_phase + pi/4);
modmap(2) = cos(ini_phase + 7*pi/4) + j * sin(ini_phase + 7*pi/4);
modmap(3) = cos(ini_phase + 3*pi/4) + j * sin(ini_phase + 3*pi/4);
modmap(4) = cos(ini_phase + 5*pi/4) + j * sin(ini_phase + 5*pi/4);

%integrate.
y = intdump(y, Nsamp);

z = genqamdemod(y,modmap);

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