function [noise_p,w]=awgn_noise(n,snr,signal_power,channel_base_128g_201)

  %n=1;
    sn_ratio=10^((snr+3+n)/10);                               %snr為2PSK的信噪比，QPSK少3個DB，前后插零少了1.25個DB
    sigma =  sqrt (1/ ( 1 * sn_ratio) );

     
 
   % generate a uniformly distributed random number u between 0 and 1 - 1E-6*/
    u1 = rand(1,length(channel_base_128g_201))/abs(max(rand(1,length(channel_base_128g_201))));

 
 %generate a Rayleigh-distributed random number r using u */
    r =sigma*sqrt( 1* log( 1.0 ./ (1-u1 )) );
 
  u2 = rand(1,length(channel_base_128g_201))/abs(max(rand(1,length(channel_base_128g_201))));
  
 w=r .*(cos(2 * pi * u2)+j*sin(2 * pi * u2));
 noise_p=sum(abs(w).^2)/length(w);    % noise power