function receive=channelpass(sig_in,channel,snr_db)
%信道：多徑加噪聲
avg_sig_power = sum(abs(sig_in).^2)/length(sig_in);
%求信號的平均功率
snr = power(10,snr_db/10);
%換算信噪比
avg_noise_power = avg_sig_power/(2*snr);    
% 實部或虛部的噪聲功率
real_noise = randn(length(sig_in)+length(channel)-1,1)*sqrt(avg_noise_power);
image_noise = randn(length(sig_in)+length(channel)-1,1)*sqrt(avg_noise_power);
noise_out = real_noise+j*image_noise;       
%加高斯白噪聲
% channel1=[0.26,
%           0.93,
%           0.26];                             %針對p496頁的信道情況
receive=conv(sig_in,channel)+noise_out;  
%將映射后的信號和信道做卷積，再加高斯白噪
% scatterplot(receive)                           %畫星座圖