function  [noise]=typic_awgn(Tx_data,SNR)
% Tx_signal_power=var(Tx_data);
% noise_sigma=Tx_signal_power/SNR;
% noise_scale_factor=sqrt(noise_sigma)/sqrt(2);
%  noise=(randn(1,length(Tx_data))*noise_scale_factor;

datalength=length(Tx_data);
Tx_signal_power =var(Tx_data);
temp1=randn (1,datalength);
power_noise = mean(abs(temp1 .* conj(temp1)));
noise_sigma =Tx_signal_power/(power_noise*SNR);
ratio =sqrt(noise_sigma);
noise = temp1*ratio;

%     power_signal = mean(abs(Tx_data.* conj(Tx_data)));    
%       finger_length=length(Tx_data);%期望信號功率?????為何乘N
%        
%         temp1 = randn(1,finger_length) + j * randn(1,finger_length) ;                     %figerlenth=碼片數   randn可以負數
%         power_noise = mean(abs(temp1 .* conj(temp1)));
%         ratio = sqrt(power_signal / (power_noise * SNR));                            %?????????
%         noise=randn(1,finger_length)+j*randn(1,finger_length);                  %產生噪聲信號，根據信噪比得到
%         noise =noise.*(ratio);