%**************************************************************************
%Function:AWGN channel
%功能：產生AWGN信道
%function y=awgn(x,var) 
%Input: x   ---> input signal
%Input: var ---> variance
%Output: y   ---> y = x + AWGN    
%**************************************************************************
function y = awgn(x,var)
    w = randn(1,length(x));
    w = w - mean(w)*ones(size(w));
    w = sqrt(var)*(w / std(w)); 
    x = x(:); 
    w = w(:); 
    y = x + w;